[SBE] Aircraft radios.. cross posted

[Deese, David]

We had a similar situation in Nashville a few years ago with a complaint by
pilots that 560 AM was interfering.  The FAA sent out an engineeri who
monitored the station for hours looking for a spur and found none.  The
conclusion the FCC came to was that someone was using a low powered FM
transmitter to rebroadcast the station beyond 560's normal coverage area.
That transmitter was using an aircraft frequency.  Being low power the
interference was sporadic since the area where pilots had the interference
was very rural.  I never heard if they actually found the offender, but the
problem seemed to go away.

 

David Deese  CBT

Trevecca Nazarene University

 

From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org] On Behalf Of Edwin
Bukont
Sent: Wednesday, September 26, 2012 6:56 AM
To: radio-tech at broadcast.net; pub tech; sbe
Subject: [SBE] Aircraft radios.. cross posted

 

For those familiar with commercial aviation... question.
 
Am curious if those who follow commercial aviation, especially the radios
used in commercial planes, are aware of any recent significant changes to
radios, perhaps something added.  Or a new make/model of some receiver that
might be recently deployed.
 
Have a strange interference complaint which makes no sense.  I have been all
over the client's transmitters with scanner and spectrum analyzer.  Driven
the major airports and a bunch of the smaller ones.  Drove more or less as
the crow flies a line between the major airports in the area, with scanner
and analyzer running in the car.  After six hours I heard many very clear
5/5 communications of aircraft, and whole bunch of noisy ones, but none of
the interference, and no pilot in that time complained.  The problem is not
there on the ground.  But sporadic complaints do come in.  The FCC and FAA
are all of a sudden being coy as well.
 
One interesting angle is that the complaints are coming from aircraft at

>10,000'.  Even FAA admits, no ground controller has heard the interference

that the pilots report, when on the same freq.  Most of the complaints have
been 'on approach', if that sheds any light.  This adds to my suspicion that
the problem is aircraft receiver based, not broadcast transmitter related.
 
Also, the comment was made by someone that sychronous AM from FM transmitter
could generate VHF spur in aircraft band.  Ok, perhaps, But in this case,
the interference reported is NOT an IM product.  The nearest product is
300kHz away, and unlikely to occur.  I have done that math, including
allowance for HD carriers mix, and no number equates.  Furthermore, the
complaint is such that were said synchronous AM product occuring, I would
for sure see it on the analyzer, and again would expect to hear it on the
ground and see its appearance in transmitter readings.  
 
I am suspecting something has changed in what is commonly used in aircraft.
Note that proximity to the broadcast tower is not a factor.
 
Reply off list is fine.
 
Thank you


Edwin Bukont CTS, CSRE/DRB, CBNT 
V- 240.417.2475 (DC/Baltimore)
V- 615-357-7390 (Nashville)
 










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