NTIA TR-97-343

Assessment of Compatibility

Between 25 and 12.5 kHz Channelized

Marine VHF Radios

technical report

U.S. DEPARTMENT OF COMMERCE é National Telecommunications and Information Administration
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NTIA TR 97-343

Assessment of Compatibility

Between 25 and 12.5 kHz Channelized

Marine VHF Radios

Robert L. Sole

Frank H. Sanders

Brent Bedford

U.S. DEPARTMENT OF COMMERCE

William Daley, Secretary

Larry Irving, Assistant Secretary

for Communications and Information

August 1997
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ii

Executive Summary

The maritime mobile frequency band supports maritime communications worldwide. Appendix

18 of the ITU Radio Regulations (RR) defines the channels of the maritime mobile service. These

channels support a variety of communication functions including: public correspondence, intership

and ship-to-coast, coast- to-ship, port operations, calling and various safety purposes. Safety

functions include distress, search and rescue, ship movement, navigation (bridge-to-bridge)

communications, and maritime safety information broadcasts.

Additional maritime mobile channels are required to meet the growing demands for the above

services in the near future, particularly the demand for digital services. To accommodate the old and

new services demand for additional channels, the maritime mobile spectrum needs to be used more

efficiently. Narrowbanding of the maritime mobile VHF band from 25 kHz to 12.5 or 6.25 kHz

channel bandwidths is one possible solution to make more channels available. However, any technique

must take into account factors such as continuing to make low-cost transceivers available to the

general boating public and preserving interoperability with existing 25 kHz FM equipment. They must

also consider the time period in which these targeted improvements can be achieved. Furthermore,

any new technology used to reduce spectrum congestion and improve spectrum efficiency must be

able to accommodate existing safety and distress communications.

The United States plans to submit a proposal in the upcoming 1997 World Radio Conference

(WRC -97) to permit narrowbanding the maritime mobile VHF band. To support that proposal, the

United States Coast Guard and the National Telecommunications and Information Administration

(NTIA) conducted bench and radiated tests of 25 kHz (referred to as wideband) and 12.5 kHz

(referred to as narrowband) channelized marine radios. Commercial and recreational grade wideband

and narrowband radios were tested for susceptibility to intermodulation products and

adjacent/interstitial channel interference, and for interoperability. The narrowband radios were

prototype commercial grade radios that were not fully optimized for narrowband operation. In

addition, a VTS ship transponder receiver (as defined in ITU-R M.825) was tested for susceptibility

to adjacent channel interference.

The results of the intermodulation tests showed that commercial grade radios are less

susceptible to intermodulation products than the recreational grade radios. The results of the

adjacent/interstitial channel interference tests showed that the narrowband radios were less susceptible

to adjacent /interstitial interference than the wideband radios, both commercial and recreational grade.

The results of the VTS ship transponder tests showed that the transponder receiver performed well

in the presence of adjacent channel interference. The results of the interoperability tests showed that

the wideband radios are fully interoperable with narrowband radios, with a slight degradation in the

operating range of a wideband receiver. 
iii

Although the results of the tests showed that the wideband and narrowband radios are

interoperable, introducing narrowband radios into the existing 25 kHz environment must be carefully

done to minimize the effects of adjacent channel interference on wideband receivers. This is especially

true when the narrowband radio is operating on an interstitial channel ±12.5 kHz off-tuned from a

regular 25 kHz channel. One method that would help, but not totally eliminate, adjacent channel

interference is to ensure geographic separation between adjacently tuned narrowband radio

transmitters and wideband receivers. However, this may not be achievable in the entire maritime band

due to the fact that most of the frequency channels in the band are not exclusively assigned but shared

among a variety of users in the band. Initially, implementing separation distances to allow narrowband

operations could be done by those maritime users that have greater control over who uses their

services and who can afford narrowband capable equipment.

The range of distances that would be needed for geographic separation for adjacently tuned

wideband and narrowband radios were calculated based on data from the bench tests. The results

show that for 12.5 kHz of frequency separation from a 25 watt transmitter, the wideband radio

required about 12 nmi of separation and the narrowband radio required about 6 nmi of separation to

satisfy the test requirements. These results indicate that the narrowband radio was more immune to

adjacent channel interference than the wideband radio. The aforementioned separation distances

assume minimal degradation in receiver sensitivity for the mobile units. Operational base stations

should observe larger separation distances, especially if the working frequencies with mobile units are

simplex. Interoperability distances based on data from the bench tests showed that the wideband

receiver lost about 3 nmi of operating range when communicating with a narrowband radio, as

compared to a wideband radio. The narrowband receiver did not suffer any degradation in operating

range when communicating with the wideband transmitter, as compared to communicating with a

narrowband transmitter.
iv

Table of Contents

Section 1. Introduction

 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

 1.2 Test Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

 1.3 Test Radios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Section 2. Test Results

 2.1 Adjacent Signal Susceptibility Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

 2.1.1 Bench Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

 2.1.2 Radiated Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

 2.1.3 Adjacent Channel Separation Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

 2.1.4 Additional Radiated Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

 2.2 Interoperability Tests 

 2.2.1 Bench Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

 2.2.2 Radiated Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

 2.2.3 Co-Channel Interoperability Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

 

 2.3 Intermodulation Susceptibility Tests Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

 2.4 VTS-Like Transponder Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

 2.4.1 VTS-Like Transponder Adjacent Channel Separation Distances . . . . . . . . 2-8

Section 3. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

APPENDICES

Appendix A: Adjacent Channel Test Procedures and Recorded Data . . . . . . . . . . . . . . . . . . . A-1

Appendix B: Interoperability Test Procedures and Recorded Data . . . . . . . . . . . . . . . . . . . . . . B-1

Appendix C: Intermodulation Test Procedures and Recorded Data . . . . . . . . . . . . . . . . . . . . . C-1

Appendix D: Transponder Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-1

Appendix E: Calculating Adjacent Channel and Interoperability Distances . . . . . . . . . . . . . . . E-1

Appendix F: Test Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-1

Appendix G: Spectrum Emission Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-1
Section 1 Introduction

1-1

Section One

Introduction

1.1 Background

The maritime mobile frequency band (156-162 MHz) supports maritime communications

worldwide. Appendix 18 of the ITU Radio Regulations (RR) defines the channels of the maritime 1

mobile service. These channels support a variety of communication functions including: public

correspondence, intership and ship-to-coast, coast- to-ship, port operations, calling and various safety

purposes. Safety functions include distress, search and rescue, ship movement, navigation

(bridge-to-bridge) communications, and maritime safety information broadcasts.

 Although not used extensively, data communications are also available on some channels by

arrangement between administrations. Provisions in Appendix 18 consider the use of high-speed

data and facsimile transmissions. The Radio Regulations, primarily Articles 59 and 60 , provide

2 3

technical characteristics for these functions. Most communications in the maritime mobile service

utilize analog FM techniques for voice communications, although requirements for digital information

exchange are expected to increase in the future.

Public coast station operators have an increased need for additional spectrum with the

introduction of semi-automatic and automatic direct dial services in the U.S. Administrations where

these services have been introduced have generally seen an increase of 10-20 fold in the amount of

ship-to-shore and shore-to-ship traffic. In order to facilitate the proper implementation of automated

services, the need for additional operating channels is necessary. 

In addition, administrations implementing modern vessel traffic services (VTSs) using such

techniques as automated dependent surveillance (ADS) will need internationally compatible radio

channels set aside for data transmission. This includes the exchange of traffic and harbor data. VTS

systems will take advantage of evolving digital technology moving towards developing a "voiceless"

VTS. 

To accommodate the maritime mobile service needs for more channels, the maritime mobile

band needs to be used more efficiently. Narrowbanding of the maritime mobile VHF band from 25

kHz to 12.5 or 6.25 kHz channel bandwidths is one possible solution to making more channels

available to the services described above. However, this technique must take into account factors

such as continuing to make low-cost transceivers available to the general boating public and

preserving interoperability with existing 25 kHz FM equipment. They must also consider the time

period in which these targeted improvements can be achieved. 

Furthermore, any new technology used to reduce spectrum congestion and improve spectrum

efficiency must be able to accommodate existing safety and distress communications. Channel plans

and modulation schemes for both new and existing transceivers must be interoperable and capable

of immediately participating in the VHF maritime distress and safety system if narrowbanding is

implemented. 
Section 1 Introduction

1-2

The United States will submit a proposal in the upcoming 1997 World Radio Conference

(WRC -97) to permit narrowbanding the maritime mobile VHF band. To support that proposal, the

United States Coast Guard and the National Telecommunications and Information Administration

(NTIA) conducted bench and radiated tests of 25 and 12.5 kHz channelized marine radios. In

addition, adjacent channel interference susceptibility tests were performed on a VTS-like transponder

system. Reports documenting results of the bench and radiated tests were distributed to the maritime

industry for review and comment through the Radio Technical Commission for Maritime Services

(RTCM). This report summarizes the objectives, procedures, and results of both the radiated and

bench tests.

The VHF radio and transponder bench and radiated test objectives, procedures, and results

are discussed in the following sections. Radiated tests were performed in a maritime environment in

the South Florida area during August 1996. The bench tests were completed in April 1996 at the ITS

laboratory in Boulder, Colorado.

1.2 Test Objectives

The objectives when testing the VHF radios on a bench and in a maritime environment were

to: 1) Determine the susceptibility of 12.5 and 25 kHz channelized radios to adjacent/interstitial

channel interference, and 2) Evaluate the interoperability of the 12.5 and 25 kHz channelized radios.

The bench tests also included testing the 25 and 12.5 kHz radio’s susceptibility to intermodulation

products. The objective of the intermodulation tests was to evaluate the radios susceptibility to 3rd

and 5th order intermodulation products with pairs of frequencies located in the marine band and outof the marine band. The objective of testing the transponder was to evaluate its performance in the

presence of adjacent/interstitial channel interference.

During the radiated tests it was decided to perform additional tests beyond those described

in the original test plan circulated through RTCM. The procedures used in those tests and their results

are discussed in section 2.1.4 of this report. 

1.3 Test Radios

Production radios used for testing were commercially available analog 25 kHz channelized

marine FM radios. These 25 kHz radios included three commercial grade radios representative of the

type used by commercial boaters and government agencies. 

Most recreational boaters use less expensive low-end 25 kHz radios. These types of radios

could possibly be more susceptible to interference and interoperability problems and were therefore

also tested. NTIA purchased three fixed mount and two hand-held radios of these types from local

retailers for testing.

One manufacturer supplied two prototype 12.5 kHz channelized radios for the tests, one was

configured as a mobile and the other as a base unit. These radios are not yet commercially available.

The radios are identified by alphabetical code using letters A through K, manufacturers’ names

and model numbers are not included in this report. These radios are also identified in the bench test

report using the same letter. The radio are categorized as either recreational or commercial grade

radios and as either fixed-mount or handheld below in table 2-1.
Section 1 Introduction

1-3

The 25 kHz channelized radios will be referred to as wideband radios and the 12.5 kHz radios

will be referred to as narrowband radios for the remainder of this report. 

Table 2-1

Radio Description

Radio Type Grade

A fixed-mount recreational

25 kHz

B fixed-mount commercial

25 kHz

C fixed-mount commercial

25/12.5 kHz (prototype)

D fixed-mount commercial

25/12.5 kHz (prototype)

E hand-held recreational

25 kHz

F fixed-mount commercial

25 kHz

G hand-held recreational

25 kHz

H fixed-mount recreational

25 kHz

I fixed-mount recreational

25 kHz

J fixed-mount commercial

25/12.5 kHz (prototype)

K fixed-mount recreational

25 kHz

The tests were performed according to the radio’s mode of operation (base or mobile) and

their channel numbering plan (25 or 12.5 kHz). The proposed channel numbering plan used by the

prototype 12.5/25 kHz radios is defined in ITU Study Group 8B document 8B-TEMP/6Rev.1 (Draft

Revision of Recommendation ITU-RM.1084 , “Improved Efficiency in the Use of the Band 156-174 4

MHz by Stations in the Maritime Mobile Service”). This proposed channel numbering plan was used

in this report to denote the channels used for testing.

This recommendation was approved at the international Working Party 8B meeting held in

November 1996 and was approved by Study Group 8 in June 1997.
Section 2 Test Results

2-1

Section Two

Test Results

2.1 Adjacent Signal Susceptibility Tests

The recorded data and test procedures used in the adjacent signal susceptibility bench and

radiated tests are described in Appendix A. The following paragraphs summarize the results of the

adjacent signal susceptibility tests.

2.1.1 Bench Tests

The results of adjacent signal interference bench tests show that wideband receivers are

susceptible to narrowband interferers when the narrowband interferer is off-tuned ±12.5 kHz from

the desired signal carrier. However, wideband receivers are less susceptible to narrowband interferers

than wideband interferers when the narrowband interferers are off-tuned by at least 25 kHz from the

desired signal carrier. For example, receiver A in Table A-1 required an interference power of -59

dBm from a wideband interferer off-tuned 25 kHz to degrade the SINAD from 15 to 12 dB but, as

shown in Table A-2, -55 dBm was required for receiver A with a narrowband interferer off-tuned 25

kHz. Receiver A required 4 dB more of interference power from the narrowband interferer than the

wideband interferer to degrade the SINAD from 15 to 12 dB. Although this number varies for each

radio, it is true in all cases. Clearly, once the narrowband interferer is off-tuned 25 kHz and beyond,

the narrow band interferer is less of a concern than the wideband interferer.

These results indicate that narrowband radio transmitters would not adversely affect wideband

radio receivers operating 25 kHz and beyond from the narrowband transmitter. However,

geographical separation or sharper filtering in the wideband receiver would be necessary if the

wideband receiver was operating 12.5 kHz off-tuned from the narrowband transmitter. The cost of

additional filtering in the receiver and tighter frequency tolerances should present only a moderate

price increase to the overall cost of the radio. 

 The results of adjacent signal interference tests on narrowband receivers show they are less

susceptible to wideband interferers than wideband receivers are to narrowband transmitters. For

example, receiver A (a 25 kHz radio) in Table A-2 required an interference power of -97 dBm to

degrade the SINAD from 15 to 12 dB when the narrowband interferer was off-tuned -12.5 kHz from

the desired signal and -99 dBm for +12.5 kHz off-tuning. The desired signal power for a 15 dB

SINAD for receiver A was -114 dBm. The resulting signal-to-interference (S/I) ratios are -17 and -15

dB.

Receiver C (a 12.5 kHz radio) in Table A-7 required an interference power of -86 dBm to

degrade the SINAD from 15 to 12 dB for a wideband interferer off-tuned -12.5 kHz and -82 dBm

for 12.5 kHz off-tuning. The desired signal power for a 15 dB SINAD for receiver C was -117 dBm.

The resulting S/I ratios are -31 dB and -35 dB.

Comparing the S/I ratios of the wideband and narrowband receivers, it can be seen that the
Section 2 Test Results

2-2

narrowband radio (receiver C) has 14 dB better immunity to the wideband interferer than the

wideband radio (receiver A) has to the narrowband interferer. Although the S/I ratios are different

for each receiver, this is true for all cases of wideband receivers versus the narrowband receiver. 

 These results indicate that narrowband receivers could operate in a wideband environment

as well as wideband radios on 25 kHz channels but would require some geographical separation if

they were operating on an interstitial channel 12.5 kHz off-tuned from a regular 25 kHz channel.

The geographical separation distances for adjacently tuned wideband and/or narrowband

radios are discussed in section 2.1.3. The distances were calculated using the NTIA NLAMBDA

computer propagation model for smooth earth at 50 percent. 

2.1.2 Radiated Tests

The results of the adjacent signal interference susceptibility tests show that the narrowband

radio was more immune to adjacent channel interference than the wideband radios. The S/I ratio for

the narrowband radio was -35 dB whereas the best S/I ratio for the wideband radios (shown in Table

A-11) was -10 dB, which was determined for receiver B. Receiver G had the worst S/I of +12. These

results were expected and agreed with the results of the bench tests which also showed that the 12.5

kHz receiver with a narrower IF bandwidth is more immune to adjacent channel interference than

current wideband radios. 

 2.1.3 Adjacent Channel Separation Distances

Average channel separation distances for a wideband receiver were calculated based on the

separation distances for each wideband receiver. The distances were calculated for a wideband

receiver versus adjacently tuned wideband and narrowband transmitters off-tuned by 25 kHz, and for

a narrowband transmitter off-tuned by 12.5 kHz. The power of the adjacent transmitters was 25 watts

and three cases of antenna heights were considered: 3 meters, 3 and 10 meters, and 10 meters. The

distances were calculated based on the data in Tables A-1 and A-2 of Appendix A and the

methodology described in Appendix E. The results are shown below in Table 2-1. 

Table 2-1

Wideband Receiver Average Adjacent Channel Separation Distances (25w)

Antenna )f=25 kHz )f=12.5 kHz

Heights

25 watt 25 watt 25 watt

25 kHz Transmitter 12.5 kHz 12.5 kHz Transmitter

Transmitter

H1=3 m 1.7 nmi 1.3 nmi 11.9 nmi

H2=3 m

H1=3 m 1.9 nmi 1.7 nmi 12.6 nmi

H2=10 m

H1=10 m 1.9 nmi 1.7 nmi 13.7 nmi

H2=10m.
Section 2 Test Results

2-3

As shown in column three of Table 2-1, the separation distances for the wideband receivers

versus a narrowband transmitter, off-tuned by 25 kHz, are equivalent to the separation distances for

a wideband transmitter off-tuned by 25 kHz which are shown in column two. However, the

separation distances for the wideband receiver increase when the narrowband transmitter is tuned to

the adjacent interstitial channel. The maximum value is 13.7 nautical miles for a transmit and receive

antenna height of 10 meters. The variability in the separation distances relative to the average values

shown in Table 2-1 for the individual radios was about .4-1 nautical miles for the wideband and

narrowband interferers off-tuned by 25 kHz and about 1.7-2.6 nautical miles for the narrowband

interferer off-tuned by 12.5 kHz. 

Separation distances for a 5 watt transmitter versus a wideband receiver are shown below in

Table 2-2. 

Table 2-2

Wideband Receiver Average Adjacent Channel Separation Distances (5w)

Antenna )f=25 kHz )f=12.5 kHz

Heights

5 watt 5 watt 5 watt

25 kHz Transmitter 12.5 kHz 12.5 kHz

Transmitter Transmitter

H1=3 m 1.3 nmi 1.3 nmi 8.4 nmi

H2=3 m

H1=3 m 1.3 nmi 1.3 nmi 9.0 nmi

H2=10 m

H1=10 m 1.3 nmi 1.3 nmi 9.8 nmi

H2=10 m

Separation distances for a 1 watt transmitter versus a wideband receiver are shown below in

Table 2-3. 

Table 2-3

Wideband Receiver Average Adjacent Channel Separation Distances (1w)

Antenna )f=25 kHz )f=12.5 kHz

Heights

1 watt 1 watt 1 watt

25 kHz Transmitter 12.5 kHz 12.5 kHz

Transmitter Transmitter

H1=3 m .9 nmi .9 nmi 5.8 nmi

H2=3 m

H1=3 m. .9 nmi .9 nmi 6.3 nmi

H2=10 m.

H1=10 m .9 nmi .9 nmi 6.9 nmi

H2=10 m.
Section 2 Test Results

2-4

Table 2-1 represents the situation for a fixed mount transmitter versus a wideband receiver.

Tables 2-2 and 2-3 represent the situation for a handheld transmitter versus a wideband receiver. In

addition, Tables 2-2 and 2-3 could also represent a wideband receiver versus a fixed transmitter

limited to low power operation on certain channels. 

Adjacent channel separation distances were also calculated for a narrowband receiver versus

a wideband transmitter off-tuned by 12.5 kHz. The power of the adjacent transmitter was 25, 5, and

1 watt. Three cases of antenna heights were considered: 3 meters, 3 and 10 meters, and 10 meters.

The distances were calculated based on the data in Table A-7 of Appendix A and the methodology

described in Appendix E. The results are shown below in Table 2-4. 

Table 2-4

Narrowband Receiver Adjacent Channel Separation Distances 

Antenna )f=12.5 kHz )f=12.5 kHz )f=12.5 kHz

Heights

25 watt 5 watt 1 watt

25 kHz 25 kHz 25 kHz

Transmitter Transmitter Transmitter

H1=3 m 6.2 nmi 4.3 nmi 3.0 nmi

H2=3 m

H1=3 m 6.7 nmi 4.7 nmi 3.5 nmi

H2=10 m

H1=10 m 7.1 nmi 5.2 nmi 3.5 nmi

H2=10 m

Comparing the entries of column two in Table 2-4 and column four in Table 2-1 it can be seen

that the narrowband receiver has a smaller separation distance versus a wideband transmitter offtuned by 12.5 kHz than vice-versa. For example, the separation distance for the narrowband receiver

versus the wideband transmitter for antenna heights of 10 meters is 7.1 nautical miles. However, in

the case of the wideband receiver versus the narrowband transmitter off-tuned by 12.5 kHz (using

the same antenna heights) the separation distance is 13.7 nautical miles. Clearly the prototype

narrowband radio which uses 15 kHz wide IF filters is more immune to adjacent channel interference

than current production wideband radios that employ wide band IF’s. The narrowband radios could

be made even further immune to adjacent channel interference if the IF bandwidths were reduced to

10 kHz.

2.1.4 Additional Radiated Tests

Additional radiated tests were conducted using voice as the modulating signal for both the

interferer and desired signal transmitter. These tests were observed by attendees of the RTCM

conference. The results of these tests showed that an adjacently tuned interferer modulated by voice

could degrade performance of a voice communication link. 
Section 2 Test Results

2-5

 The results of the tests using voice-shaped noise versus voice as the modulating signal for

the interferer cannot be directly compared. The radiated test with the voice-shaped noise as the

interfering signal modulation used a 1 kHz tone to modulate the desired signal radio to conduct a

SINAD test. The SINAD test is a quantitative test that has a set goal for its results, which in our

tests was 15 dB without interference to 12 dB with interference. The radiated test with voice as the

modulating signal for the interferer and the desired signal transmitter was a qualitative test with no

direct measurement of voice or message intelligibility attempted. 

 The goal of the quantitative test was to introduce interference into the communication link

which would lower the SINAD. Lowering of the SINAD indicates that the performance of the

communication link has suffered some degradation. This was done by placing the vehicle containing

the interferer radio at a specific geographical location. With the interference being put into the link,

the 1 kHz tone could still be heard from the receiver being tested, along with noise in the background.

The background noise was due to the interferer being modulated by the VSN. When the qualitative

test was done with the interferer staying at that same location but using voice as a modulator, one

would expect to hear voice as the background interference. 

2.2 Interoperability Tests

The recorded data and test procedures used in the interoperability bench and radiated tests

are described in Appendix B. The following paragraphs summarize the results of the interoperability

tests.

2.2.1 Bench Tests

The results of the interoperability tests of a narrowband transmitter and wideband receivers

varied from radio to radio. Radio F in Table B-1 required -116 dBm of power from a narrowband

transmitter to produce a 15 dB SINAD and -116 dBm of power from a wideband transmitter.

However, radio G required -110 dBm of power from a narrowband transmitter and -115 dBm of

power from a wideband transmitter to produce a 15 dB SINAD in the receiver, a difference of 5 dB.

The other radios in Table B-1 required more power from the narrowband transmitter than the

wideband transmitter to produce the 15 dB SINAD.

In a marine environment, these differences in wideband receiver sensitivity to 25 and 12.5 kHz

transmitters would equate to some wideband radios having a reduced operating range when

communicating with narrowband radios. Some of this is due to the narrowband transmitter having

a 2 kHz signal deviation while the wideband transmitter was set to a 3 kHz signal deviation. With a

lesser signal deviation, the narrowband signal contained less energy for the wideband receiver to

demodulate.

 The results of the interoperability tests of a narrowband receiver with a wideband transmitter

in Table B-2 showed that the narrowband radio receiver required -117 dBm from a narrowband

transmitter and -119 dBm from a wideband transmitter to produce a 15 dB SINAD. Therefore,

properly designed narrowband radio receivers should be compatible with wideband transmitters with

little loss of operating range. 
Section 2 Test Results

2-6

2.2.2 Radiated Tests

The results of the interoperability tests listed in Table 5-3 showed that the wideband receivers

were compatible with the narrowband transmitter. The difference for the received desired signal

power from the narrowband and wideband transmitters at the input to the radio being tested to

achieve a 15 dB SINAD varied from 2 to 10 dB.

2.2.3 Interoperability Distances

Average interoperability distances for a wideband receiver (e.g., the distance at which a 15

dB SINAD can be attained) were calculated based on the interoperability distances for each wideband

receiver. The distances were calculated for a wideband receiver communicating with wideband and

narrowband radios transmitting at powers of 25, 5, and 1 watt for three cases of antenna heights: 3

meters, 3 and 10 meters, and 10 meters. The distances were calculated based on the desired signal

powers contained in columns two and three of Table B-1 in Appendix B and the methodology

described in Appendix E. The average interoperability distances, in nautical miles, for the wideband

receivers communicating with wideband and narrowband transmitters are shown below in Table 2-5.

Table 2-5

Wideband Receiver Average Interoperability Distances

Pt = 25 Watts Pt= 5 Watts Pt=1 Watt

Antenna 25 kHz 12.5 kHz 25 kHz 12.5 kHz 25 kHz 12.5 kHz

Heights Transmitter Transmitter Transmitter Transmitter Transmitter Transmitter

H1= 3 m 26 nmi 23 nmi 20 nmi 18 nmi 15 nmi 13 nmi

H2= 3 m

H1= 3 m 28 nmi 25 nmi 21 nmi 19 nmi 16 nmi 14 nmi

H2= 10 m

H1= 10 m 29 nmi 26 nmi 23 nmi 20 nmi 17 nmi 15 nmi

H2= 10 m

As shown in columns two through six of Table 2-5, the wideband receiver will have a minimal

loss of operating range when communicating with a narrowband transmitter, as compared to a

wideband transmitter operating at the same power output and antenna heights. On average, the

wideband receiver will only experience 2 to 3 nautical miles of degradation in operating range when

communicating with the narrowband transmitter. The variability in the interoperability distances for

the individual wideband radios relative to the averages shown in Table 2-5 was about 3.5 nautical

miles for the wideband transmitter and about 3.5 miles for the narrowband transmitter.

 Interoperability distances were also calculated for a narrowband receiver communicating with

a wideband and a narrowband radio transmitting at powers of 25, 5, and 1 watt. Three antenna

heights were considered: 3 meters, 3 and 10 meters, and 10 meters. The distances were calculated

based on the desired signal powers contained in columns two and three of Table B-2 in Appendix B

and the methodology described in Appendix E. The average interoperability distances, in nautical
Section 2 Test Results

2-7

miles, for the narrowband receiver communicating with wideband and narrowband transmitters are

shown below in Table 2-6.

Table 2-6

Narrowband Receiver Interoperability Distances

Pt = 25 Watts Pt= 5 Watts Pt=1 Watt

Antenna 25 kHz 12.5 kHz 25 kHz 12.5 kHz 25 kHz 12.5 kHz

Heights Transmitter Transmitter Transmitter Transmitter Transmitter Transmitter

H1= 3 m 29 nmi 27 nmi 23 nmi 21 nmi 17 nmi 15 nmi

H2= 3 m

H1= 3 m 30 nmi 29 nmi 24 nmi 22 nmi 18 nmi 16 nmi

H2= 10 m

H1= 10 m 32 nmi 30 nmi 25 nmi 23 nmi 19 nmi 17 nmi

H2= 10 m

As shown in columns two through six of Table 2-6, the narrowband receiver will not

experience any loss of operating range when communicating with a wideband transmitter, as

compared to a narrowband transmitter operating at the same output power and antenna heights.

These interoperability distances show that wideband receivers should be compatible with

narrowband transmitters and vice-versa, with minimal effect on the operating range of either type of

radio. 

2.3 Intermodulation Susceptibility Tests

The recorded data and the procedures used to perform the intermodulation susceptibility tests

are described in Appendix C. The following paragraphs summarize the results of the tests.

The results of the 3rd order intermodulation susceptibility tests with wideband receivers

showed a wide range of intermodulation rejection (IMR) values between manufacturers and price

range of radios. In addition, the IMR for each radio varied if the pairs of signals generating the

intermodulation products were in the receiver’s RF pass band, or out-of the receiver’s RF pass band.

For example, in Table C-1 receiver A (a recreational grade wideband radio) had an in-band IMR of

-63 dB and from Table C-2 an out-of-band IMR of -68 dB. Receiver B, a commercial grade wideband

radio, had an in-band IMR of -81 dB but saturated before a measurement could be made on the outof-band IMR.

The results of these tests indicate that front-end filtering in the radios lessen their susceptibility

to out-of-band signals that cause the intermodulation products in the radio receiver. Radio A’s out-ofband response was 5 dB better than its in-band response. The amount of additional IMR rejection for

the out-of-band signal pairs is dependent on the radio being tested.

A more important result is the difference between commercial grade and recreational grade

radios for the in-band IMR response. In this case the difference between receivers A and B is 18 dB.

In a maritime situation, this difference in IMR performance would translate into radio B having a

greater operational range than radio A, when a paging transmitter (158.700 MHz) and a rail/dock
Section 2 Test Results

2-8

transmitter (161.025 MHz) were active in the area. Although the IMR varied from radio to radio, the

commercial grade radios always had a better IMR than the recreational grade radios in these tests.

The results of the 5th order intermodulation susceptibility tests with wideband receivers

(shown in Tables C-3 and C-4) revealed that most radios, both commercial and recreational grade,

saturated before the intermodulation effects could be generated and verified. This was true for the

in-band and out-of-band signal pairs response. However, when a 5th order IMR was measured its

value was better than the 3rd order IMR response. For example, radio A’s 5th order IMR was 10

dB better than its 3rd order IMR for both the in-band and out-of-band signal pairs.

The results of the 3rd order intermodulation susceptibility tests with narrowband receivers

(radio C in Tables C-1 and C-2) showed that it had a better in-band and out-of-band IMR than the

recreational grade 25 kHz radios. As in the case of the 25 kHz radios, the out-of-band IMR was

greater then the in-band IMR. The in-band IMR was measured to be -77 dB and the out-of-band IMR

was -84 dB. These IMR’s were on par with the commercial grade wideband radios. This result was

not unexpected because the radio was a prototype of a commercial grade narrowband radio. The

manufacturer claims that production narrowband radios will come close to a -90 dB IMR. 

 Recreational grade narrowband radios were not available for this test, but should be tested

if they go into production. Currently, the FCC does not mandate IMR performance standards for

marine VHF radios sold in the United States. Many European nations require that marine radios sold

in their country adhere to the International Electrotechnical Commission (IEC) IMR specification of

-68 dB . This level was easily met by commercial grade radios in the tests but could be a problem for 5

recreational grade radios.

2.4 VTS-Like Transponder Tests

The recorded data and the procedures used to perform the transponder tests are described in

Appendix D. The following paragraphs summarize the results of the tests.

The results of the adjacent signal interference susceptibility tests on the transponder showed

that the dominant interference mechanism was front end saturation of the transponder receiver.

Receiver saturation generally occurs at high interference power levels which equates to a higher

degree of immunity to interference. 

These test results show that, with a strong desired signal, this particular VTS-like transponder

receiver was able to operate within the system with a high degree of immunity to adjacent signal

interference.

 

2.4.1 VTS-Like Transponder Adjacent Channel Separation Distances

The VTS-like transponder receiver operating on an interstitial channel would require less than

one quarter of a nautical mile of separation from a transmitter operating on the adjacent regular

marine channel (12.5 kHz of frequency separation). This assumes the VTS-like transponder receiver

has a strong desired signal (-60 dBm) and the interferer radio is transmitting with an output power

of 25 watts.
Section 3 Conclusions

3-1

Section Three

Conclusions

3. Conclusions

From reviewing the results of the bench and radiated tests, it should be possible to introduce

radios and/or VTS like systems on 12.5 kHz channels provided that proper frequency management

techniques such as geographical separation and/or receiver standards are implemented. A further

discussion of each topic is given in the following paragraphs.

Geographical separation is an option that accommodates narrowband operations for specific

licensed and/or assigned marine VHF operations, such as public coast stations and government

operations. Public coast stations are licensed by the FCC and protected to a 17 dBuV contour to

prevent interference from occurring between competitors on adjacent sites/channels. Public coast

station operators that have licenses on adjacent VHF channels in the same area could use the

interstitial between them as data or communication channels. In cases where multiple coast station

licensees operate in the same area, the interstitial channels could still be used as long as coordination

is performed between the interested parties.

Government radio communications operations in certain frequency bands are internally

coordinated and licensed, therefore implementation of 12.5 kHz channels by government users can

be conducted by using proper frequency management techniques such as geographic separations

and/or exclusive use of 12.5 kHz equipment. This situation is similar to the land mobile

implementation of interstitial 12.5 kHz channels into the existing 25 kHz environment in the 162-174

MHz and 406-420 MHz frequency bands. 

Separation distances based on bench test results show that to achieve electromagnetic

compatibility with geographic separation, wideband radios with wide IF receivers would require

about 11-13 nautical miles of separation from radios operating on adjacent narrowband channels. The

receivers of the prototype narrowband radios with narrower IF bandwidths are more resistant to

interference. These types of receivers would require about 6-7 nautical miles of geographic

separation. These distances are based on a transmit power of 25 watts and would be smaller if the

power was reduced. The receivers of the VTS-like transponders are even more resistant to

interference and would require less than a quarter mile of geographic separation to achieve

electromagnetic compatibility. 

Receiver standards are another option that could help implement narrowband operations in

the marine VHF band. Current wideband marine radios used in the tests employ IF bandwidths as

wide as the channel spacing of 25 kHz. The prototype narrowband radios used in the tests were

designed with 15 kHz wide IF’s to be compatible with both wide band and narrowband operations.

They were found to be less susceptible to adjacent channel interference than the current wideband

designs that use wide IF filters. Future 25/12.5 kHz radios could be designed with narrower IF’s for

better performance in the presence of interference without sacrificing receiver sensitivity or range.
Section 3 Conclusions

3-2

1. International Telecommunication Union (ITU) Radio Regulations. Appendix 18, Table of

Transmitting Frequencies in the Band 156-174 MHz for Stations in the Maritime Mobile Service,

1994.

2. International Telecommunication Union (ITU) Radio Regulations. Article 59, Conditions to be

Observed in the Maritime Mobile Service and in the Maritime Mobile-Satellite Service, 1994. 

3.International Telecommunication Union (ITU) Radio Regulations. Article 60, Special Rules to

the Use of Frequencies in the Maritime Mobile Service, 1994. 

4. International Telecommunication Union (ITU) Recommendation ITU-RM 1084, Improved

Efficiency in the use of the band 156-174 MHz by Stations in the Maritime Mobile Service, 1994.

5. International Electrotechnical Commission (IEC) draft IEC 1097-7, Global Maritime and

Distress and Safety System (GMDSS) Part 7: Shipborne VHF Radiotelephone Transmitter and

Receiver- Operational and Performance Requirements, Methods of Testing and Required Test

Results, 1997.

In addition, the manufacturer of the prototype narrowband radios has suggested that separate

IF filters could be used on narrowband channels. The channel space of a narrowband channel is 12.5

kHz. The IF filter does not need to be as wide as the channel spacing and could be reduced to

approximately 10 kHz. This would further reduce its susceptibility to adjacent channel interference.

Receiver intermodulation rejection standards could also be used by manufacturers as

guidelines when developing future marine VHF radios.

References
A-1

Appendix A

 Adjacent Channel Test Procedures and Recorded Data

Adjacent Channel Bench Tests

The marine VHF radios (both 25 and 12.5 kHz channelized units) were tested for susceptibility to

adjacent channel interference by using either 25 or 12.5 kHz channelized marine radios as interfering

transmitters. A diagram of the test set-up used to test the 25 kHz radios is shown below in Figure A-1. The

frequencies selected for the desired signal channel and interferer radio for the tests are described in

Appendix F.

Figure A-1

25 kHz Receiver Bench Test Set-up

The following steps were taken to perform the tests on the 25 kHz radio receivers:

1. The receiver of the 25 kHz radio under test was tuned to the desired marine channel. The test set which

was used as the 25 kHz desired signal transmitter was also tuned to that same channel and was modulated

by an internal 1 kHz tone adjusted in amplitude for a 3 kHz signal deviation. 

2. The power of the desired signal, S, from the RF output of the test set was adjusted and its value

recorded in dBm when the SINAD of the radio receiver under test was 15 dB.

3. The interferer radio was set to the proper adjacent frequency. The frequencies used by the interferer

radio and the desired signal radio for the testing are described in Appendix A.

4. The interferer radios were modulated by voice-shaped noise (VSN) played from a tape in a cassette

player. The peak amplitude of the VSN signal from the cassette tape was matched as closely as possible
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-2

to the amplitude of a 1 kHz tone that would produce a 2.5 kHz signal deviation for a 25 kHz interferer

radio. For the 12.5 kHz interferer, the peak amplitude of the VSN signal from the cassette tape was

matched as closely as possible to the amplitude of a 1 kHz tone that would produce a 1.5 kHz signal

deviation. 

5. The RF output of the interferer radio, I, was fed through the step attenuators and then through the

shielded enclosure. This signal was then combined with the desired signal, S, from the test set and

connected to the RF input of the radio being tested.

6. The interferer radio was keyed so that it would transmit. The step attenuators were set to their maximum

values and then adjusted till the interference power reduced the SINAD of the radio being tested from 15

to 12 dB.

7. The combiner at the RF input to the radio being tested was then connected to the spectrum analyzer and

the RF power of the interfering signal, I, was measured in dBm. In some instances, the power of the

interferer was below the noise floor of the spectrum analyzer. For those cases a 20 dB RF amplifier was

connected to the output of the combiner before the measurement was made.

8. The interferer radio was tuned to the next adjacent frequency from the desired channel and the above

steps were repeated till all adjacent frequencies were tested for that particular radio under test. 

For testing 12.5 kHz radio receivers, the test set was used as the interferer radio and the 12.5 kHz

radio located outside the shield room functioned as the desired signal radio. In this case, the desired signal

radio was externally modulated by a 1 kHz tone for a 2.0 kHz signal deviation and its RF power adjusted

by the step attenuators. The RF power of the test set acting as the 25 kHz interferer was adjusted from a

front panel control and externally modulated by the VSN played from the cassette player. The peak

amplitude of the VSN signal from the cassette tape was matched as closely as possible to the amplitude

of a 1 kHz tone that would produce a 2.5 kHz signal deviation from the test set acting as the interferer

radio. The test procedures were then repeated for the 12.5 kHz radio tests as in the 25 kHz radio tests,

which was to reduce the SINAD of the 12.5 kHz radio receiver from 15 to 12 dB. 

Adiagram of this test set-up is shown below in Figure A-2. The frequencies used during these tests

are described in section Appendix F.
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-3

Figure A-2

12.5 kHz Receiver Test Set-up

Adjacent Signal Bench Test Results

The results of the adjacent interference susceptibility tests are contained in the following tables.

Each table lists the desired signal power of each radio along with the power of the adjacent interferer

needed to reduce the SINAD of the radio being tested from 15 to 12 dB (for each adjacent interference

frequency).

Table A-1 contains the results of 25 kHz radio receivers versus a 25 kHz interferer on a simplex

channel.

Table A-1 

25 kHz receiver vs. 25 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-50 kHz -25 kHz 25 kHz 50 kHz

Receiver A -114 -48 -59 -58 -50

Receiver B -119 -53 -63 -61 -51

Receiver E -115 -48 -58 -59 -48

Receiver F -116 -48 -58 -59 -48

Receiver G -115 -55 -64 -62 -53

Receiver H -115 -49 -61 -58 -47

Receiver I -117 -51 -61 -60 -51

Receiver K -118 -51 -60 -60 -51
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-4

Table A-2 contains the results of 25 kHz radio receivers versus a 12.5 kHz interferer on a simplex

channel.

Table A-2 

25 kHz receiver vs. 12.5 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-50.0 -37.5 -25.0 -12.5 12.5 25.0 37.5 50.0

kHz kHz kHz kHz kHz kHz kHz kHz

Receiver A -114 -46 -51 -55 -97 -99 -54 -54 -51

Receiver B -119 -53 -55 -59 -99 -90 -59 -53 -52

Receiver E -115 -48 -51 -56 -92 -95 -56 -52 -49

Receiver F -116 -48 -50 -55 -95 -95 -55 -50 -48

Receiver G -115 -55 -58 -63 -101 -99 -60 -59 -55

Receiver H -115 -49 -55 -55 -103 -92 -54 -51 -49

Receiver I -117 -50 -53 -57 -97 -101 -56 -52 -50

Receiver K -118 -49 -52 -55 -105 -71 -54 -50 -48

Table A-3 contains the results of 25 kHz radio receivers versus a 25 kHz interferer on a duplex

channel testing the mobile receiver.

Table A-3 

25 kHz receiver vs. 25 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-50 kHz -25 kHz 25 kHz 50 kHz

Receiver A -114 -51 -60 -61 *

Receiver E -115 -48 -58 -60 *

Table A-4 contains the results of 25 kHz radio receivers versus a 12.5 kHz interferer on a duplex

channel testing the mobile receiver.

Table A-4 

25 kHz receiver vs. 12.5 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-50.0 -37.5 -25.0 -12.5 12.5 25.0 37.5 50.0

kHz kHz kHz kHz kHz kHz kHz kHz

Receiver A -114 -46 -49 -54 -129 -113 -56 -53 *

Receiver E -115 -42 -48 -52 -110 -115 -54 -50 *
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-5

Duplex communications requiresthat one radio be configured as a base unit and the other as a

mobile. Most recreational boaters do not use base station radios in regular operations on duplex channels.

For the most part base station marine radios on duplex channels in the United States are only used by those

selling public correspondence services from coast stations to commercial shipping operators. 

Table A-5 contains the results of a 25 kHz radio receiver versus a 25 kHz interferer on a duplex

channel testing the base receiver.

Table A-5 

25 kHz receiver vs. 25 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-50 kHz -25 kHz 25 kHz 50 kHz

Receiver D -119 -51 -59 -58 -51

Table A-6 contains the results of a 25 kHz radio receiver versus a 12.5 kHz interferer on a duplex

channel testing the base receiver.

Table A-6 

25 kHz receiver vs. 12.5 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-50.0 -37.5 -25.0 -12.5 12.5 25.0 37.5 50.0

kHz kHz kHz kHz kHz kHz kHz kHz

Receiver D -119 -56 -58 -61 -96 -88 -61 -56 -54

The 12.5 kHz channelized radios were tested for susceptibility to interference from a 25 kHz

interferer. The results of adjacent signal interference tests for the 12.5 kHz mobile unit on a simplex channel

versus a 25 kHz interferer are contained in Table A-7. 

Table A-7 

12.5 kHz Receiver vs. 25 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-37.5 kHz -12.5 kHz 12.5 kHz 37.5 kHz

Receiver C -117 -65 -86 -82 -64

The results of adjacent signal interference tests for the 12.5 kHz mobile unit on a duplex channel

versus a 25 kHz interferer are contained in Table A-8. 
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-6

Table A-8

12.5 kHz Receiver vs. 25 kHz Transmitter 

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-37.5 kHz -12.5 kHz 12.5 kHz 37.5 kHz

Receiver C -117 -78 -89 -82 -73

The results of adjacent signal interference tests for the 12.5 kHz base unit on a duplex channel

versus a 25 kHz interferer are contained in Table A-9.

Table A-9 

12.5 kHz Receiver vs. 25 kHz Transmitter

Radio Desired Signal Power of Adjacent Interferer (dBm)

under test Power (dBm)

-37.5 kHz -12.5 kHz 12.5 kHz 37.5 kHz

Receiver J -114 -58 -67 -65 -60

Adjacent Channel Radiated Tests

The marine VHF radios (both 25 and 12.5 kHz channelized units) were tested for susceptibility to

adjacent channel interference for the radiated tests by using either 25 or 12.5 kHz channelized marine

radios as interfering transmitters. The frequencies of the channels used in these tests are shown in Table A-2

of Appendix A.

A diagram of the test set-up used to test the 25 kHz radios is shown below in Figure A-3.

Figure A-3

25 kHz Receiver Radiated Test Set-up
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-7

The following steps were taken to perform the interference susceptibility tests on the 25 kHz radio

receivers:

1. The receiver of the 25 kHz radio (configured as a mobile) being tested on board the boat was tuned to

marine channel 87 and connected to a whip antenna. The 25 kHz desired signal transmitter (configured as

a base) was also tuned to channel 87 and modulated by an 1 kHz tone adjusted in amplitude for a 3 kHz

signal deviation. The RF output of the desired signal transmitter was connected to an antenna located on

the roof of Ross Engineering. 

2. The desired signal transmitter at the test facility was keyed. The boat moved out from the dock (located

approximately 4.5 nautical miles from the test facility) into Clearwater Harbor and stopped when the

SINAD of the radio being tested measured 15 dB with the communications test set. At that location, the

level of the desired signal power was measured (at the receiver input) in dBm with the spectrum analyzer

and its value recorded. The location of the boat was determined in latitude and longitude with a GPS

receiver.

3. The 12.5 kHz interferer radio (configured as a base) was located in a car on the boat dock

(approximately 2 miles from the boat) and was tuned to either adjacent interstitial channel 287 or 227. The

carrier of these channels are +12.5 and -12.5 kHz from the carrier of channel 87. The RF output of the

radio was connected to a 3 dB attenuator and then into adjustable RF step attenuators. The output of the

adjustable attenuators was then connected to a whip antenna mounted on the roof of the car. 

4. The interferer radio was modulated by voice-shaped noise (VSN) played from a tape in a cassette

player. The peak amplitude of the VSN signal from the cassette tape was matched as closely as possible

to the amplitude of a 1 kHz tone that would produce a 1.5 kHz signal deviation. 

5. The interferer radio was keyed so that it would transmit on either adjacent interstitial channel. The RF

power output of the interferer radio (located in the car) was adjusted with the step attenuators until the

SINAD of the 25 kHz radio being tested (located in the boat) measured 12 dB with the test set. The

location of the car was determined in latitude and longitude with a GPS receiver.

6. The cable to the RF input to the radio being tested on-board the boat was then connected to the

spectrum analyzer, and the received RF power of the interferer radio was measured in dBm with the

spectrum analyzer and its value recorded.

7. Steps one through six were repeated for each 25 kHz radio being tested.
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-8

A diagram of the test set-up used to test the 12.5 kHz radio’ssusceptibility to an adjacently tuned 25 kHz

transmitter is shown below in Figure A-4.

Figure A-4

12.5 kHz Receiver Radiated Test Set-up

The following steps were taken to perform the interference susceptibility tests on the 12.5 kHz

radio receiver:

1. The receiver of the 12.5 kHz radio (configured as a base) being tested was located at a test facility in

Tampa and was tuned to marine channel 286. The RF input to the radio was connected to adjustable RF

attenuators and then to an antenna mounted on the roof the building. The 12.5 kHz desired signal

transmitter (configured as a mobile) was also tuned to channel 286 and modulated by an 1 kHz tone

adjusted in amplitude for a 2 kHz signal deviation. The RF output of the desired signal transmitter was

connected to a whip antenna mounted on the roof of the car. 

2. The desired signal transmitter in the car was keyed up and moved to a point approximately 1 mile north

of test facility and stopped. The received desired signal power in the lab was adjusted with the attenuators

until the test set measured a 15 dB SINAD for the 12.5 kHz radio being tested. The level of the desired

signal power at the receiver input was then measured in dBm with the spectrum analyzer and its value

recorded. The location of the car containing the desired signal transmitter was determined in latitude and

longitude with a GPS receiver.

3. The 25 kHz interferer radio (configured as a mobile) was located in another car and was tuned to

channel 86. The interferer radio was modulated by voice-shaped noise (VSN) played from a tape in a

cassette player. The peak amplitude of the VSN signal from the cassette tape was matched as closely as

possible to the amplitude of a 1 kHz tone that would produce a 2.5 kHz signal deviation.
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-9

4.The RF output of the 25 kHz interferer radio was connected to a 3 dB attenuator and then into adjustable

RF attenuators. The output of the adjustable attenuators was then connected to a whip antenna mounted

on the roof of the car. 

5. The interferer radio was keyed so that it would transmit on channel 86. The car then moved south of

the test facility and stopped when the SINAD of the 12.5 kHz radio being tested measured 12 dB with the

communications test set. The location of the car containing the interferer transmitter was determined in

latitude and longitude with a GPS receiver.

6. The received power of the 25 kHz interferer radio at the input to the 12.5 kHz radio (located at the test

facility) was then measured in dBm with the spectrum analyzer and its value recorded.

7. As an additional test, the car containing the interferer radio moved closer to the test facility and stopped

when the SINAD of the radio being measured in the lab was further reduced by 2-3 dB and the 1 kHz tone

could no longer be heard. 

8. The received power of the interferer radio at the input to the 12.5 kHz radio being tested was then

measured in dBm with the spectrum analyzer and its value recorded. The GPS position of the car containing

the interferer radio was also determined.

Adjacent Channel Radiated Test Data

The results of the adjacent signal interference susceptibility tests on the 25 kHz receivers are

contained in the following paragraphs.

Column one in Table A-10 lists the radio receiver being tested. Column two lists the desired signal

power required by each 25 kHz radio to produce a 15 dB SINAD as measured with the communications

test set. Column three lists the received signal power of the adjacent narrowband transmitter at the

receiver input which reduced SINAD of the 25 kHz radio receiver from 15 to 12 dB. The narrowband

transmitter was operating on channel 227 which is -12.5 kHz off-tuned from the desired signal carrier of

channel 87. Column four lists the received signal power of the narrowband transmitter at the receiver input

which reduced the SINAD from 15 to 12 dB. In this case the interferer transmitter was operating on

channel 287, which is 12.5 kHz off-tuned from channel 87.
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-10

Table A-10

25 kHz Receiver Radiated Test Data Vs 12.5 kHz Transmitter

25 kHz Radio Desired Signal Interferer power, I (dBm)

Power,S (dBm)

-12.5 kHz off-tuned 12.5 kHz off-tuned

Channel 227 Channel 287

Receiver A -107 -100 -109

Receiver B -126 -116 -116

Receiver E -108 -94 -112

Receiver F -105 -95 -106

Receiver G -111 -112 -123

Receiver H -113 -114 -115

Receiver I -124 -114 -120

Receiver K -112 -107 -109

The signal-to-interference ratio (S/I) in dB for each radio was calculated by subtracting the

interference power, I, from the desired signal power S. The results are shown below in Table A-11. 

Table A-11

25 kHz Receiver S/I Values

25 kHz Radio Signal-to-Interference, S/I (dBm)

-12.5 kHz off-tuned 12.5 kHz off-tuned

Channel 227 Channel 287

Receiver A -7 2

Receiver B -10 -10

Receiver E -14 4

Receiver F -10 1

Receiver G 1 12

Receiver H 1 2

Receiver I -10 4

Receiver K -5 -3
Appendix A Adjacent Channel Test Procedures and Recorded Data

A-11

The location of the desired 25 kHz signal transmitter, the 12.5 kHz interferer transmitter, and the

25 kHz the radio for these tests are shown below in Table A-12.

Table A-12

25 kHz Receiver Test Locations 

Latitude Longitude

Desired Transmitter 27E 53.147' N 82E 45.679' W

Interferer Transmitter 25E 55.066' N 82E 49.950' W

Radio under test 27E 56.597' N 82E 49.520' W

The results of the adjacent signal interference susceptibility tests on the 12.5 kHz receiver are

contained in the following paragraphs.

The desired signal transmitter and the radio being tested were operating on duplex channel 286.

The desired signal transmitter was configured as a mobile and the radio being tested was configured as a

base. The 12.5 kHz receiverrequired a desired signal power, S, of -117 dBm from a 12.5 kHz transmitter

to produce a 15 dBSINAD as measured with the communications test set without interference present in

the link. 

The 25 kHz interferer was operating on duplex channel 86 and configured as a mobile. It was 12.5

kHz off-tuned from the 12.5 kHz desired signal carrier. The SINAD of the radio being tested was reduced

from 15 dB to 12 dB when the interferer power, I, at the input to the radio was -82 dBm. The resulting

signal-to-interference ratio (S/I) is -35 dB. Due to frequency licensing restrictions the 12.5 kHz radio was

not tested with a 25 kHz interferer off-tuned by -12.5 kHz. 

The locations of the desired 12.5 kHz signal transmitter, the 25 kHz interferer transmitter, and the

12.5 kHz radio for these tests are shown below in Table A-13.

Table A-13

12.5 kHz Receiver Test Locations

Latitude Longitude

Desired Transmitter 27E 54.120' N 82E 45.720' W 

Interferer Transmitter 27E 52.794' N 82E 45.701' W

Radio under test 27E 53.147' N 82E 45.679' W

In the second part of this test, the interferer moved closer to the radio under test and stopped when

the 1 kHz desired signal tone was unintelligible. At this point, the power of the interferer at the input to the

radio under test was measured to be -78 dBm. The location of the interferer was 27E 53.447' N latitude

and 82E 45.731' W longitude. 
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B-1

Appendix B

Interoperability Test Procedures and Recorded Data

Bench Tests Procedures

The interoperability of 25 and 12.5 kHz channelized marine VHF radios was bench tested by

measuring the sensitivity of 25 kHz receivers with a 12.5 transmitter and the sensitivity of 12.5 kHz

receivers with a 25 kHz transmitter. The sensitivity of 25 kHz receivers to a 12.5 kHz transmitter was

performed using the test set-up below in Figure B-1. The frequencies selected for these tests are described

in Appendix F.

Figure B-1

25 kHz Receiver Interoperability Bench Test Set-up

The following steps were taken to perform the tests on the 25 kHz radio receivers:

1. The 12.5 kHz radio was set to the same channel as the 25 kHz radio being tested.

2. The 12.5 kHz radio was modulated by a 1 kHz tone adjusted in amplitude to produce a 2 kHz signal

deviation.

3. The RF output of the 12.5 kHz radio, S, was fed through the step attenuators and then through the

shielded enclosure. This signal was then connected to the RF input of the 25 kHz radio being tested.

4. The 12.5 kHz radio was keyed so that it would transmit. The step attenuators were set to their

maximum values and then adjusted till the output power of the 12.5 kHz radio produced a 15 dB SINAD

for the 25 kHz radio being tested. 

5. The power of the desired signal, S, was measured in dBm with the spectrum analyzer and its value

recorded. 
Appendix B Interoperability Test Procedures and Recorded Data

B-2

For testing the interoperability of 12.5 kHz radio receivers with 25 kHz transmitters, the test set

was used as the desired signal transmitter. The amplitude of the internal 1 kHz tone generator in the test

set was set to a value that would produce a 3 kHz signal deviation. The RF power output of the test set

was connected to the RF input of the 12.5 kHz radio and its level adjusted through a front panel control.

The RF power of the test set was increased from -139 dBm to a value that would produce a 15 dB

SINAD on the 12.5 kHz radio. A diagram of this test set-up is shown below in Figure B-2. 

Figure B-2

12.5 kHz Receiver Interoperability Bench Test Set-up

The value of the RF power of the test set was recorded from the front panel in dBm when the SINAD

measured 15 dB. 

Bench Test Results

The results of the bench interoperability tests between a 12.5 kHz transmitter and the 25 kHz

receivers are contained in the following paragraphs.

Simplex marine channel 22A was used as the desired signal channel for testing the interoperability

of a 12.5 kHz transmitter with 25 kHz receivers. Column one in Table B-1 lists the receiver model and

column two lists the amount of power in dBm for the 12.5 kHz transmitter to produce a 15 dB SINAD in

the 25 kHz receiver. Column three lists the desired signal power in dBm from a 25 kHz transmitter required

to produce the 15 dB SINAD. 
Appendix B Interoperability Test Procedures and Recorded Data

B-3

Table B-1

25 kHz Receivers Interoperability Bench Data 

Receiver 12.5 kHz 25 kHz

Desired Signal, S Desired Signal, S

(dBm) (dBm)

Receiver A -111 -114

Receiver B -117 -119

Receiver E -114 -115

Receiver F -116 -116

Receiver G -110 -115

Receiver H -111 -115

Receiver I -113 -117

Receiver K -118 -118

The results of the bench interoperability tests between a 25 kHz transmitter and the 12.5 kHz

receivers are contained in the following paragraphs.

Simplex marine channel 22A and duplex marine channel 85 were used as the desired signal

channels for testing the interoperability of a 12.5 kHz receiver with a 25 kHz transmitter. Column one in

Table B-2 contains the receiver type or category and column two lists the amount of power in dBm

required for the 25 kHz transmitter to produce a 15 dB SINAD in the 12.5 kHz receiver. Column three

lists the desired signal power in dBm from a 12.5 kHz transmitter required to produce the 15 dB SINAD.

Radio C was used as the 12.5 kHz receiver in both cases.

Table B-2

12.5 kHz Receiver Interoperability Bench Data

Receiver 25 kHz 12.5 kHz

Desired Signal, S Desired Signal, S

(dBm) (dBm)

Simplex -119 -117

Duplex -118 -117

 

Radiated Test Procedures

The interoperability of 25 and 12.5 kHz channelized marine VHF radios was tested in a maritime

environment by measuring the sensitivity of 25 kHz receivers with a 12.5 transmitter. The sensitivity of the

25 kHz receivers with a 25 kHz transmitter was previously measured during the interference susceptibility

tests described in section 4.0 of this report. The sensitivity of 25 kHz receivers to a 12.5 kHz transmitter

was performed using the test set-up below in Figure B-3.
Appendix B Interoperability Test Procedures and Recorded Data

B-4

Figure B-3

25 kHz Receiver Interoperability Radiated Test Set-up

The following steps were taken to perform the tests on the 25 kHz radio receivers:

1. The 12.5 kHz radio and the 25 kHz radio being tested were both set to channel 87.

2. The 12.5 kHz radio was modulated by a 1 kHz tone adjusted in amplitude to produce a 2 kHz signal

deviation.

3. The RF output of the 12.5 kHz radio was connected to an antenna located on the roof of the test facility.

4. The 25 kHz receiver was located in a car. The RF input to the radio was connected to adjustable RF

attenuators and then to a whip antenna mounted on the roof of the car. The 12.5 kHz radio was keyed

so that it would transmit.

5. The car then moved 2 miles north of the test facility and stopped. The level of the received desired signal

power was then adjusted with the step attenuators till the SINAD of the radio being tested measured 15

dBwith the communications test set. At that point the power of the desired signal at the receiver input was

measured in dBm with the spectrum analyzer and its value recorded. The location of the car was

determined in latitude and longitude with a GPS receiver.

6. Steps one through five were repeated for each radio being tested.

Radiated Test Results

The results of the interoperability tests with a 12.5 kHz transmitter and the 25 kHz receivers are

contained below in Table B-3. Column one lists the 25 kHz receiver being tested, column two shows the

desired signal power at the 25 kHz receiver input required to produce a 15 dB SINAD from a 12.5 kHz

transmitter. Column three shows the desired signal power from a 25 kHz transmitter required to produce

the 15 dB SINAD. 
Appendix B Interoperability Test Procedures and Recorded Data

B-5

Table B-3

25 kHz Receivers Interoperability Radiated Data 

25 kHz Radio 12.5 kHz 25 kHz

Desired Signal, S Desired Signal, S

(dBm) (dBm)

Receiver A -115 -107

Receiver B -119 -126

Receiver E -113 -108

Receiver F -115 -105

Receiver G -116 -111

Receiver H -115 -113

Receiver I -116 -124

Receiver K -116 -112

The locations of the desired signal transmitter and the radio under test are shown below in Table

B-4.

Table B-4

Transmitter and Receiver Locations 

Latitude Longitude

Desired Transmitter 27E 53.147' N 82E 45.679' W

Radio under test 27E 54.943' N 82E 45.976' W
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C-1

Appendix C

Intermodulation Test Procedures and Recorded Data

The marine VHF radios were tested for susceptibility to 3rd and 5th order intermodulation

products by using two signal generators as interfering transmitters that could possibly generate

intermodulation products on channel 67 within the receiver of the radio being tested. A diagram of

the test set-up is shown below in Figure C-1.

Figure C-1

Intermodulation Susceptibility Test Set-up

The following steps which were taken to perform the intermodulation tests.

1. The receiver of the radio under test was tuned to marine channel 67. The test set which was used

as the desired signal transmitter was also tuned to channel 67 and was modulated by an internal 1

kHz tone adjusted in amplitude for a 3 kHz signal deviation. 

2. The power of the desired signal, S, from the RF output of the test set was adjusted and its value

recorded in dBm when the SINAD of the radio receiver under test was 15 dB.

3. The frequencies of the signal generators were set to values that could generate the 3rd or 5th order

intermodulation products on channel 67 within the radio’s receiver. Two pairs of frequencies were

chosen so that both frequencies of each pair were either in the marine band (156-174 MHz) or both

out of the marine band.

4. The RF outputs of the signal generators were FM modulated by voice-shaped noise (VSN) played

from tapes in cassette players. The peak amplitudes of the VSN signals from the cassette tapes were
C-2

matched as closely as possible to the amplitude of a 1 kHz tone that would produce a 2.5 kHz signal

deviation.

5. The RF outputs of the signal generators, I and I , were combined and fed through the shielded 1 2

enclosure. This composite signal was then combined with the desired signal, S, from the test set and

connected to the RF input of the radio.

6. The RF power of each signal generator was increased from -139 dBm in equal increments (i.e. ,

the signal generator RF output levels were kept approximately equal) until the SINAD of the radio

being tested dropped from 15 to 12 dB.

7. The SINAD reduction due to intermodulation products was verified by turning each of the signal

generators off and observing the SINAD meter on the test set. If the SINAD did not recover to 15

dB with only one signal generator present, then receiver saturation was presumed to be the dominant

interference mechanism rather than intermodulation.

7. Once the SINAD reduction due to the intermodulation product was verified, the RF power of each

signal generator, I and I , at the RF input to the radio was measured in dBm with a spectrum 1 2

analyzer and recorded. 

8. If receiver saturation occurred, then it was so noted and the tests continued. 

The CCIT audio weighting filter in the test set was not activated during these tests.

Setting Frequency Generators

Using equation C-1, two frequencies were selected to generate the 3rd order in-band

intermodulation product on channel 67. Note: F1 is tuned below F2.

In band frequencies: F1=158.700 MHz, F2=161.025 MHz

(Eq. C-1) F = 2F1 - F2 IM3

 F = 2*158.700 - 161.025 IM3 

F = 156.375 MHz, which is the carrier frequency of marine channel 67 IM3 

Equation C-2 was used to select frequencies to generate the 3rd order out-of-band

intermodulation products on channel 67.

Out-of-band frequencies: F1=151.725 MHz, F2=154.050 MHz

(Eq. C-2) F = 2F2 - F1 IM3

F = 2*154.050 - 151.725 IM3

F = 156.375 MHz, which is the carrier frequency of marine channel 67 IM3

Using equation C-3, two frequencies were selected to generate the 5th order in-band

intermodulation product on channel 67. Note: F1 is tuned below F2.
IMRSI

C-3

In band frequencies: F1=158.700 MHz, F2=159.8625 MHz

(Eq. C-3) F = 3F1 - 2F2 IM5

 F = 3*158.700 - 2*159.8625 IM5 

F = 156.375 MHz, which is the carrier frequency of marine channel 67 IM5 

Equation C-4 was used to select frequencies to generate the 5th order out-of-band

intermodulation product on channel 67.

Out-of-band frequencies: F1=152.8875 MHz, F2=154.050 MHz

(Eq. C-4) F = 3F2 - 2F1 IM5

 F = 3*154.050 - 2*152.8875 IM5 

F = 156.375 MHz, which is the carrier frequency of marine channel 67 IM5 

Calculating Intermodulation Rejection Ratio

The intermodulation rejection ratio (IMR) of the victim receiver was calculated using

equation C-5: 

(Eq. C-5)

where:

IMR= Intermodulation rejection ratio of victim receiver, in dB

S = Desired signal power for 15 dB SINAD, in dBm

I = Power of interferer, in dBm 

The IMR, S, and I for each receiver is shown below in Tables C-1 through C-4. Table C-1

contains the data for the out-of-band response and Table C-2 contains data for the in-band response

for 3rd order IMR. The powers of each interferer are almost equal, therefore the S/I was calculated

using the nominal value.
C-4

Table C-1

In-Band 3rd Order IMR Response

Radio Desired F1= 158.700 MHz

Signal, S F2= 161.025 MHz 

(dBm)

IMR (dB) I (dBm) I (dBm) 1 2

Receiver A -114 -63 -50.8 -50.5

Receiver B -119 -81 -38.7 -38.2

Receiver C -117 -77 -40.0 -39.6

Receiver D -119 -80 -40.6 -40.2

Receiver E -115 -62 -53.5 -53.2

Receiver F -116 -78 -38.7 -38.2

Receiver G -115 -61 -54.2 -53.8

Receiver G -115 -72 -43.5 -43.2

Receiver I -117 -67 -50.5 -49.8

Receiver K -118 -66 -52 -52

 Table C-2

Out-of-Band 3rd Order IMR Response

Radio Desired F1= 151.725 MHz

Signal, S F2= 154.050 MHz 

(dBm)

IMR (dB) I (dBm) I (dBm) 1 2

Receiver A -114 -68 -46.0 -46.3

Receiver B -119 saturation * *

Receiver C -117 -84 -33..5 -32.8

Receiver D -119 saturation * *

Receiver E -115 -71 -44.3 -42.3

Receiver F -116 -83 -33.2 -32.6

Receiver G -115 -71 -44.8 -44.2

Receiver H -115 saturation * *

Receiver I -117 -71 -46.6 -46.2

Receiver K -118 -69 -49 -49

Table C-3 contains the data for the out-of-band response and Table C-4 contains data for the

in-band response for 5th order IMR.
C-5

Table C-3

In-Band 5th Order IMR Response

Radio Desired F1= 158.700 MHz

Signal, S F2= 159.8625 MHz 

(dBm)

IMR (dB) I (dBm) I (dBm) 1 2

Receiver A -114 -73 -41.3 -41.0

Receiver B -119 saturation * *

Receiver D -119 -86 -33 -33

Receiver E -115 -76 -39 -39

Receiver F -116 saturation * *

Receiver G -115 saturation * *

Receiver H -115 saturation * *

Receiver I -117 saturation * *

Receiver K -118 -80 -38 -38

Table C-4

Out-of-Band 5th Order IMR Response

Radio Desired F1= 152.8875 MHz

Signal, S F2= 154.050 MHz 

(dBm)

IMR (dB) I (dBm) I (dBm) 1 2

Receiver A -114 -77 -37 -37

Receiver B -119 saturation * *

Receiver D -119 saturation * *

Receiver E -115 -81 -34 -34

Receiver F -116 saturation * *

Receiver G -115 saturation * *

Receiver H -115 saturation * *

Receiver I -117 -83 -35 -34

Receiver K -118 -82 -36 -36

The saturation values were not recorded but generally occurred at higher powers than the

intermodulation products.
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D-1

Appendix D

Transponder Test Procedures

The following steps were used to test the susceptibility of a VTS-like transponder system to a 12.5

kHz interferer tuned 12.5 kHz from the transponder channel carrier. The transponder system operates

according to the procedures outlined in ITU-R M.825 with some enhancements. The system is able to

update the status information of a participating vessel by interrogating the ship’s transponder every 10

seconds. The ship’s transponder responds to the interrogations by sending the ship’s information (i.e.,

ship’s ID, heading, speed,location, draft, cargo) back to the system controller. This information is then sent

by the controller to the other vessels participating in the system. The transponder is considered to be in

failure mode if it is not able to reply to the system controller’s interrogations for information.

The objective of this test was to inject sufficient adjacent channel interference into the transponder

receiver so that it could no longer receive the system controller’s interrogations and be put in a failure

mode.

The transponder was tested using the set-up shown below in Figure D-1.

Figure D-1

VTS-Like Transponder Test Set-up

The following steps were taken to perform the transponder tests.

1. The transponder being tested was operating as a stationary unit in the laboratory of the test facility. The

transponder was connected to a rooftop antenna and was communicating with the system controller at the

test facility via a tower located 3 miles from the building.
Appendix D Transponder Test Procedures

D-2

2. Since the transponder had already been “acquired” by the system on channel 70, it was now

communicating with the system controller on duplex channel 84 as a mobile unit. The 12.5 kHz interferer

radio was tuned to channel 284 (the interstitial 12.5 kHz offset from the carrier of channel 84) and was

modulated by VSN matched in amplitude to a 1 kHz tone that would produce a 1.5 kHz signal deviation.

The interferer was configured as a base unit operating on the interstitial channel. 

3. The RF output of the interferer radio was connected to a 3 dB attenuator and then to adjustable RF step

attenuators. The output of the attenuators was then connected to one input of a 2-to-1 RF combiner. The

other input to the combiner was connected to the cable of the rooftop antenna. The output of the combiner

was then connected to the RF input of the transponder receiver.

4. The attenuators were set to their maximum value and the interferer radio was keyed up so that it would

inject interference into the transponder.

5. The power of the adjacent channel interference was increased by decreasing the value of the step

attenuators so that the interferer would disrupt the transponder operations. The power of the interferer was

increased till the transponder could no longer respond to the system controller’s interrogations. When the

transponder was in failure mode, the power of the interferer at the input to the transponder was measured

in dBm with the spectrum analyzer and its value recorded.

Transponder Test Results

The transponder was able to respond to the controller’s polls and reach a 50% reply rate with an

interference powerof -26 dBm injected into its RF input on an adjacent interstitial channel. The transponder

was unable to receive interrogations with an interference power of -25 dBm injected into its RF input and

was considered to be in failure mode. These tests were performed while the transponder was in “distance

mode”. By switching to “local mode” the transponder could withstand an additional 2-3 dB of interference

power before failure occurred.

The desired transponder signal measured at the input to the transponder receiver was

approximately -60 dBm. The Signal-to-Interference (S/I) ratio for the 50% reply rate for the transponder

receiver was -34 dB and the S/I ratio for failure mode was -35 dB. 
E-1

Appendix E

Calculating Adjacent Channel Separation

and

Interoperability Distances

Calculating Required Path Loss and Corresponding Distance

Adjacent channel separation and interoperability distanceswere calculated for the 25 kHz and 12.5

kHz receivers byfirst determining the required path loss by using the following equations and assumptions:

(Eq. E-1) PR = PT + GT + GR - LS - LP

where:

P = Power at receiver input (defined below), dBm R

PT = Transmitter Power, dBm

G = Transmitter Antenna Gain Towards Receiver, dBi T

G = Receiver Antenna gain Towards Transmitter, dBi R

LS = System Loss, dB

LP = Required Path Loss, dB

with:

PT = 44, 37, and 30 dBm

G = 3 dBi T

G = 3 dBi R

LS = 2 dB

Rearranging equation E-1 to solve for the required path loss, L , results in equation E-2. P

(Eq. E-2) LP = PT + GT + GR - LS - PR

For the adjacent channel separation distances, the required path loss was calculated by using the

above assumptions and setting the received power, PR, equal to the received interference power values in

Tables A-1, A-2, and A-7 of Appendix A. 

For the interoperability distances, the required path loss was calculated by using the above

assumptions and setting the received power, P , equal to the received desired signal powervalues in Tables R

B-1 and B-2 of Appendix B.

Once the required path loss values were calculated, the adjacent channel separation and

interoperability distances were determined by reading the appropriate value of distance that corresponds

to the required path loss on Figures E-1, E-2, and E-3. These figures were created using the NTIA

nlambda propagation model for smooth earth at 157.1 MHz over seawater with vertical polarization at the

50 percentile. Three cases of transmit and receive antenna heights were considered: 3 m, 3 and 10 m, and

10 m. These cases were done to model communications between recreational boaters, recreational and

commercial boaters, and commercial boaters. Higher antenna heights increase the radio line-of-sight

distance and alter the path loss values.
80 

100 

120 

140 

160 

180 Path loss in dB

0 5 10 15 20 25 30 35 

Distance in Miles

Path loss

H1= 3 m H2=3 m

80 

100 

120 

140 

160 

180 

path loss in dB

0 5 10 15 20 25 30 35 

Distance in Miles

Path loss

H1=3 m H2=10 m

Appendix E Calculating Adjacent Channel and Interoperability Distances

E-2

Figure E-1

Path Loss Distance Curve, 3 m and 3 m 

Figure E-2

Path Loss Distance Curve, 3 m and 10 m
80 

100 

120 

140 

160 

180 

path loss in dB

0 10 20 30 40 

Distance in miles

Path Loss

H1=10 m H2=10 m

Appendix E Calculating Adjacent Channel and Interoperability Distances

E-3

Figure E-3

Path Loss Distance Curve, 10 m and 10 m

Sample Calculations

The following paragraphs contain sample calculations for determining the adjacent channel

separation and interoperability distances for receiver A, a 25 kHz radio. The same methodology applies

to all other 25 and 12.5 kHz radios.

Adjacent Channel Separation Distance

The received interference power for Receiver A in column four of Table A-1 is -59 dBm for a 25

kHz interferer off-tuned by -25 kHz from the desired signal. The received interference power for receiver

A from a 12.5 kHz interferer off-tuned by 12.5 kHz is -97 dBm (column 6 of Table A-2).

Setting PR in equation E-2 equal to -59 and -97 dBm and using the other assumptions, the required

path loss can be calculated for receiver A versus the 25 kHz and 12.5 kHz interferers at each level of

interferer transmitter power. The results are 107, 100 and 93 dB, and 145, 138 and 131 dB, respectively.

The corresponding distance for each required path loss can then be determined by using the

appropriate figure for the selected antenna heights. For example, for a required path loss of 107 dB the

corresponding distance for antenna heights of 3 meters can be determined from Figure E-1 to be

approximately 1.5 miles. For a required path loss of 145 dB, the corresponding distance for antenna

heights of 3 meters can be determined from Figure E-1 to be approximately 13.5 miles. Figure E-2 can be

used to determine the adjacent separation distances for antenna heights of 3 and 10 meters. Figure E-3 can

be used to determine the adjacent channel separation distances for antenna heights of 10 meters.
Appendix E Calculating Adjacent Channel and Interoperability Distances

E-4

 Adjacent channel separation distances for different scenarios/situations can be determined from the

figures by changing the assumptions for antenna gain and system loss in equation E-2.

Interoperability Distance

The desired signal power for Receiver A in column two of Table B-1 is -111 dBm for a 12.5 kHz

transmitter and in column three is -114 dBm for a 25 kHz transmitter.

Setting PR in equation E-2 equal to -111 and -114 dBm and using the other assumptions, the

required path loss can be calculated for receiver A communicating with the 12.5 kHz and 25 kHz

transmitters. The results are 159, 152 and 145 dB, and 162, 155 and 148 dB, respectively.

The corresponding distance for each required path loss can then be determined by using the

appropriate figure for the selected antenna heights. For example, for a required path loss of 159 dB, the

corresponding distance for antenna heights of 3 meters can be determined from Figure E-1 to be

approximately 25 miles. For a required path loss of 162 dB, the corresponding distance for antenna heights

of 3 meters can be determined from Figure E-1 to be approximately 28 miles. Figure E-2 can be used to

determine the interoperability distances for antenna heights of 3 and 10 meters. Figure E-3 can be used to

determine the interoperability distances for antenna heights of 10 meters. 

Interoperability distances for different scenarios/situations can be determined from the figures by

changing the assumptions for antenna gain and system loss in equation E-2.

 

Conversion To Nautical Miles

The distances chosen from the figures are in statute miles. They were converted to nautical miles

in the main report by multiplying by .87. 
F-1

 

Appendix F

Test Frequencies

Bench Test Frequencies

The following paragraphs describe the frequencies\channels used during the adjacent channel

interference susceptibility and interoperability bench tests. 

Adjacent Channel Interference Tests

The 25 kHz radios were tested for susceptibility to adjacent channel interference on simplex and

duplex channels. The 25 kHz radios were tested with both 25 and 12.5 kHz channelized radios acting as

the interferers. The 25 kHz interferers were tuned ±25 and ±50 kHz (two channels) from the desired signal

carrier frequency and the 12.5 kHz interferers were tuned ±12.5, ±25, ±37.5, and ±50 kHz from the

carrier frequency. Using this method a “baseline” measurement of the current operating 25 kHz environment

could be simulated and those results compared to the proposed 25 and 12.5 kHz environment.

The frequencies that were used by the desired signal and interferer radio during the simplex

interference susceptibility testing are shown below in Table F-1. The desired signal was transmitted on

channel 22A. On-tune interferers were not tested. The interstitial channel designations for the interferers

in Tables F-1 and F-2 are identified by adding a prefix of “2” to the previous 25 kHz channel. For example,

the interstitial channel 12.5 kHz above channel 21 is labeled 221.This channel plan designation has been

submitted to ITU-R study group 8B but has not yet been internationally adopted.

Table F-1

25 kHz Simplex Test Channels

Simplex Interferer offset value

Channel Designation Frequency kHz

(MHz)

 21A 157.0500 -50.0

 221* 157.0625 -37.5

 81A 157.0750 -25.0

 281* 157.0875 -12.5

 22 A 157.1000 0

 222* 157.1125 +12.5

 82A 157.1250 +25.0

 282* 157.1375 +37.5

 23A 157.1500 +50.0

* proposed designator

 

The frequencies that were used by the desired signal and interferer radio during the duplex

interference susceptibility testing are shown below in Table A-2. Channel 87 was the desired signal channel.
Appendix F Test Frequencies

F-2

Table F-2

25 kHz Duplex Test Frequencies

Duplex Transmit Transmit Offset value

Channel Designation Mobile Stations Base Stations (kHz) 

(MHz) (MHz)

 86 157.3250 161.9250 -50.0

 286* 157.3375 161.9375 -37.5

 27 157.3500 161.9500 -25.0

 227* 157.3625 161.9625 -12.5

 87 157.3750 161.9750 0

 287* 157.3875 161.9875 +12.5

 28 157.4000 162.0000 +25.0

 228* 157.4125 162.0125 +37.5

 88 157.4250 162.0250 +50.0

* proposed designator

When testing the 25 kHz mobile receiver on the duplex channel, the test set functioned as the

desired base station transmitter and the interferer radio located outside the shield room acted as the

adjacently tuned base station 25 or 12.5 kHz transmitter. Conversely, when testing the 25 kHz base station

receiver on the duplex channel the test set functioned as the desired mobile transmitter and the interferer

radios acted as the adjacently tuned mobile transmitter.

The radios were configured as either a base station or mobile unit. Therefore, the tests were

completed by merely selecting the proper channel for each testset-up. Internal programming in the radios

selected the proper frequency for that particular desired and interferer channel for each test. Most marine

VHF radios are sold either as a base station radio or as a mobile radio. Although, some manufacturers sell

radios that can be configured by the user as either one.

Note: In Tables F-1 and F-2 the 25 kHz interferers transmitted only on the assigned marine channels. The

12.5kHz interferers transmitted on the assigned marine channels and the interstitial channels between them.

The 12.5 kHz radios were tested for susceptibility to adjacent channel interference on simplex and

duplex channels. The 12.5 kHz radios were only tested with 25 kHz channelized radios acting as the

interferers. The 25 kHz interferer radios were off-tuned ±12.5 and ±37.5 kHz from the carrier frequency

of the desired 12.5 kHz signal. Table F-3 lists the frequencies of the simplex desired and interferer channels

tested. The interstitial channel 222A was the desired signal channel. Obviously, due to the channel plan

an on-tune 25 kHz interferer could not be tested. 
Appendix F Test Frequencies

F-3

Table F-3

12.5 kHz Simplex Test Frequencies

Simplex Interferer offset value

Channel Designation Frequency (kHz)

(MHz)

81A 157.0750 -37.5

22A 157.1000 -12.5

222A* 157.1125 0

82A 157.1250 +12.5

23A 157.1500 +37.5

* proposed designator

Table F-4 lists the frequencies of the duplex desired and interferer channels. The interstitial channel

285 was the desired signal channel.

Table F-4

12.5 kHz Duplex Test Frequencies

Duplex Transmit Transmit Offset value

Channel Designation Mobile Base Stations (kHz) 

Stations (MHz)

(MHz)

25 157.2500 161.8500 -37.5

85 157.2750 161.8750 -12.5

285* 157.2875 161.8875 0

26 157.3000 161.9000 +12.5

86 157.3250 161.9250 +37.5

* proposed designator

When testing the 12.5 kHz mobile and base receiver on the duplex and simplex channel the test

set functioned as the adjacently tuned 25 kHz interferer radio. This was accomplished by adjusting the

carrier frequency of the RF output of the test set to the values shown in Table F-4.

Interoperability Tests

Simplex channel 22A was used as the desired signal channel for testing the interoperability of a 12.5

kHz transmitter with the 25 kHz receivers. Channel 22A was also used to test the interoperability of a 25

kHz transmitter with a 12.5 kHz receiver on a simplex channel. Channel 85 was used to test the

interoperability of a 25 kHz transmitter and 12.5 kHz receiver on a duplex channel. The frequencies of

these channels are shown above in Tables F-1 and F-2.
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G-1

Appendix G

Spectrum Emission Figures

The emission spectra of the test set, a 25 kHz radio, and a 12.5 kHz radio were measured with

a spectrum analyzer and recorded with a computer. The results are shown in figures on the following pages.

The type of modulating signal and the amount of signal deviation is included in the title of each figure.
Appendix G Spectrum Emission Figures

G-2

Figure G-1

Test Set with VSN modulation and 3 kHz Deviation

Figure G-2

Test Set with 1 kHz modulation and 3 kHz Deviation, High Output
Appendix G Spectrum Emission Figures

G-3

Figure G-3

Test Set with VSN modulation and 2.5 kHz Deviation

Figure G-4

Test Set with 1 kHz modulation and 2.5 kHz Deviation, High Output
Appendix G Spectrum Emission Figures

G-4

Figure G-5

25 kHz radio with VSN modulation and 3 kHz Deviation

Figure G-6

25 kHz radio with VSN modulation and 2.5 kHz Deviation
Appendix G Spectrum Emission Figures

G-5

Figure G-7

25 kHz radio with 1kHz modulation and 3 kHz Deviation, High Output

Figure G-8

25 kHz radio with VSN modulation and 2.5 kHz Deviation, High Output
Appendix G Spectrum Emission Figures

G-6

Figure G-9

12.5 kHz radio with 1kHz modulation and 2 kHz Deviation, High Output

Figure G-10

12.5 kHz radio with VSN modulation and 1.5 kHz Deviation
Appendix G Spectrum Emission Figures

G-7

Figure G-11

12.5 kHz radio with 1kHz modulation and 1.5 kHz Deviation, High Output