L

Lancair Super ES

Well Known Member
Well, I have been flying my Lancair for 80 hours and loving it. Knocking off the last of the minor squawks. One the has me perplexed is a very staticy background noise:

Get it on both radios - a G530 and an SL30, on different antennae
SL 30 is on an exterior Comant 121; G530 is on a bonded in AAE in vertical
My transmissions are heard fine
I actually here transmissions in when it is staticy fairly well most of the time
The WEIRD part is it is 100% reproducible on 118.xx, 119.xx and 120.xx freqs only. Rest of freq spectrum is crystal clear with good range

I thought I had it narrowed down to the Primary ALT since at 8-900 RPM I could switch the static off and on with the field switch. So, I put one of those big capacitors (from B&C) on the PRIM ALT. No improvement at higher RPMs. Noise is the same with either alternator.

Any ideas? The lower freqs only has to be a clue, I just don't know what is means!!

Thanks in advance for any ideas or direction.

Gordon

Lancair ES N144GP
IO-550

VAF paid
 
How is the engine grounded? If you don't have it grounded with a braided ground strap then I suggest changing your ground over to one. The braided straps are of lower impedance at higher frequencies.
 
I had same problem

I recently had the same problem, and it developed after some grass field landings..so, I was suspect of loose connections. I had good volt/amp readings, but noticed during a late evening flight my ALT OUT idiot light was slightly flickering. I have a CAM 40 amp ALT with internal regulator, so I pulled off the 2 connector plug, and found the spade connector for the idiot light was broken in two internally. I quick 5 minute replacement of the connector, and I'm static free and back in business. I hope your find is as simple as mine was.
 
Noise.

Gordon,

What kind of sound are you hearing (whine, whistle, crackle, etc.). Is it audible all the time, or just when you "break squelch?" How about on intercom only/side tone - radios off? Does the noise have a discernible pattern to it?

Thanks!

Brian
 
grounded.... sounds like broken squelch

The engine is grounded to batt ground with a high quality braided strap and to a single ground block. Each circuit in the aircraft is grounded back to a single block.

The dual batteries are in the baggage area so there are 2 fat wires (2 AWG) running back there on the opposite side of where I ran all the antenna wires.

Noise sounds like always open squelch. Have fooled with squelch settings to no avail. No whine or rhythm to it... just open, loud crackling noise.

Thanks for the ideas.

Gordon
 
Have you tried using a handheld radio in your plane? If so, does it have the same problem?

You can also take the handeld and move over your electric lines to try to fimd the offending component.
 
Transmitting or Receiving??

Gordon,

I know how frustrating these problems can be -- and debugging them equally so, like explaining TV to a bushman :)

When the offending noise occurs, is it associated with a transmission being received by you or a transmission being made (which radio), or both? i.e. if you key up to talk, do you hear the crackling on top of or in place of your voice in sidetone? If you're sitting quietly on the ramp at idle, do you hear the noise or does it only happen when someone else in the pattern/on field keys up?

If you have a handheld with you, does it also demonstrate the noise when the noise occurs?

b
 
I had a similar issue with my KIS4 composite airplane. Troubleshooting an issue like this is a PITA, and made even worse in composite aircraft.

First, check ALL your grounds, especially those associated with your audio panel. Make sure they are tight and any crimp is making good contact. If this doesn't fix the problem then, since it happens only on specific frequencies and your transmissions are reported crystal clear, you might have a harmonic entering the audio panel causing the problem. This is much more common in a composite airplane than in a spam can.

If this is the case, no amount of passive filtering will fix the problem. I had to use an active Smothie Brickwall Filter connected only to the audio panel 12v power input. It finally eliminated the noise on the certain frequencies. And, like your problem, mine happened only with my Garmin 430W. It never happened with my Icom A200.

But first, check and double check your grounds especially any crimped ground connection. Good luck and let us know what you find.

:cool:
 
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Do you have any powered GPS antennas on the aircraft other then the Garmin?

I would not expect the Garmin antenna but some of the low cost GPS antennas (Pucks) have been known to self oscillate and cause problems.
 
SL30

Check your NAV button on your SL30. When you push it once you get the ID tone. If you are not within range of the selected VOR or LOC frequency, you will only get an annoying static. If you push the NAV button a second time you will revert back to silencing the ID tone and or static for normal operations.

Good Luck!
 
Thanks for the replies and clues

Thanks to all for the replies and clues. Some asked questions, so I will attempt to answer the ones I can right now:

Grounded with a braided strap to engine
It is a broken squelch sound, on both radios, all the time when on 118-120 freqs
Headset jacks insulated and grounded at audio panel side
Haven't tried using a handheld as a "sniffer" but that will be part of my troubleshooting


GalinHDZ - that Smoothie Brickwall is slick. I read the limited manual of theirs on the website. Do I understand correctly that you put it across a 12v 5A fused circuit and it filters the whole electrical system? Or, does it need to be input to the audio panel specifically?

dpansier - The AFS EFIS has a separate GPS puck, but it is a "ARMIN" ... that is a Garmin with the G scratched off! You seem to be in the antenna business, so perhaps I can pose this question to you? When fabricating the RG400 lines with BNC connectors, is it correct to terminate each end's shield to the BNC itself? I hear about grounding only one end, but not sure how you would really do that and still correctly install and crimp the BNC. Also, the center pin was crimped, but not soldered as I now understand they should be. Would that cause a problem like this?


My next step is to create a written logical troubleshooting plan starting with engine off, turning on things in sequence, moving to engine on idle, then high rpm, then to flight. Many of these things I have already done, but not in a coordinated way. Will recheck all ground connections.

Thanks for the ideas. Will let the group know what I find.

Gordon
 
Lancair Super ES said:
When fabricating the RG400 lines with BNC connectors, is it correct to terminate each end's shield to the BNC itself? I hear about grounding only one end, but not sure how you would really do that and still correctly install and crimp the BNC. Also, the center pin was crimped, but not soldered as I now understand they should be. Would that cause a problem like this?
Click to expand...

Coaxial antenna/RF feed lines that use BNC connectors should have the shield connected to the outside barrel of the BNC. Do not only connect one end like you do with other shielded signal lines.

Some center pins are made to be crimped and some are made to be soldered and some can be both.

Failure to connect both ends of the shield can cause problems.

Failure of the center pin to make good contact to the center conductor can cause problems. Typically however crimping or soldering works fine if done correctly.
 
Lancair Super ES said:
GalinHDZ - that Smoothie Brickwall is slick. I read the limited manual of theirs on the website. Do I understand correctly that you put it across a 12v 5A fused circuit and it filters the whole electrical system? Or, does it need to be input to the audio panel specifically?
Click to expand...

I used it ONLY for audio panel power. It can't handle the current draw of a radio when it transmits.

You also stated that both radio transmissions are crystal clear and it happens only on certain frequencies. This sounds like harmonic frequency(s) somehow entering your audio system. What audio panel do you have?

Brantel said:
Coaxial antenna/RF feed lines that use BNC connectors should have the shield connected to the outside barrel of the BNC. Do not only connect one end like you do with other shielded signal lines.
Click to expand...

Rule of thumb for cable grounds:

If you want to prevent signals from getting OUT of the cable, ground both sides.

If you want to prevent signals from getting IN to the cable, only ground the side closest to the equipment.

:cool:
 
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