MGL Avionics User Forum

When the LCD screen on my iCOM quit working and they wouldn't repair any product over 10 years old, I decided to replace it with an MGL. I have a couple other MGL products that I really like so this seemed like a natural choice. I liked the idea of having the remote transceiver located behind the rear bulkhead allowing a much shorter antenna cable run. This location meant I had to run new wiring back to the transceiver and take out all the old wiring from the previous panel mounted radio. I bought new shielded, twisted pair wire and routed it away from all antenna wires. I am not running an audio panel. I didn't disconnect the headset jacks, simply re-routed the radio end to the rear of the plane, as the wire is good quality shielded twisted pair. They worked fine before so I don't think they would be causing a problem now.

When I turned on the radio for the first time it sounded amazing. After becoming familiar with the operation, I pulled the plane out of the hanger and started the engine. There was complete static that varied in direct correlation with the engine RPM. My battery is located behind the rear bulkhead. After some research I decided to install a capacitor at the alternator positive terminal to ground. I read the battery absorbs a/c voltage and since my positive buss is supplied at a point before the electricity from the alternator reaches the battery, this is supposed to send the A/C back to the alternator before it reaches the radio. I could not find much specific info about what the specifications of the capacitor should be, my friend had a 2500 micro ferad, 25 volt, so we gave that a try.

If anyone has a recommendation for the microferad and voltage rating please let me know. I see Michigan avionics sells a 10,000 mf, but there is no description for it's proper application.

When I started up the static was gone but there was now a ticking noise every second. I tried a run up and the static returned at rpm's over 1600. This was so severe there was no way I could fly until it was fixed. I eventually found if I moved the passenger headset/mic further away, or unplugged it, the ticking stopped.

The only wires that weren't shielded were the power and ground supply to the V16, which in the installation manual are not shown as shielded. I swapped those out for a shielded, twisted pair which took 4 hours to remove the necessary panels and seats etc. to install it and remove to unshielded wires.

That did make an improvement! Finally I was able to do a take off run, but had to abort when the static was overwhelming at that high of an rpm. The default Vox setting is 1. I had been trying it at 3. I was making all the adjustments while sitting in the hanger with the engine off, or while idling in the run up area. I finally found a minimum setting of 7 or sometimes 8 is necessary to get rid of the static because evidently both pilot and passenger mics were opening due to the increased cockpit noise at higher rpm. This seems high to me. Is this normal?

The default mic gain is 0. I've messed with that setting in both directions (-7 to +7) until the sound quality deteriorates but the sidetone is of unacceptably low volume while in flight. I've tried both David Clark and Bose headsets to no avail.
I've read and re-read the installation manual probably a dozen times. It's written at a highly technical level with assumptions made that the reader understands abbreviations like rx, vox, ic, sq, TX. An example: "Here, some of the modulated signal may be demodulated by non-linearities in the system, particularly if the received RF is very strong (typically several volts). I didn't follow that.

I've tried changing the mic filter setting. Default is normal, I can't tell what difference it makes on other settings.

I'm using the modulator setting.
I hear no difference when changing the Rx squelch setting from fast to slow, so I have it set on slow like the default.
I have aux turned off. My gear warning announcement still comes through with deafening loudness.

Other pilots have reported my transmissions are loud and clear, and I don't hear any static or whine when I broadcast. The SWR is 1.2.

I need to be able to hear my own voice at the same level as the intercalm when I talk and it needs to be clear. I've been messing with this for 4 weeks and just want to go fly.

From your description I must assume that your audio wiring to your headset (sockets) is highly suspect - did you insulate your headset and microphone sockets from your panel or mounting location (if metal) ?
Did you use shielded wiring as shown in the diagrams and are the shields NOT used as signal returns (i.e. the shields are connected on one end only and cannot conduct a signal (your signal ground then runs in its own wire inside the shield).

I've read that not insulating the headset jacks is a common problem. I've triple checked that. Mine are mounted in a small metal box that is suspended from the steel cage by insulated Adel clamps. All 4 jacks have fiber washers on both sides of the sheet metal they pass through. The end of the shielding at the jacks is not connected to anything, and has shrink tubing over it to prevent it from touching anything. The other end of the shielding is joined to the other shields at the v16. No signal is running through the shielding. Each mic has its own shielded twisted pair, and the phones jacks use the same shielded twisted pair via a jumper from one to the other. The entire installation is shielded twisted pairs with one conductor being signal and the other being ground.

How can I increase the sidetone volume?

What size capacitor should I be using at the alternator?

Is a Vox setting of 7 or 8 typical? If I set it any lower the mic opens up due to cockpit noise.

Try significantly reducing the mic gains on both P1/P2. -12dB might be a good starting point.

....also, the capacitor value usually needs to be a minimum of 22,000uF 25V.

Serious audio noise issues as reported here are not fixed by fiddling with settings.

Please have a good look at your audio headset/microphone wiring with reference to the manual and ensure you wire it exactly as prescribed.

If you have power supply noise affecting your radio - you have a VERY poor power supply - DC with a lot of noise overlaid at high frequency (audio frequency range). Please connect an oscilloscope to your power supply and view the AC content of your supply once you start the engine.
If you see ignition pulses or AC related to RPM from your generator/alternator please investigate why - on a good installation the supply is clean as it should be.

Your V16 already includes a power supply filter which uses a hefty inductor and two 1000uF capacitors. If power supply noise so high that this filter is overwhelmed you really have a problem that must be fixed. It will affect other electronics you may have in your aircraft as well.

Do not underestimate the power smoothing effect of the aircraft battery - in particular if you install your battery far away from the engine (for example to help with weight and balance. Your battery acts as a gigantic capacitor. If this is the case - your alternator should be isolated from ground and its feeds go to the battery where ever it is - then you have ground and DC cables coming back from the battery to you busbars (so all current on both rails goes via the battery). Yes that may mean you need thick cables to run your starter motor due to the high currents needed. Never, under no circumstances ever use your airframe as ground current conductor. You can do that in cars (with steel chassis) but in an aircraft this is strictly a no-no. You have two huge problems if you do that - the first is galvanic corrosion of the airframe and the second is turning the airframe into a huge antenna to radiate even the tiniest AC signal present on your various grounds.