Expert: Marc Ebelini - 5/18/2009

Question
Hi.  I have a 1964 Cessna 172 with a King KX-170B xcvr and a COM 120 xcvr.  I was in the air when I started experiencing severe static on receive so that I could not understand ATIS, a burst of static with each pulse of my strobe light and a drastic reduction in transmit range on both xcvrs.  Any ideas?
Thanks

Answer
If problem has just surfaced then you are looking at a failure of a component. Since I don't know how your radio's are installed I will have to ask twenty questions. Not really just figure of speech. If it occurs on both radios? Do they have a common antenna? A common ground to the antenna shields may be broken or open is one cause. The strobe may have a failed line filter that allows the noise to get into the DC line. Could also be a open ground in the alternator if you have one or in the generator. Troubleshooting this problem may require isolation. The range of an ADF was very limited. It bench checked good so we went as far as disconnecting the generator off the DC buss. No luck. In desperation the belt drive was removed from the generator. Bingo! It was a bad generator internal ground.
Noise would not normally reduced transmission range but does your power source still produce a clean 14 DC. Little things like a corroded battery terminal can cause these types of problem. Especially if the corrosion has a bluish look to it. That can act like a noise diode. In the example with the ADF. No stone should be left unturned. While it could be the failure in the strobe circuit that may have only compounded another source.
So start by opening the strobe CB, Problem gone then you have your problem culprit. If not, pop the generator CB. If not then do a antenna check with a SWR bridge. I doubt the problem are the radios.
Do some of those checks and let me know if you need more detailed info