What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Comm Static...

Piper J3

Well Known Member
I have a FlightCom 403 intercom in my RV-12. Recently I have been getting static on the SL40 comm and also when using the intercom itself. If I toggle the intercom switch to the ?isolate? the comm radio has crisp reception.

My question? if I place the 403 in ?isolate? does that essentially remove the intercom and run the comm radio direct? In other words ? does it seem the problem is in the intercom itself?
 
It sounds like the static is coming from the copilot jacks. Remove hem from the panel and let them hang without touching each other and see if the static goes away. The isolate feature basically removes the copilot from the system.
 
Thanks. I'm going to try removing the copilot headset and try another headset in its place. If that doesn't fix it I'll look at jacks and wiring.
 
It could also be the copilot headset, if plugged in, breaking squelch. It depends on what type of static it is.
 
antenna

Seems unlikely in this case, but just this past weekend I helped out an RV12 builder with a very bad Comm static problem. It was intermittent. He had redone the headset jacks and thought it was fixed.... Long story short, I pulled the panel on the belly, left side, next to comm antenna. I disconnected the antenna cable and the BNC connector came off the cable in my hand. We then checked the cable coming out of the radio itself. Same thing. I put new BNC connectors on the cable and the problem appears to be fixed.

He (the builder) told me the cable had come from Van's. It was definitely not crimped properly, but it was crimped, just not properly. A very light "pull test" and the connector came right off.

As an aside, searching for the same problem last weekend, we discovered an error in the pin-out of the harness coming out of the fuse box. The result was that several of the fuses were in parallel. I felt this to be a serious problem, which we fixed. He reported to Van's and they said it was a known issue with the harness from some period of time and that it was still airworthy with the error. Personally, I disagree with that. There was essentially no protection on a wire that shorts since the current would be divided between the fuses, etc.

Simple test to see if this affects your airplane. Turn everything on including the radio. Then pull the comm fuse. If the radio stays on, you have one of these bad harnesses.

Coincidentally, the radio static cleared when we corrected this so I thought maybe it had just been a weird RF grounding path issue. What really happened was that our monkeying with the fuse panel, we shook things enough so that the bad antenna connectors made proper contact temporarily.

Sorry for the long note. Just thought on the off chance you were fighting the same root issue, this might help.

-Joe
 
Thanks for the tips guys...

Today I will try to sort this problem. I'll check harness wiring as Joe suggests. I have early SN RV-12 so may be affected.

Two years ago I had similar problem and turned out to be the FlightCom 403 itself. A screw holding a heatsink came loose and was shorting the circuit board. See http://www.vansairforce.com/community/showpost.php?p=1075672&postcount=1.

My current problem is exaggerated in flight. Comm radio and intercom both work good on the ground and during taxi but get static in flight as mentioned in my first post. If memory serves, that is same symptom when screw came loose in the 403 the last time. In my opinion the 403 is susceptible to having the heatsink screw vibrate loose over time and design needs to be improved.
 
Just got back from morning flight to sort comm static issue and can report some observations…

• Comm fuse is wired correctly by Joe’s tests so that’s a load off. Thanks Joe.
• Disconnecting copilot headset has no affect on static
• Isolate switch on FlightCom 403 does indeed solve static problem
• Reducing squelch by about 20 degrees CCW knob rotation also solves static problem. At this squelch setting there is no difference between isolate/all switch positions on the 403 – both are identical and static free. However, at this retarded squelch setting initial voice doesn’t trigger the VOX for the intercom very well and start of first word gets clipped off.

Question – perhaps some of the tunable settings in the Garmin SL40 comm need to be revisited. It sure seems like the mic noise (at squelch threshold) is somehow breaking through to the comm receive signal. I base this on listening to an AWOS being repeated and playing with the FlightCom 403 squelch setting. Lower squelch on the FlightCom 403 reduces static on the comm and also static on the intercom itself. Does that make any sense?

Any help appreciated…
 
Sounds like it could be the pilot?s headset breaking squelch. When you isolate, can you still talk and hear yourself? If not, then this could be the problem. Try a different headset and make sure you have a mic muff on your headset.
 
Sounds like it could be the pilot?s headset breaking squelch. When you isolate, can you still talk and hear yourself? If not, then this could be the problem. Try a different headset and make sure you have a mic muff on your headset.

Yes, when I isolate I can still hear myself and I can also transmit voice in isolate.
 
if you have anything plugged into a power receptical, unplug it and try again. Cheap usb phone chargers are noisy, and open my squelch.

Jeff
 
Do your checks with the radio *off*. If the radio is breaking (RF) squelch, it'll muddy the waters in your troubleshooting. Turning it off will either eliminate it as the problem, or (potentially) define it as the problem.

The intercom's squelch (VOX) circuit should not affect audio from the radio; the radio's RF squelch circuit handles RF noise muting.

Having headset mic gain set too high can cause all sorts of squelch issues, especially in a noisy a/c. If the gain is set too high, it's constantly trying to trip the intercom's squelch circuit due to ambient noise. If you reduce the mic gain, the system signal to noise improves because your voice will be louder than the ambient noise. Too much mic gain can also overdrive the input circuit in the intercom, making for fuzzy, distorted sound.

Most electret condenser mics used in modern headsets have a gain adjust trim pot in the mic housing itself. Look for a small (<1/8") hole somewhere on the mic housing. Most have a slotted head in the hole, adjustable with a jeweler's screwdriver.

Charlie
 
Does anyone know the default Test Mode values for Gramin SL40? These are values for:

? Receiver Squelch
? Mic 1 Level and Mic 2 level

The values are accessed by pressing and holding the <> and RCL keys while switching unit on to enter Test Mode
 
I pretty much fixed my static problem. I made adjustments to both System Settings and settings in Test Mode. I contacted Garmin for the default factory settings for Test Mode as follows:

RCVR SQELCH 065
MIC 1 LEVEL 255
MIC 2 LEVEL 255

Thanks for everyone's help...
 
Back
Top