[SBE] Aircraft radios.. cross posted

[Lotus Engineering]

This is a common problem with some aircraft radios and has been for several years.  Another hat I wear is deputy director of communications, NV wing Civil Air Patrol.  Some of our planes, flying close to high power FM transmitters get front end overload.  When I was in Tucson, a common complaint came in from aircraft flying past the Tucson Mt. Site on final for the Tucson international airport.  For all the money that aircraft radios cost you'd think they would have better front ends, but that is not the case.  At least one case was found to be common RFI being picked up by the wiring to the aircraft intercom system.  If you are clean, the FAA technicians are usually reasonable.  I am unaware of any major changes in Aircraft radio technology that would account for this.
Bill

Lt. Col. Bill Croghan, CAP

WBØKSW, CPBE

Las Vegas, NV

Chief Engineer,

Lotus Broadcasting, Las Vegas, NV

KOMP/KXPT/KENO/KBAD/KWWN/KWID





From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org] On Behalf Of Edwin Bukont
Sent: Wednesday, September 26, 2012 4:56 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)










________________________________
Lotus Broadcasting Corporation and radio stations KOMP FM, KXPT FM, KWID FM, KWWN AM, KBAD AM, and KENO AM do not and shall not discriminate, in any way on the basis of race, ethnicity or gender, with respect to our advertising practices.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://seven.pairlist.net/pipermail/sbe/attachments/20120926/63074d11/attachment.htm>