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John;
Great text! I've been using RG400 for any new
install or replacement. Comments, please?
Thanks
Al
----- Original Message -----From: John SilbermanSent: Monday, September 04, 2006 9:42 PMSubject: Re: [COUPERS-TECH] Radio or Antenna "bleed over"Chad,
The problem is in the "front end" or RF section of the receiver. All radios are not designed alike. So just will not reject very high power stations. I'll bet you only get it at your airport but it's fine at most all other. And, the radio shop would find no problem since they test into a dummy load instead of an antenna and a signal generator instead of the real world. The offending signal may not be even in the aircraft band. It is generated in your set by mixing with the local oscillator. You have to stop that signal from reaching your radio. If the signal is coming in through the antenna, you will need a band pass filter for the aircraft band and it will clear up. If it is coming in through the radio itself, make sure the radio is solidly grounded to the aircraft. If it is coming in through the 12 volt line, you will have to run the 12 v through a torroid several times to keep it from entering that way.
Suggestions:
1. Make sure it's overload/intermodulation. I'd bet if you depart the airport in a different direction the problem disappears faster. Beside the microwave tower, look for towers near the airport and fly near them - be careful don't have to be THAT close- and see if the problem occurs or gets worse.
2. Make sure all the grounds in the aircraft radio system are secure. Check the coax cable at the antenna. Remove it from the antenna and check it for corrosion, check the braid is not broken at the connector. If you're using a stick antenna, remove the coax ground from the screw to the skin and clean the area, screw and coax cable, reattach. Then do the same to the wire on the antenna. If you take them both off together, the inner conductor goes to the antenna. Make sure the coax is secure at the radio end. Most problems are caused by old, kinked, ungrounded cable or a bad antenna. If you have to replace the coax, most places replace it with the same RG-58. This coax is very lossy it 120 Mhz ( I love it when they use it on transponders and DMEs 1000 Mhz you lose half you transmit power and receive signal between the unit and the antenna) Use RG-8X, it's got the same properties except it is very slightly thicker - almost unnoticeable. and it is much less lossy. Do not use Radio Trash cable. It has about 85% shield and you WILL get stray signals and noise through it. Go to a proper supply house and get a 95-100% braid cable. Good names are Belden and Times. Do not use used cable no matter how good it looks.
Keep me informed.
jsilberman
After that, if you still have the problem, let me know and I'll give you more steps.
On Sep 4, 2006, at 6:17 PM, CHAD SURMICK wrote:
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Greetings,
I have a 1965 Alon A-2 that has had a frequency bleed over problem for a while now. Let me give the group a little history. When I fly within 3-5 miles of a microwave and radio tower near my home airport, STS Santa Rosa, CA., on tower frequency the radio goes complete static, I cannot control the squelch, I can not transmit or receive at all, the tower says I am "scratchy" if they can hear me at all. Once I pass the area, the static goes away and the tower can hear me just fine. The radio has been to the avionics shop and declared healthy, no problems. Could I have 1. corroded contacts in the wiring to the antenna, 2. A bad antenna, 3. Bad Intercom? Its been frustrating as it happens in other parts of the Bay Area when I am near radio towers, specifically on MT. Tamalpais.
Any Ideas?
Thanks in advance.
Chad Surmick
Alon A-2 N5479E
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