NTIA REPORT 99-363

Evaluation of Marine VHF Radios:

Compliance to IEC Receiver Standards

Robert L. Sole

Brent Bedford

U.S. DEPARTMENT OF COMMERCE

William Daley, Secretary

Larry Irving, Assistant Secretary

for Communications and Information

October 1999
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i

Executive Summary

The maritime mobile frequencyband 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 ofcommunication 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.

Mariners in the United States and other countries are experiencing interference on channels

allocated to the above functions. The Radio Technical Commission for Maritime Services (RTCM)

established Special Committee 117 to investigate the interference and determine if the International

Electrotechnical (IEC) standard 1097-7 “Global Maritime Distress and Safety System (GMDSS)-Part

7: Shipborne VHF Radiotelephone Transmitter and Receiver-Operational and Performance

Requirements, Methods of Testing and Required Test Results” would be sufficient to protect marine

VHF radios from interference. In support of this effort, NTIA, in coordination with the Coast Guard and

RTCM SC-117, undertook a task to test nine commercial and recreational grade marine VHF radios to

the IEC standard and perform radiated test in areas where severe cases of interference are occurring.

Laboratory testing of the radios to the IEC standard was performed in Boulder, Colorado. The radiated

tests were performed in Savannah, Georgia o the Savannah River and on the Mississippi River in New

Orleans, Louisiana. Mariners in both locations have been reporting cases of severe interference in the

marine VHF band on the waterways for quite some time now. Some of the channels experiencing the

interference arekey channels used for safety and bridge-to-bridge communications. The interference is very

disruptive to normal operations on the river and is distracting to the radio operators.

The IEC laboratory tests and radiated tests were based on receiver SINAD measurements. In the

IEC 1097-7 test procedures, the SINAD of a receiver being tested was set to 20 dB by adjusting the

desired signal power and then injecting interference into the circuit to reduce the SINAD to 14 dB. The

resulting interference-to-signal radio (I/S) was then calculated in dB and compared to the minimum IEC

requirement. The IEC test procedures were used to measure the receiver sensitivity and to calculate the

receiver co-channel rejection ratio, adjacent channel selectivity, blocking (saturation) and intermodulation

rejection ratio.

All of the radios easily exceeded the minimum receiver sensitivity requirement. Four radios failed

the co-channel rejection ratio test and only two radios passed the adjacent channel selectivity test. In most

cases the radios which failed were within 3-5 dB of passing the tests. The most important IEC tests, which

are related to the complaints about interference in Savannah and New Orleans, were the intermodulation

rejection radio and blocking tests. Four radios passed the intermodulation test while only one passed the

blocking tests. Radio L, operating in local mode passed both tests and was the only radio to operate

satisfactorily in New Orleans and Savannah. Radio L had an intermodulation rejection ratio of 81 dB while

the IEC standard is 68 dB. Therefore, it can be concluded from the results of the IEC tests and radiated

tests that the IECintermodulation rejection ratio performance requirement is not stringent enough for radios

operating in some US ports and waterways.
ii

The results of these tests show that the Coast Guard and RTCM should consider the following

items when developing a marine VHF radio receiver standard based on the IEC standard: the IEC 1097-7

test procedures and performance objectives do not adequately take into account the severe intermodulation

and blocking interference that is occurring in major US ports and waterways such as Savannah and New

Orleans, the receiver standards should be based on the power levels of the unwanted signals that have been

measured in Savannah and New Orleans, and the intermodulation rejection ratio test should be referenced

from s specific wanted signal power level and a minimum SINAD, rather than a receivers maximum usable

sensitivity for a 20 dB SINAD.
iii

Table of Contents

Section 1. Introduction

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

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

1.3 Test Description .................................................... 1-2

1.4 Test Radios ........................................................ 1-2

Section 2. Test Results

2.1 Sensitivity ........................................................ 2-1

2.2 Co-Channel Rejection Ratio .......................................... 2-1

2.3 Adjacent Channel Selectivity .......................................... 2-1

2.4 Intermodulation rejection Ratio ........................................ 2-1

2.5 Blocking .......................................................... 2-2

2.6 Summary ......................................................... 2-2

Section 3. Conclusions and Recommendations ..................................... 3-1

Appendix A: Measured Data .................................................. A-1
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1-1

SECTION 1

INTRODUCTION

1.1 Background

NTIA published a report for the Coast Guard that studied the compatibility between 12.5 kHz

and 25 kHz channelized marine VHF radios, NTIA TR-97-343 “Assessment of Compatibility between

25 and 12.5 kHz Channelized Marine Radios”. One of the conclusions of the report was that the

adoption of appropriate standards for marine VHF radio receivers would help alleviate problems due to

congestion in the marine electromagnetic environment. Currently, the United States does not have receiver

standards for marine VHF radios. An organization comprised of mariners, radio manufacturers, and

frequency regulators, the Radio Technical Commission for Maritime services (RTCM), established RTCM

SC-117 to investigate receiver standards developed by other regulatory agencies or organizations. One

organization, the International Electrotechnical Commission (IEC), has recently published a document that

contains proposed standards for marine VHF radios. 

The IEC’s standards for marine radios are in a document titled “IEC 1097-7: Global Maritime

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

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

Results”.

The Coast Guard is interested in establishing voluntary standards, similar to the IEC standard, for

marine VHF radios sold in the United States to help protect them from interference. In support of this

effort,NTIA, in coordination with the Coast Guard and RTCM SC-117, undertook a task to test nine

commercial and recreational grade marine VHF radios to the IEC standard and perform radiated tests in

areas where severe cases of interference are occurring. Laboratory testing of the radios to the IEC

standard was performed in Boulder, Colorado. The radiated tests were performed in Savannah, Georgia

onthe Savannah River and on the Mississippi River in New Orleans, Louisiana. These locations were

chosen for “live” testing due to the numerous complaints from mariners that their communications are being

disrupted on the Savannah and Mississippi Rivers due to interference in the marine VHF band.

The IEC laboratory procedures and standards are based on receiver SINAD measurements and

Interference-to-signal (I/S) ratios. A receiver SINAD measurement is the ratio, expressed in dB, of the

desired signal power to interference, noise, and distortion. An I/S ratio, expressed in dB, is the level of the

unwanted signal to the wanted signal. In the IEC test procedures, the SINAD of a receiver being tested

was set to 20 dB by adjusting the desired signal power and then injecting interference into the circuit to

reduce the SINAD to 14 dB. The resulting interference-to-signal ratio (I/S) was then calculated in dB and

compared to the minimum IEC requirement. The radio either passed or failed the test. The IEC test

procedures were used to measure the receiver sensitivity and to calculate the receiver co-channel rejection

ratio, adjacent channel selectivity, blocking (saturation) and intermodulation rejection ratio. 
1-2

1.2 Test Objectives

The objective of these tests was to determine the marine VHF radios compliance to the

performance standards for marine VHF radio receivers contained in IEC document 1097-7. The specific

laboratory tests that were performed from IEC document 1097-7 are shown in Table 1-1. 

Table 1-1

IEC

Test

Section 5.5.3

Sensitivity

Section 5.5.4

Co-Channel Rejection Ratio

Section 5.5.5

Adjacent Channel Selectivity

Section 5.5.7

Intermodulation Response

Section 5.5.8

Blocking

1.3 Test Description

The radios were tested by using signal generators to provide the wanted and unwanted signals. The

signals were combined with a RF network and then injected into the RF input of the radios. A

communication test set was used for receiver SINAD measurements.

The first task of the tests was to determine the power required at the radio’s RF input that would

produce a 20 dB SINAD in the radio receiver. Each interference test used that as a starting point and then

unwantedsignal(s) were injected into the radio receiver to lower the SINAD to 14 dB. The power of the

unwantedand wanted signals were then used to calculate an interference-to-signal (I/S) ratio in dB which

was then compared to the IEC minimum test requirement. If the radio met or exceeded the requirement

of the test that was being performed then it passed, otherwise it failed.

1.4 Test Radios

Commerciallyavailable analog 25 kHz channelized marine VHF FM radios were tested. These 25

kHz radios included four commercial grade radios representative of the type used by commercial boaters

and government agencies.

Most recreational boaters use less expensive 25 kHz radios that retail for under 300 dollars. These

types of radios, which were found to be more susceptible to interference, were also tested. NTIA

purchased three fixed mount and two hand-held radios of these types from local retailers for testing.

The radios are identified by alphabetical code. Manufacturers’ names and model numbers are not

included in this report. The radios are categorized as either recreational or commercial grade radios and

as either fixed-mount or handheld below in Table 1-2.
1-3

Table 1-2

Radio Description

Radio Type Grade

A fixed-mount

25 kHz

recreational

B fixed-mount

25 kHz

commercial

E hand-held

25 kHz

recreational

F fixed-mount

25 kHz

commercial

G hand-held

25 kHz

recreational

H fixed-mount

25 kHz

recreational

I fixed-mount

25 kHz

recreational

K fixed-mount

25 kHz

recreational

L fixed-mount

25 kHz

commercial

Radio L had a local/distance switch for its receiver accessible on a front panel control which was

separate from the squelch control. The local/distance switch is used by the radio operator to reduce the

sensitivity of the radio receiver by about 10 dB to compensate for strong undesired signals in the

electromagnetic environment. This radio was designed with these features for operations in congested EM

environments. 
2-1

SECTION 2

TEST RESULTS

2.1 Receiver Sensitivity

The IEC minimum requirement for this standard is 1FV at the radio RF input for a 20 dB SINAD.

This level is equal to -107 dBm into a 50 ohm load. The sensitivity of the radios was measured at channels

01A (156.050 MHz), 16 (156.800 MHz), 67 (156.375 MHz), 70 (156.525 MHz), and 87 (161.975

MHz). All of the radios met or exceeded the 1FV requirement, including radio L operating in the local and

distance modes. Table A-2 in Appendix A contains the measured data for the radio sensitivity tests.

2.2 Co-Channel Rejection Ratio

The IEC requirement for this standard is -10 to 0 dB, calculated as the ratio of the unwanted

signal to wanted signal which would degrade the SINAD from 20 to 14 dB. Channel 67 was used as the

wantedsignal for this test. Radio G, H, I, K, and L met the requirement of this standard. Radios A, B, E,

and F failed. Radios A and B failed by 1 dB while radio E failed by 2 dB and radio F failed by 4 dB. Table

A-4 in Appendix A contains the measured data for the co-channel rejection ratio tests.

2.3 Adjacent Channel Selectivity

The IEC minimum requirement for this standard is 70 dB, calculated as the ratio of the unwanted

signal to wanted signal which would degrade the SINAD from 20 to 14 dB. Channel 67 (156.375 MHz)

was used as the wanted signal channel for this test and the unwanted signals were set at channel 8 (156.400

MHz) and channel 07A (156.350 MHz). Commercial grade Radios B and F passed this test. The only

recreational grade radio to pass this test was radio K. Table A-3 in Appendix A contains the measured

data for the radios adjacent channel selectivity test. 

2.4 Intermodulation Rejection Ratio

The IEC minimum requirement for this standard is 68 dB, calculated as the ratio of unwanted signal

to wanted signal which would degrade the SINAD from 20 to 14 dB. The unwanted signals are set to

frequencies 50 kHz and 100 kHz removed from the wanted signal channel to generate a third order

intermodulation product within the radio receiver on the wanted signal channel. Channel 67 was the wanted

signal channel for this test and the unwanted signals were set at channels 68 (156.425 MHz) and channel

69 (156.475 MHz). The power of the unwanted signals at the radio RF input were set to equal levels. 

Radios B, F, H, and L passed this test. Radio L was the best performer and passed the test by

18 dB with the receiver operating in distance mode and by 16 dB operating in local mode.

Table A-5 in Appendix A contains the measured data for the radio intermodulation tests. The results of this

test are important because this is the type of interference that is occurring at New Orleans and Savannah.

The frequency separation between the wanted signal and the unwanted signals (50 and 100 kHz)

was seen to generate interference effects other than intermodulation products within the radio receiver. This

topic is discussed below.

Further investigation of this test revealed that in some instances the reduction in the SINAD was
2-2

not totally due to an intermodulation product, but also included adjacent channel interference effects as well.

This was verified by turning off the RF output of each of the unwanted signal generators one at a time. With

only one unwanted signal connected into the test circuit the intermodulation product could not be generated

and the SINAD should have recovered to approximately 20 dB. In some cases when the unwanted signal

on channel 68 was transmitting into the circuit and the unwanted signal on channel 69 was not, the SINAD

did not recover to 20 dB. When the situation was reversed the SINAD generally recovered to a higher

value. This result indicated that adjacent channel interference was also contributing to the SINAD reduction

and that the effect was more pronounced with the closest unwanted signal (channel 68) operating in the

circuit. The level of this effect varied with each radio.

Additional tests on radio L showed that as the frequency separation between the wanted signal and

unwanted signals increased, the SINAD recovered to a higher value indicating that the adjacent channel

effects were becoming less of a factor. The “break point” is the amount of frequency separation between

the wanted signal channel and the unwanted signals where the reduction in the SINAD is a result of the

intermodulation product and not adjacent channel interference.

2.5 Blocking 

The IEC requirement for this standard is 90 dBFV (emf), which would degrade the SINAD to 14

dB. This level equates to a power of -23 dBm at the RF input of the test radio. Channel 67 was used as

the desired signal channel for this test. The unwanted signal was set at frequencies of "10, "5, "2, and

"1 MHz from channel 67 for this test. 

The only radio that was able to pass this test for the entire frequency range was radio L operating

in local mode. The other radios were able to pass the test at the far frequencies but failed as the unwanted

signal was within "2 MHz and"1 MHz of the wanted signal. Radio L had the best overall performance

while operating in local mode. This radio was able to take up to -14 dBm of unwanted signal power, which

is 9 dB above the IEC requirement, and still meet the IEC sensitivity requirement. Tables A-6 and A-7 in

Appendix A contain the measured data for the radio blocking tests.

2.6 Summary

The commercial grade radios performed better than the recreational grade radios by passing more

of the test requirements. None of the radios were able to pass all of the tests. The best performer was

Radio L. Operating in local mode it passed all of the tests except for the adjacent channel selectivity test.

The results show that the blocking test requirement was the hardest test for the radios to pass. This test is

very important because blocking type interference is occurring in US ports and waterways and the

measured levels of the unwanted signals exceed the IEC requirement by 8 dB. 
3-1

SECTION 3

CONCLUSIONS and RECOMMENDATIONS

The following conclusions and recommendations can be drawn from the results of IEC 1097-7

tests performed on the radios in the laboratory. The performance requirements of the IEC tests were

evaluated by the radiated testing which was performed on the Mississippi River in New Orleans, Louisiana

and the Savannah River in Savannah Georgia. The results of the radiated tests are discussed in NTIA

Report 99-362.

3. Conclusions

1.The marine radios that were tested, which are typical of the types sold to recreational boaters and

commercial mariners, easily met or exceeded the IEC minimum receiver sensitivity requirement of 1FV (for

a 20 dB SINAD). 

2. Except for radio L operating in local mode, radios that passed the IEC intermodulation rejection ratio

test of 68 dB were still susceptible to intermodulation interference at Savannah and New Orleans.

Therefore, the performance requirement of the intermodulation rejection ratio test set by IEC is not stringent

enough for marine radios operating in/near major US ports and waterways.

3.In some radios, the 50 kHz and 100 kHz spacing between the wanted and unwanted signals for the

intermodulation rejection ratio test resulted in adjacent channel interference occurring along with the

intermodulation interference. The adjacent channel interference further reduced the SINAD measurement

and affected the results of the intermodulation rejection ratio test. 

4.Referencing the unwanted signal power levels in the IEC intermodulation rejection ratio test to the

maximum usable receiver sensitivity results in the unwanted signal power levels being lower than those

measured in New Orleans and Savannah because the receivers have sensitivities that far exceed the IEC

requirement of 1FV. 

3.1 Recommendations

It is recommended that the Coast Guard and RTCM consider the following items when developing

a VHF marine radio receiver standard.

1. The IEC 1097-7 test procedures and performance objectives do not adequately take into account the

severe intermodulation and blocking interference that is occurring in major US ports and waterways, such

as Savannah and New Orleans.

 

2.A VHF marine radio receiver standard developed by the Coast Guard and RTCM should be based on
3-2

the power levels of the unwanted signals that have been measured in Savannah and New Orleans.

3. A VHF marine radio receiver standard developed by the Coast Guard and RTCM should reference the

intermodulation rejection ratio test from a specific wanted signal power level and a minimum SINAD, rather

than the IEC procedure which is based on a receivers maximum usable sensitivity for a 20 dB SINAD .
A-1

Appendix A

Measured Data

This appendix contains the measured data that was recorded for each radios laboratory

tests and the I/S ratios that were calculated using that data. A summary pass/fail table is shown

below in Table A-1. The recorded data on each test is presented in the following tables: Table

A-2 Sensitivity tests, Table A-3 Adjacent Channel Interference tests, Table A-4 Co-Channel

interference Tests, Table A-5 Intermodulation Interference Tests, and Tables A-6 and A-7

Blocking Tests. Radio L has data entries for local and distance mode operation. The power of

the unwanted signals is measured at the RF input of the test radios for all tests.

Table A-1

Radio IEC Test

5.5.3

Sensitivit

y

5.5.4

Co-Channel

Rejection

5.5.5

Adjacent Channel

Selectivity

5.5.7

Intermodulation

Response

5.5.8

Blocking

A pass fail fail pass fail

B pass fail pass pass fail

E pass fail fail fail fail

F pass fail pass pass fail

G pass pass fail fail fail

H pass pass fail pass fail

I pass pass fail pass fail

K pass pass pass fail fail

L Distance

 Local

pass

pass

pass

pass

fail

fail

pass

pass

fail

pass
A-2

IEC 5.5.3 Sensitivity

The IEC sensitivity requirement is 1FV at the RF input of the radio that would produce a 20 dB SINAD. This equates

to a power level of -107 dBm at the RF input of the test radio. 

Table A-2

Sensitivity Test Measured Data

radio Sensitivity (dBm) pass/fail

A -113 pass

B -120 pass

E -115 pass

F -116 pass

G -116 pass

H -114 pass

I -116 pass

K -116 pass

L Distance

 Local

-117

-107

pass

pass

IEC 5.5.5 Adjacent Channel Selectivity

The IEC requirement for adjacent channel selectivity is 70 dB, calculated as the level of the unwanted signal to the level

of the wanted signal which degrades the receiver SINAD from 20 to 14 dB.

Table A-3

Adjacent channel Interference Test Measured Data

radio Sensitivity 

(dBm)

-25 kHz Off-tuned

interferer (dBm)

I/S

(dB)

+25 kHz Off-tuned

Interferer (dBm)

I/S

(dB)

pass/fail

A -113 -45 68 -44 69 fail

B -120 -47 73 -44 76 pass

E -115 -48 67 -49 66 fail

F -116 -38 78 -39 77 pass

G -116 -58 58 -57 59 fail

H -114 -47 67 -44 70 fail

I -116 -47 69 -46 70 fail

K -116 -45 71 -44 72 pass

L Distance

 Local

-117

-107

-68

-59

49

48

-67

-58

50

49

fail

fail

 
A-3

IEC 5.5.4 Co-Channel Rejection Ratio 

The IEC requirement for the Co-Channel rejection ratio -10 to 0 dB, calculated as the level of the

unwanted signal to the level of the wanted signal which degrades the receiver SINAD from 20 to 14 dB. 

Table A-4

Co-Channel Test Measured Data

radio Sensitivity

(dBm)

Interferer 

(dBm)

I/S

(dB)

pass/fail

A -113 -124 -11 fail

B -120 -131 -11 fail

E -115 -127 -12 fail

F -116 -130 -14 fail

G -116 -125 -9 pass

H -114 -122 -8 pass

I -116 -124 -8 pass

K -116 -125 -9 pass

L Distance

 Local

-117

-107

-124

-115

-7

-8

pass

pass

IEC 5.5.7 Intermodulation Rejection Ratio 

The IEC requirement for intermodulation rejection ratio is 68 dB, calculated as the ratio of the unwanted signal to the level

of the wanted signal which degrades the receiver SINAD from 20 to 14 dB. 

Table A-5

Intermodulation Test Measured Data

radio S, (dBm) I1 and I2 (dBm) I/S ratio (dB) pass/fail

A -113 -46 67 fail

B -120 -48 72 pass

E -115 -52 63 fail

F -116 -39 77 pass

G -116 -55 61 fail

H -114 -42 72 pass

I -116 -50 66 fail

K -116 -54 62 fail

L Distance

 Local

-117

-107

-34

-26

83

81

pass

pass

IEC 5.5.8 Blocking Test
A-4

The IEC requirement for blocking is 90 dBFV (emf), with the unwanted signal at -10 to -1 MHz off-tuned and -1 to 10

MHz off-tuned from the wanted signal that would degrade the SINAD from 20 to 14 dB. This equates to a signal level of -23 dBm

at the RF input of the test radio. 

Table A-6

Blocking Test Measured Data

radio I (dBm) pass/fail

-10 MHz -5 MHz -2 MHz -1 MHz

A -14 -14 -23 -23 pass

B -19 -20 -29 -29 fail

E -16 -16 -24 -25 fail

F -24 -19 -22 -22 fail

G -18 -19 -26 -28 fail

H -14 -14 -29 -23 fail

I -16 -20 -24 -24 fail

K -16 -17 -26 -26 fail

L Distance

 Local

-19

-5

-19

-5

-24

-14

-23

-14

fail

pass

Table A-7

Blocking Test Measured Data

radio I (dBm) pass/fail

+10 MHz +5 MHz +2 MHz +1 MHz

A -19 -21 -24 -24 fail

B -19 -19 -25 -28 fail

E -17 -24 -24 -25 fail

F -15 -15 -22 -22 pass

G -19 -27 -28 -28 fail

H -14 -14 -21 -19 pass

I -18 -20 -24 -24 fail

K -16 -19 -24 -24 fail

L Distance

 Local

-16

-4

-17

-4

-24

-12

-24

-14

fail

pass