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Radio Hum

S

sjespers

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I have developed a background hum on my radio. It is a low frequency sound that increases in pitch as I advance the throttle. I can also hear the pulse landing light as it flashes and the strobe lights when they flash. However, when I transmit or receive on the radio the hum goes away. Do you have any suggestions as to what I should look for?
 
Could be your intercom, not your radio. Turn the radio off; is the hum still there? I also hear the strobes and landing light on pulse very faintly when the engine is not running. So faint I haven't tried to see if it is the intercom or radio.
 
I turned off the avionics switch and the hum continues. With the avionics on I adjusted the volume and squelch and there was no change. I adjusted the squelch and volume on the intercom with no change. Could it be a grounding problem?
 
Quote from SkyView installation manual page 4-23:
To minimize the possibility of audio ?humming?, a 16 AWG wire may optionally be connected between the ground point for the intercom/audio panel/radio(s) and SkyView display case(s). To attach the wire to the SkyView display case, a 4-40 x 3/16? long screw may be screwed into the threaded boss above the USB ports on the back of the SkyView display.
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Quote from the D-180 instaltion manual:
Page 2-2 of the FlightDEK-D180 Installation Guide says, "Because of the current drawn by the FlightDEK-D180, even very small resistances between battery ground and instrument ground can cause voltage differences which adversely affect
engine sensor readings. An easy way to test the quality of the instrument?s ground is to measure voltage between the ground pin at the FlightDEK-D180 and the ground lead at your aircraft?s battery. With the FlightDEK-D180 powered on, connect one lead of your voltmeter to a free ground lead coming from the FlightDEK-D180. Connect the other lead of your voltmeter to the ground terminal of your battery. The voltage between these two points should measure very close to 0 mV (within 5 mV). If it does not, you must improve the ground connection between the ground of your battery and that of your avionics bus."

In the above test, the D-180 case can be used in leu of a ground lead.
Make sure that the battery cable is well grounded to the airframe at the battery box. Make sure that the control board is well grounded to the airframe with a wire and screw per the plans. Make sure that the Dynon D-180 is well grounded to the airframe. There should not be any paint on aluminum at the ground connections. An additional grounding wire could be added to the D-180 EMS 37-pin connector at location 3 or 5 or 13 if desired.
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Quoted from the SkyView System Installation Guide - Revision R, Page 22-1
Grounding
Many of the engine sensors require a connection to a ground on the SV-EMS-220/221. There are many places on an aircraft where you could connect these sensors. However, the ideal location to ground these sensors is to one of the SV-EMS-220/221 ground pins. Connecting the sensor?s ground pin directly to the SV-EMS-220/221 minimizes any voltage difference between sensor ground and SV-EMS-220/221 ground. You can measure the voltage difference between grounds to check if the connection has a minimal voltage drop. Set a multimeter to the DC voltages setting and place one probe tip on one ground and place the other probe tip on the other. Measurements close to 0 mV (within 5 mV) are, in most cases, acceptable. Other grounding recommendations include:
 Ensure that solid, thick electrical connections exist between engine and battery ground.
 Do not paint over surfaces that are ground connection points.
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Below by Joe Gores: The above voltage checks should be done with all electrical devices turned on.
 
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