SonexBuilders.net

I have 2 questions:

1. I have a Microair 760 Rev N radio which I have used for about 12 years. It has developed a problem where I cannot turn down the squelch to an acceptable level. What is interesting is that it is noise free on some channels, and full of noise on other channels. Further, it is intermittent - though getting worse as time passes. I have put ferrite cores on the power leads. I do have a GRT Mini X. Perhaps that is creating the noise. Any advice?

2.If a solution cannot be found for my radio, I am considering replacing it with a Flightline 760. Will this radio fit in the slanted panel of the Legacy Sonex? Any further comments on this radio?

Thanks!

Mervn Friesen
Sonex C-FMNX
370 hours
Jab 2200

The FL760 fits fine in the slanted panel. Have one installed in my Waiex for 6 years... no problems. PM sent.

Hi mervn, I resurected one of these little radios form a salvage yard, and one thing I did was to clean the potentiometers prior to firing it up. One would have to take the cover off, and if you are not able to do that without the proper authority, have the avionics pro clean both pots (potentiometers) with electronic component cleaner spray that is compatable with plastics. dont flood the pot, but just a couple of spritz while rotating the knob end to end. look for any opening around the circumfrence of the pot and that is where you should aim.Otherwise, there may be an adjustment needed to reballance the squelch circuits. 12 years appears to be a long time without problems!Let us know if that helps!

Thanks for your replies. I did further testing of the problem. I disconnected the power cable from the GRT Mini X and the radio was perfectly quiet. I conclude that the noise is coming from the EFIS, and not a fault of the radio.

I found a discussion of the problem on the Van's RV Forum. http://www.vansairforce.com/community/a ... 25808.html There are several suggestions that are worth trying including grounding the case of the EFIS, combining the grounds of the magnetometer and EFIS on pins 7 and 12, and having the A board modified to the more recent B board specs.

I sent an email to GRT and hope that they will assist quickly in finding a solution to this problem.

Mervin Friesen

Good job on elliminating the radio as the problem! What I did while building was to include a common groung buss, grounded to same place as firewall fwd ground on engine block with a #4 cable. Then grounded all items to ground buss, located under the pannel. Also put very larg cap (10,000mfd/50v dc) in parallel (across) plus 12v buss and ground buss to elliminate any extranious noise on the electrical system. Lastly, I made very sure the com antenna had a great ground at its mounting point, even to the extent of using starlock washers under the nut/nuts. Last suggestion, turn everything on with the antenna disconnected from the radio. Noise present=noise via power system; noise gone= noise being radiated and comming thru antenna. Treatments are a bit different, but common ground point to all electrical items may be an answer. I like the idea of seperately grounding the cases of EFIS and all other items.Be sure to go to common groung point directly from each item; dont 'daisey chain' the grounds. Strip the braid off some RG-58c for those straps. That braid is very flexable and is probably tinned so soldering lugs on it would be easy, and has much better 'RF" grounding charistics than just a straight wire.Let all know how this approach works!

I went from a Micro-Air 760 recently, to a Flightline760. I have the legacy Waiex with the slanted panel and it was a direct swap.
The Flightline although less expensive has been a nice improvement in quiet reception and transmit. I highly recommend this unit.
The only thing I haven't figured out yet is how to get the intercom quiet when two headsets are plugged in. No noise when transmitting or receiving but noise when talking back and forth to a passenger. I'm using the 403C intercom instead of the built in intercom. I have the internal intercom turned down to zero.
All in all very happy. Easily listen to chatter 80 miles away and have no trouble talking to anyone within 25 miles.

Larry

Thank you for the continued advice, ideas, and recommendations. I continued to investigate the noise this morning. I took one part of the advice and grounded the aluminum case of the to the dedicated ground buss. I used the wire shield as recommended by Joe Nelson in a previous post. (Great idea!) I flew for an hour without any squelch noise. It was beautifully calm and an enjoyable flight.

I received an email from Mark Allen from GRT after my flight. He suggested adding a ferrite coil on the wires, with the wire looped once. I already have 2 ferrite coils on that line, but will reconfigure them with a coil.

A further explanation for Joe - I built my airplane as you suggest with a separate ground buss and all ground wires running to the buss. I did not however add the big capacitor. Beyond the noise created by the EFIS, my system works very well.

I continue to be hopeful that we can conquer the noise permanently. I hope this discussion is also of value to others.

Mervin Friesen

My two cents. Worth far less.

After three years chasing noise with my FL-760 and adding a capacitor, trying ferrite beads, and adjusting every setting I could....it was my microphone.

Tried a cheap headset with a mic muff from Oregon Aero. Problem solved.

My point - don’t overlook the little stuff. Try a different headset.

Now that is a great idea! hadnt thought of that. I use an external intercom with seperate vol and squelch adjustments, and didnt have that problem. Good catch!!

LarryEWaiex121 wrote:I went from a Micro-Air 760 recently, to a Flightline760. I have the legacy Waiex with the slanted panel and it was a direct swap.
The Flightline although less expensive has been a nice improvement in quiet reception and transmit. I highly recommend this unit.
The only thing I haven't figured out yet is how to get the intercom quiet when two headsets are plugged in. No noise when transmitting or receiving but noise when talking back and forth to a passenger. I'm using the 403C intercom instead of the built in intercom. I have the internal intercom turned down to zero.
All in all very happy. Easily listen to chatter 80 miles away and have no trouble talking to anyone within 25 miles.

Larry

I have a Micro-Air 760 and the 403 intercom and also have the problem of noise on the intercom when talking to a passenger. Noise is acceptable while making transmissions.
Things I have tried so far:
Four different types of headsets
Sound damping in the cockpit to try to minimize noise
Exhaust mufflers to try to minimize noise

If anyone has any ideas I'd love to hear them.

Peter