**SECOND AND THIRD ADJACENT CHANNEL**

**INTERFERENCE STUDY OF FM BROADCAST RECEIVERS**

**\-\-\-\-\-\-\-\-\-\-\--**

**Project TRB-99-3**

**Interim Report**

**July 19, 1999**

Technical Research Branch

Laboratory Division

Office of Engineering and Technology

Federal Communications Commission

OET Report Prepared by:

FCC/OET TRB-99-1 William H. Inglis

July 1999 David L. Means

**Project TRB-99-3 JULY 19, 1999**

**2ND AND 3RD ADJACENT CHANNEL**

**INTERFERENCE STUDY OF FM BROADCAST RECEIVERS**

**Interim Report**

**Executive Summary**

This report presents the results of the first phase of a study intended
to produce independently developed data for the public record in Mass
Media Docket No. 99-25 and other proceedings affecting FM broadcast
service. Because of the need to develop some information quickly, this
phase of the study is limited in scope to issues of second and third
adjacent channel interference performance of analog FM receivers with
respect to analog FM interferers. Additionally the study was limited in
size to a fairly small sample of 21 receivers. Follow-on work is
anticipated to expand the study sample as well as to broaden the scope
to include digital interferer issues and investigation of the
effectiveness of additional proposed methods to mitigate interference.

Certain conclusions have been drawn concerning the study sample. First,
nearly all the receivers in the sample appear to meet or exceed the 40
dB second adjacent channel protection criterion and exceed the third
adjacent channel protection criterion by a substantial margin. Further,
there appears to be an 8-10 dB improvement in overall interference
immunity between the second and third adjacent channels across the
sample. Last, investigating the effect of reducing the maximum FM
deviation on the interfering signal indicates that a small improvement
in immunity can be expected for most receivers to second and third
adjacent channel interference.

**Background**

Currently there are two ongoing proceedings before the Commission
involving the future of the FM Broadcast radio service which raise
common technical issues requiring objectively gathered data on receiver
performance. The first of these is Mass Media Docket No. 99-25 regarding
creation of a Low Power Radio Service. A [Notice of Proposed Rule
Making]{.underline} was released February 3, 1999, requesting comment on
a variety of issues, both technical and non-technical, on a proposal to
create three new classes of licensed FM broadcast stations: a 1,000-watt
ERP primary service, and 100-watt and 1-to-10-watt ERP secondary
services. The [NPRM]{.underline} proposes that low power FM (LPFM)
stations not be subject to certain technical rules currently applied to
other classes of radio service. It states that the Commission believes
that third adjacent channel spacing restrictions are not required, and
seeks comment on whether second adjacent channel restrictions might be
disregarded as well. Comment was also requested on whether tightened
occupied bandwidth and spectral mask restrictions would be appropriate
for LPFM stations to reduce the potential for causing interference.

On October 9, 1998, USA Digital Radio Partners, L. P. (USADR) submitted
a [Petition for Rule Making]{.underline} requesting that the Commission
initiate a rule making proceeding to amend Part 73 to permit the
introduction of digital AM and FM radio broadcasting. Comments on the
[Petition]{.underline} were due December 23, 1998, and reply comments
were due January 25, 1999. USADR proposes the introduction of digital
signals on the FM band using a technique whereby a station would
transmit both its analog signal and two digital signals of lesser
amplitude \-- one on each side of the existing FM signal \-- but within
the allowed spectrum mask. Other systems are under development use
similar configurations and are commonly called \"in-band, on-channel\"
or IBOC systems. With regard to second adjacent channel interference,
USADR states that an analog second adjacent interferer will have a
negligible effect on the performance of the digital signal, and that the
interference effects of second adjacent channel IBOC signals to FM
signals should also be negligible. Regarding third adjacent channel
interference, USADR states that digital reception is essentially not
susceptible to third adjacent channel interference, nor is IBOC likely
to increase the potential for causing such interference to analog
stations.

The National Association of Broadcasters (NAB) and others have expressed
strong concerns that IBOC increases the potential for an IBOC station to
interfere with reception of the analog signal from a third adjacent
channel station due to the addition of energy around the host FM signal.
NAB concludes that third adjacent channel spacing requirements cannot be
modified and also raises concerns about second adjacent channel
IBOC-to-IBOC interference.

**Scope of the Initial Study**

Because of the need to get some objective data into the record as
quickly as possible, fairly narrow limits were imposed on the scope of
the initial study effort, both in the size of the sample of receivers
tested and in the range of tests performed. This initial study was
limited to analog interferer to analog victim cases because of the
unavailability of IBOC test signal sources and receivers. We plan, as
follow-on tasks, to both enlarge and broaden the receiver sample and to
explore the extent to which we can conduct tests more directly relevant
to IBOC digital implementation issues.

This initial study investigates the ameliorating effect on interference
of limiting the maximum deviation of the interfering signal.
Theoretically, similar effects could be achieved by limiting the maximum
modulating frequency of the interfering signal. This was not confirmed
experimentally in the initial study because of lack of equipment on hand
to properly band limit the modulation of the interfering signal. This
investigation will also be a subject of follow-on work.

**The Receiver Sample**

Considering the universe of available FM broadcast receiver types, we
have created the following four broad categories of receivers and
assigned each receiver in the sample to the appropriate category:

I. Small, inexpensive receivers with integral antenna

II\. Small, moderate-cost receivers with antenna connection

III\. Dash-mount automobile receivers

IV\. Moderately expensive audio component receivers for high quality
stereo sound systems

No Category I receivers were selected for the test sample because of the
difficulty of providing test signals at accurately controlled levels to
this type of device. It may be possible to generate meaningful data on
undesired-to desired signal ratios for Category I receivers by radiating
a composite signal for reception by the device through its integral
antenna, but such tests were prohibited by time constraints.

The test sample included five Category II receivers, seven Category III
receivers, and nine Category IV receivers, as tabulated in Table 1. All
receivers in the sample are less than twenty years old. Because of the
very small sample sizes in each category, extreme caution must be
exercised in interpretation of the data until sufficient additional
examples can be tested to improve statistical significance.

Characterization of the sample was limited to measurements of the
sensitivity of each receiver at the 50 dB quieting level. The results of
these measurements are also presented in Table 1.

# **Table 1. Receiver Sample**

+-----------------------------------------------------------------------+
| # FM Broadcast Receiver Sample Quieting Sensitivity Data              |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| ## **Make Model S/N Cat 50 dB quieting data\***                       |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| #### Panasonic SA-AK20 P7FF72002 II 18.2 uV                           |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Sharp CD-C460 70673438 II 32.1 uV                                     |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| ### Sony HCD-RX100AV 8013673 II 16.6 uV                               |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Aiwa CX-NA71U 509PM7330068 II 15.6 uV                                 |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Soundesign 5868-A 10614521 II 60.2 uV                                 |
+-----------------------------------------------------------------------+
| Model 5868-A measured 35 dB quieting                                  |
+-----------------------------------------------------------------------+
| Pioneer KEH-1060 SGTRO177570C III 1.6 uV                              |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Sony CDX-2250 3509959 III 3.4 uV                                      |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Kenwood KRC-1007 81201333 III 0.75 uV                                 |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Clarion RAX-3410 0091203 III 1.8 uV                                   |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+

Note: The test modulation for the quieting measurements was L= -R in
accordance with the procedure in IEEE Std 185-1975.

\* Except as noted

**Table 1. Receiver Sample (continued)**

+-----------------------------------------------------------------------+
| # FM Broadcast Receiver Sample Quieting Sensitivity Data              |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| ## **Make Model S/N Cat 50 dB quieting data\***                       |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Jensen CS-1000 YT55020 III 63.8 uV                                    |
+-----------------------------------------------------------------------+
| Model CS-1000 measured 38 dB quieting                                 |
+-----------------------------------------------------------------------+
| Jensen JS-6100 YT71586 III 5.6 uV                                     |
+-----------------------------------------------------------------------+
| Model JS-6100 measured 37 dB quieting                                 |
+-----------------------------------------------------------------------+
| JVC KS-FX240 104X2417 III 2.7 uV                                      |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Technics SA-EX110P-K GY8KA43249 IV 15.6 uV                            |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Sony STR-DE310 8153385 IV 20.2 uV                                     |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Onkyo TX-8211 5809070044 IV 17.6 uV                                   |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Kenwood 103AR 81000511 IV 50.6 uV                                     |
+-----------------------------------------------------------------------+
| Model 103AR measured 35 dB quieting                                   |
+-----------------------------------------------------------------------+
| Denon DRA355 60342821 IV 73.2 Uv                                      |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Aiwa AV-D55 555PM9450004 IV 53.0 Uv                                   |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| Pioneer SX-205 TCDIO21147US IV 26.3 uV                                |
+-----------------------------------------------------------------------+
| Model SX-205 measured 35 dB quieting                                  |
+-----------------------------------------------------------------------+
| Pioneer TX-950 FA3610551 IV 16.0 uV                                   |
+-----------------------------------------------------------------------+
| Model TX-950 measured 39 dB quieting                                  |
+-----------------------------------------------------------------------+
| Sherwood 59400CP 940-842825 IV 446.0 uV                               |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+

Note: The test modulation for the quieting measurements was L= -R in
accordance with the procedure in IEEE Std 185-1975.

\* Except as noted

![](media/image1.wmf){width="6.495833333333334in"
height="7.154166666666667in"}

**Test Procedure**

The interconnection of the test equipment and the equipment under test
is diagrammed in Figure 1.

The basic methodology involved operating each receiver with a desired
signal consisting of an RF carrier which was FM modulated with a 1 kHz
tone in both of the stereo channels. Two desired RF signal levels were
used: the first corresponding to the level which would be experienced by
the receiver if it were operating at the 60 dBu protected contour[^1] of
a full-power FM broadcast station. The level of distortion measured with
a desired signal level of 330 uV without impairment was used as the
baseline distortion for each receiver. The second desired signal level
is the noise limited operating point specific to the receiver under
test. This point was arrived at by reducing the desired signal level
until the unimpaired baseline distortion increased by 1%.

An undesired signal was created on first the 2nd and then the 3rd upper
adjacent channel using a stereo generator with baseband modulation
consisting of clipped pink noise. The undesired channels were modulated
with equal L and R signals without the stereo pilot because this is
often the worst-case interference condition. The undesired channels were
then modulated with stereo left channel only in order to fully exercise
the audio baseband and to maximize the amount of energy in the L - R
sidebands. The level of the undesired signal was increased until
distortion levels on the 1 kHz audio tone were measured at 1% and 3%
over unimpaired baseline levels for the 330uV desired signal level, and
the corresponding undesired signal levels were recorded. Similarly, for
the noise limited measurements, the undesired signal levels were
recorded at a 1% and 3% increases in distortion, and the
undesired-to-desired signal (U/D) ratios were computed. The tests were
repeated at peak modulation deviations of both +/- 75 kHz and +/- 50 kHz
on the undesired signal to determine the relative effect of reduced
modulation levels.

The desired signal for each test was created by FM modulating an RF
carrier at 97.5 MHz with a 1 kHz tone. In order to exercise both the
main channel and and stereo subchannel, the inputs were set at a 3dB
differential level for the left and right channels of the broadcast
stereo generator. Reducing the L input moves 10% of the power from the
main channel to the L-R stereo subchannel. Distortion was measured on
the left channel audio output of the test receiver in both cases of
undesired signal. The level of the audio signal fed to the distortion
analyzer was maintained at approximately 0 dBm to operate the audio
amplifiers in the linear portion of their output power range.

Precautions were taken to ensure against direct pickup of high-level
ambient RF signals by conducting the measurements inside a shielded
room, as well as by placing ferrites on either end of the cable
connecting the combiner to the antenna input of the receiver under test.
An isolation transformer was used on the power mains for AC-powered
receivers as well as the power supply for DC-powered receivers. An audio
linear transformer was used to isolate the audio output signal from
equipment ground.

**Observations on the Data**

The immunity data is presented in tabular form in Tables 2 through 5 for
desired signal levels at the equivalent of the protected signal contour,
and in Tables 6 through 9 for desired signal levels at the receivers\'
noise limited operating level. The same data is presented graphically in
Figures 2 through 5, and 6 through 9, respectively.

It should be noted that several of the receivers, because of their
circuit design, switched from stereo to mono reception before the 1% or
3% distortion level or the maximum undesired signal level was reached.
In these cases, the U/D value recorded in the data tables represents the
value at which the receiver switched modes. In the cases of receivers
which reached the maximum undesired signal level before the 3%
distortion level was obtained, the U/D ratio was recorded at the maximum
signal level. This tends to underestimate the receiver's ability to
reject the interfering signal for those receivers. Ten of the samples
have a maximum undesired level of 16.5 dBm which limits the maximum U/D
to 73.5 dB and twelve of the samples have a maximum undesired level of
10.5 dBm which limits the maximum U/D to 67.5 dB.

In general the receivers which reached the maximum undesired signal
level were Category III receivers for 3rd adjacent channel interference.
The effect shows up in the graphs as equal amplitude U/D ratios for
several measurements at one of the two referenced levels.

  ---------- ---------- ------------ ---------- ------------ ---------- ----------
                                                                        

                                     **Table                            
                                     2**                                

                                                                        

             2nd Adj                                                    
             U/D Ratios                                                 
             for 21                                                     
             Rcvrs at                                                   
             60 dB                                                      
             Contour                                                    

             DES Stereo                                                 
             L + R ,                                                    
             UNDES                                                      
             Stereo L                                                   
             only                                                       

                                                                        

                        75 kHz                  50 kHz                  
                        Deviation,              Deviation,              

             Sample \#  Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1          36.2         45.3       42.6         53.2       

             2          24.8         26.3       24.6         27.4       

             3          52.3         55.1       54.2         57.1       

             4          42.6         46.7       47           52.1       

             5          30.2         36.5       30.2         37.1       

             6          55.1         57.1       56           57.1       

             7          58.2         61.7       60.3         66.5       

             8          57.5         61.1       63.5         66.8       

             9          67.5         67.5       67.5         67.5       

             10         47.4         53.2       50.5         56.1       

             11         43.5         63.5       63.9         66.4       

             12         55           55.9       55.4         56.4       

             13         44.7         52.9       50.5         56.2       

             14         47.2         53.8       52.2         57.8       

             15         36.4         41.7       41.7         51.5       

             16         36.5         45.9       37.4         50.3       

             17         49.1         51.6       50           53.6       

             18         36           47.1       42.8         48.4       

             19         44.8         50.5       48           53.3       

             20         48.8         56.3       53.2         59.7       

             21         42.6         44.7       47.4         51.7       

                                                                        
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  ---------- ---------- ------------ ---------- ------------ ---------- ----------
                                                                        

                                     **Table                            
                                     3**                                

                                                                        

             2nd Adj                                                    
             U/D Ratios                                                 
             for 21                                                     
             Rcvrs at                                                   
             60 dB                                                      
             Contour                                                    

             DES Stereo                                                 
             L + R ,                                                    
             UNDES Mono                                                 
             L + R                                                      

                                                                        

                        75 kHz                  50 kHz                  
                        Deviation,              Deviation,              

             Sample \#  Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1          34.3         39.8       41.1         52.2       

             2          25.4         26.5       26.3         28         

             3          52.8         55.5       56.5         60.4       

             4          42.3         45.3       48.4         51.5       

             5          30.9         37.3       32.1         38.1       

             6          54.3         56.6       56.1         58.5       

             7          53.5         60.1       60.5         67.5       

             8          56.5         58.9       66.6         67.5       

             9          62.9         65         66.9         67.5       

             10         56.6         66.7       67.5         67.5       

             11         66.8         67.5       67.5         67.5       

             12         54.5         56.1       55.4         56.2       

             13         45.7         53         53.8         58.9       

             14         47.8         52.5       54.1         58.5       

             15         33.2         39.7       38.7         49.4       

             16         36.8         43.1       37.4         41.9       

             17         55.3         60.7       57.3         63         

             18         48.7         49.8       49           49.8       

             19         53.3         56.7       54.9         56.7       

             20         62           67.5       65.2         67.5       

             21         42.3         44.6       46.8         51         

                                                                        
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  ---------- ------------ ------------ ---------- ------------ ---------- ----------
                                                                          

                                       **Table                            
                                       4**                                

                                                                          

             3rd Adj U/D                                                  
             Protection                                                   
             Ratios for                                                   
             21 FM                                                        
             Receivers                                                    

             for 60 dBu,                                                  
             DES Stereo                                                   
             L + R, UNDES                                                 
             Stereo L                                                     
             only                                                         

                                                                          

                          75 kHz                  50 kHz                  
                          Deviation,              Deviation,              

             Sample \#    Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1            52.5         57.9       55           57.9       

             2            32.8         41.7       39.3         43         

             3            59.3         64.4       62.4         64.8       

             4            51.1         54.8       51.6         54.8       

             5            39.1         40.3       39.8         40.9       

             6            53.5         55.9       53.6         55.9       

             7            63.5         67.5       63.7         67.5       

             8            67.5         67.5       67.5         67.5       

             9            67.5         67.5       67.5         67.5       

             10           57.3         67.1       60.2         67.5       

             11           66.5         67.5       67.5         67.5       

             12           58.8         59.6       58.9         59.7       

             13           56.7         63.3       59.3         64.8       

             14           56.5         63.4       58.4         66.4       

             15           50.5         58.3       54.4         62.1       

             16           50.5         56         53.2         59.2       

             17           54.4         60         57.6         63.7       

             18           43           48.4       49.5         49.5       

             19           54.7         57.7       57.6         57.7       

             20           62.5         67.5       66.4         67.5       

             21           52.4         60.8       56.5         63.4       

                                                                          
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  ---------- ------------ ------------ ---------- ------------ ---------- ----------
                                                                          

                                       **Table                            
                                       5**                                

                                                                          

             3rd Adj U/D                                                  
             Protection                                                   
             Ratios for                                                   
             21 FM                                                        
             Receivers                                                    

             for 60 dBu,                                                  
             DES Stereo                                                   
             L + R, UNDES                                                 
             Mono L + R                                                   

                                                                          

                          75 kHz                  50 kHz                  
                          Deviation,              Deviation,              

             Sample \#    Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1            56.7         57.9       57.3         57.9       

             2            34.8         41.9       38.5         42.5       

             3            63           64.9       64.5         64.9       

             4            51.6         54.9       51.6         54.8       

             5            41.1         41.3       41.4         41.7       

             6            53.4         55.8       53.4         55.9       

             7            63.6         67.5       63.5         67.5       

             8            67.5         67.5       67.5         67.5       

             9            63           67.5       67.5         67.5       

             10           61.7         67.5       62.6         67.5       

             11           67.5         67.5       67.5         67.5       

             12           58.7         59.5       58.9         59.6       

             13           59.9         64.9       60.9         64.8       

             14           59           67.5       59.7         67.5       

             15           60.5         67.5       63.7         67.5       

             16           56.9         62.7       59.3         62.8       

             17           58.6         64.9       61.1         65.2       

             18           49.4         49.4       49.4         49.4       

             19           57.7         57.7       57.7         57.7       

             20           65.6         67.5       67.5         67.5       

             21           66.7         67.5       67.5         67.5       

                                                                          
  ---------- ------------ ------------ ---------- ------------ ---------- ----------

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                                     **Table                            
                                     6**                                

                                                                        

             2nd Adj                                                    
             U/D Ratios                                                 
             for 21                                                     
             Rcvrs at                                                   
             Noise                                                      
             Limited                                                    
             Contour                                                    

             DES Stereo                                                 
             L + R ,                                                    
             UNDES                                                      
             Stereo L                                                   
             only                                                       

                                                                        

                        75 kHz                  50 kHz                  
                        Deviation,              Deviation,              

             Sample \#  Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1          41.6         45.8       47           51.8       

             2          36.4         39.2       38.1         41.8       

             3          46.9         53.5       51.6         58.7       

             4          46.4         49.1       51.3         51.7       

             5          33           38.9       33.1         40         

             6          55.3         56.7       56           57.5       

             7          58.3         60.2       59.5         61.5       

             8          43.4         55.3       43.4         55.9       

             9          59.5         63.5       63.2         67.2       

             10         50.1         56.6       53.8         60.1       

             11         57.9         61.6       58.9         64.5       

             12         53.2         54.6       53.6         55         

             13         47.1         52.3       51.6         56.9       

             14         46.3         49.5       51.9         57.9       

             15         36.6         44.7       45           51.2       

             16         43.3         47.9       45.8         52.2       

             17         42.8         49.3       46.2         53.4       

             18         45.2         47         45.9         53.6       

             19         50.3         55.4       53.8         57.9       

             20         52.6         58.9       57.2         63.1       

             21         43.5         45.5       49.7         51.8       

                                                                        
  ---------- ---------- ------------ ---------- ------------ ---------- ----------

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  ---------- ---------- ------------ ---------- ------------ ---------- ----------
                                                                        

                                     **Table                            
                                     7**                                

                                                                        

             2nd Adj                                                    
             U/D Ratios                                                 
             for 21                                                     
             Rcvrs at                                                   
             Noise                                                      
             Limited                                                    
             Contour                                                    

             DES Stereo                                                 
             L + R ,                                                    
             UNDES Mono                                                 
             L + R                                                      

                                                                        

                        75 kHz                  50 kHz                  
                        Deviation,              Deviation,              

             Sample \#  Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1          39.2         43.5       45.8         50.4       

             2          36           38.6       37.9         41.4       

             3          47.1         52.9       55.2         61.9       

             4          45.2         46.8       51.4         51.8       

             5          33.5         38.8       33.6         40.2       

             6          54.3         56.3       56.2         57.7       

             7          55.5         59.6       59.7         62.2       

             8          44.7         55.1       50.2         57         

             9          69.3         70.9       69.6         71         

             10         62.8         68.5       64.8         70.6       

             11         67.2         69.5       67.3         71.6       

             12         53.1         54.4       53.6         54.9       

             13         46.8         50.4       54.2         58.1       

             14         44.9         46.8       53.3         56.5       

             15         36.3         41.9       42.9         48.9       

             16         39.8         48.2       45.8         52.3       

             17         49.3         57.1       51.4         57         

             18         46           47.5       45.6         52.6       

             19         57.5         59.9       58.8         59.9       

             20         66.3         66.6       66.6         66.6       

             21         43.4         45.4       48.8         51.1       

                                                                        
  ---------- ---------- ------------ ---------- ------------ ---------- ----------

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  ---------- ----------- ------------ ---------- ------------ ---------- ----------
                                                                         

                                      **Table                            
                                      8**                                

                                                                         

             3rd Adj U/D                                                 
             Ratios for                                                  
             21 FM                                                       
             Receivers                                                   
             at Noise                                                    
             Limited                                                     
             Contour                                                     

             DES Stereo                                                  
             L + R,                                                      
             UNDES                                                       
             Stereo L                                                    
             only                                                        

                                                                         

                         75 kHz                  50 kHz                  
                         Deviation,              Deviation,              

             Sample \#   Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1           54           58.3       56.1         58.3       

             2           52.5         55.3       53.5         55.6       

             3           60.7         65.2       63.6         65.3       

             4           52.6         52.9       52.6         52.8       

             5           53.1         54.5       53.8         55         

             6           53.9         55.2       53.7         55.2       

             7           63.5         66.1       63.6         66.3       

             8           54.4         57.2       54.4         57.2       

             9           69.6         71.7       71.1         72.4       

             10          62.6         69         66           72.2       

             11          64.9         69.2       68.1         72.1       

             12          58           59.3       58.1         59.4       

             13          58.9         66.5       61.2         68.4       

             14          59.2         67.1       62.3         68.2       

             15          52.8         59.3       56.6         63.3       

             16          53.6         59.6       56.9         62.9       

             17          54.1         57         57           57         

             18          51.8         63.4       52.3         66.4       

             19          55.2         57.4       57.4         57.4       

             20          65.5         68.9       68.1         68.4       

             21          54.7         61.4       58.9         64.9       

                                                                         
  ---------- ----------- ------------ ---------- ------------ ---------- ----------

![](media/image8.wmf){width="5.995833333333334in" height="4.1in"}

  ---------- ----------- ------------ ---------- ------------ ---------- ----------
                                                                         

                                      **Table                            
                                      9**                                

                                                                         

             3rd Adj U/D                                                 
             Ratios for                                                  
             21 FM                                                       
             Receivers                                                   
             at Noise                                                    
             Limited                                                     
             Contour                                                     

             DES Stereo                                                  
             L + R,                                                      
             UNDES Mono                                                  
             L + R                                                       

                                                                         

                         75 kHz                  50 kHz                  
                         Deviation,              Deviation,              

             sample \#   Dist 1%      Dist 3%    Dist 1%      Dist 3%    

             1           58.2         58.2       58.4         58.4       

             2           53.8         55.4       53.3         55.6       

             3           64.3         65         64.7         65.1       

             4           52.5         52.8       52.6         52.9       

             5           53.8         54.8       54.6         55.2       

             6           53.7         55.3       53.7         55.3       

             7           63.4         66.1       63.7         66.3       

             8           52           56.4       56.3         54.6       

             9           70.8         72.4       71           72.5       

             10          67.5         73         67.7         73.3       

             11          71.4         75.5       72.5         76.1       

             12          57.8         59.1       58           59.4       

             13          62.7         68.2       63.9         68.3       

             14          62.8         69         62.9         69         

             15          63.4         69.3       64.3         70.2       

             16          61.9         64         62.2         64.2       

             17          57           57         57           57         

             18          49.8         66.3       52           66.9       

             19          57.4         57.4       57.4         57.4       

             20          68.1         68.3       68           68         

             21          67.9         67.9       67.9         67.9       

                                                                         
  ---------- ----------- ------------ ---------- ------------ ---------- ----------

![](media/image9.wmf){width="5.9944444444444445in"
height="4.098611111111111in"}

**Conclusions**

Caution must be exercised in extending sweeping conclusions from the
data to the general population of receivers due to the small sample
size. However, some observations can conclusively be made for the sample
at hand.

Section 73.215 of the Commission's rules provides that the predicted
field strength of a potentially interfering station can be no more than
40 dB stronger than the protected field strength along a station's
protected contour. At the 3% distortion level all the receivers in the
sample, except for two (samples #2 & #6), appear to meet or exceed the
40 dB second adjacent channel protection criterion and to exceed the 40
dB third adjacent channel protection criterion by a substantial margin.
For the third adjacent channel, that margin was similar for most of the
receivers at the noise limited desired signal level and at the 60 dBu
contour.

As one would expect there are substantially greater U/D ratios for third
adjacent channel interference, because of the frequency separation and
the receiver selectivity. Overall, there appears to be approximately 10
dB better interference performance at the third adjacent channel than at
the second.

For both second and third adjacent channel interference, there appears
to be some ameliorating effect, generally on the order of several dB,
produced by reducing the maximum deviation on the undesired signal from
+/- 75 kHz to +/- 50 kHz. However, the amount of improvement varies
widely from receiver to receiver (probably due to differences in
selectivity).

**Acknowledgements**

The authors would like to acknowledge the gracious assistance provided
by the following:

Gary Hendrickson of the Measurements and Calibration Branch for
assistance with the experimental setup and the data collection; Joycelyn
Walls of the Laboratory Divison for her help with the data spreadsheets
and graphs; and Kenneth Nichols and James Higgins of the Compliance and
Information Bureau for help with the study design and procurement of
equipment.

[^1]: Equivalent to 330 uV at the antenna terminals assuming a half-wave
    dipole antenna at ten meters with a 10 dB antenna factor, including
    line losses. The antenna factor was empirically derived for the
    Roberts antenna at the FCC Laboratory.