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Avionics Question.?

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What would cause a aircraft radio to have problems being heard on the ground by ground control, but in the air it could be heard for 10-20 Miles with no problems?

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  1. Yes, antenna location on the aircraft and the proximity of ground structures can hugely affect the way a radio will transmit on the ground. Quite often the antenna location won't have any (or very little) effect in the air. Most antennas do not radiate transmitted energy equally in all directions (this depends on design, positioning, and grounding), and this directionality is often only apparent when you are very close to the tower or other receiving station. Such problems are particularly true of Com antennas mounted on the belly of an aircraft. Orientation of the aircraft to the receiving antenna is also a big factor too, particularly for antennas not located near the center of mass of the airplane.  Also, if the plane has a generator as opposed to an alternator, the system may not be generating full voltage when the engine is idling, which can also lead to radio problems.


  2. Is you aircraft Generator powered or Alternator?  If its generators, then you have a BATTERY problem which lowers the radio voltage and keeps you from having good power to the radio at LOW RPM!  (Been there done that!)

    When you are flying the RPMs will produce enough Generator voltage to keep the radios working correctly. At low RPM the voltage output is much lower and the battery has to supply the voltage.  

    The power available to drive the radios is critical.

  3. Sounds like you have a similar frequency interfering at ground level, try changing the frequency band.

  4. Good question. Maybe ground control was using a ground plane type antenna and you were well below the best angle of radiation while on the ground nearby? Was your engine  running and the alternator producing power while you were on the ground? Did ground control have the squelch set too high to hear you? Sorry I can't give you an answer, only more questions.

  5. depends on the frequency, weather etc. attenuation can be quite a problem.

  6. A blocked signal is the best reason as was mentioned.  Often on airplanes with 2 radios one antenna will be on the belly and the other on top of the fuselage.  It's common for the belly mounted antenna to have a lot of problems on the ground because of the location of the antenna and how bad the signal is so close to the ground.  

    If this is in fact a panel mounted radio and your range is only 10-20 miles in the air you probably have more serious problems- I'd probably have that checked out in an avionics shop (could be an antenna problem, a static problem, or a radio problem to name a few).  20 mile radio range is not impressive by any means.
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