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Question
I fly an experimental Rans S 16. I have a lot of static on my com especially on approach freq. 135.45. A bench test found the com OK. I find that even on the ground, motor off, nothing on except the avonics, even the transponder is off that I still have this static sound. Should I replace the coax and belly whip antenna?

Answer
This can be a frustrating problem caused by something simple or complex. Let me start with a story? A customer had a Cessna 210 that had this problem on takeoff, sometimes.  I tried everything I could think of. When he went to demonstrate the aircraft to sell naturally it happened again. Since everything short of replacing the coax was done, he suggested to replace the cable and antennas. It was an improperly assembled connector that was found when they were removed to be use on the new coax.  It was the resonate frequency at some takeoff RPM that caused it. Since yours is a static problem (No vibration) You need to look for corrosion somewhere in the power source. An oscilliscope is needed to look at the all the DC lines. I once found it was caused by the bluish corrosion built up on a battery post. Have you tried tuning that frequency (135.45) at another airport or location? Since there are many reasons for this I will ask if you tried switching frequencies on any other electronic devices. Oscillators from other devices can cause this also. Assume you disconnected the antenna to see if the problem stopped? This will let you know if it is picking up the noise from the ambient aera and not from the power source. Try connecting an external antenna. One last suggestion Can you swap radios from another aircraft at your location to see if the problem follows the radio. This will prove it's the aircraft. Would be interesting to see the type of noise, white , pink or random.

Aerospace/Aviation

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Marc Ebelini

Expertise

Basis aircraft and engine maintenance. Avionics and other electronic questions related to computers and radio communications.

Experience

FAA licensed comercial pilot, A&P mechanic, former authorized inspector, ground instructor certified in aircraft, powerplant and radio navigation. FCC commercial license.

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