MGL Avionics User Forum

Have a V16, MX1 razor head for redundancy, prefabricated harnesses, insulated jacks,, grounds all run to common ground bar on firewall, all metal airplane...Sonex B. Checked the wiring terminations all good. Have severe interference in the headset when the engine is on...seems clear when the engine is off. The same result on both, igntion 1 or 2. Not sure where to begin looking and would appreciate any suggestions.

Thank you,

Peter
Doylestown Pa

If a 912, I would first be suspicious of the rectifier/regulator- they can be very noisy.
Simplest test is to disconnect the charging line from rect/reg to battery positive and see if the interference goes away.
Fix is to fit a BIG 47,000uF 50V electrolytic capacitor across the rect/reg output and ground.
Use solid wiring (AWG14) and short wire runs as close as pracical to the rect/reg.

Sonex would most likely be a VW derivative.
Make sure you are using resistor spark plugs - straight plugs generate a lot of signal as the current flow through the spark wires is pretty high as the spark fires.
If using electronic ignition systems - make sure these are grounded directly to the engine block with a SHORT connection - in fact they should preferably be mounted on the engine block itself. That ground wire must really be short - the same current that goes via the spark travels through that wire !!
If you are using separate ignition coils the above goes for the coils - grounding is everything here - do not accidentally create a lovely transmitting antenna for that sharp current pulse every time a spark fires.

From another similar case I just got reminded of

Please ensure that your microphone and headset sockets are isolated from the airframe (which normally is grounded and should be) and also isolated from each other. If this is not done there is ample opportunity for errant ground currents originating from ignition and charging systems to add themselves to your microphone inputs via the ground connection at the connectors if not isolated.

Hey Peter,

I had something possibly similar. My V16 is run though an A16 using the digital interface so they act almost like a V16 standalone (with some extra features). It turned out that the microphone gain was waaaaay too high, mostly because on the iEFIS the master volume for the A16 was not obvious to me and was set too low for me to hear. On the ground it was OK, but as soon as I took off the noise was epic. Make sure the main volume is turned up and the mic gain (sensitivity) is down as low as possible. When I did this all the noise went away.

Gareth.

Unplug your microphone. If the noise goes away, reduce the gain.

Regardless of if you have a Razor A16, Razor V16 (with the A16 control added) or are controlling the A16 via EFIS, you have a nice "signal check" in the menu - for each of the ordinary inputs as well as each of the microphone inputs.

This takes the form of a bargraph showing the current signal level and a red marker you should not exceed. So for the microhones, select the desired microphone and look at the bargraph and talk into the thing as you would normally. Then simply adjust the microphone input gain until it "looks right".

You do this with any of the A16 inputs like this (NAV, Music etc).

Now you use the volume control to adjust EVERYTHING except the radio RX (which comes through the COM inputs). Radio RX has it's own volume control allowing you to temporary turn the radio down without affecting the intercom.

Using the digital link indeed marries the A16 (or A14) to the V16 in a way that the two become one. The A16/A14 simply replacing the intercom and PTT functionality of the V16 transparently. Now you don't have to fiddle with audio levels between the V16 and A16/A14 - it's now fixed and optimum.

The digital link provides further significant advantages as no RF can travel in a "destructive" fashion over this link. In general it greatly eases the integration of a complex audio system and VHF radio avoiding much of the potential sensitivity to RF feedback issues during transmit. Your transmissions get the full benefit of high quality audio modulation - the V16 tends to sound really good. Also during receive there is no degradation of the sound due to the additional intercom circuitry and audio wiring as there is no analog audio connection anywhere until the final output amplifier for the headsets in the A16/A14.