static on radio

[rstisser]

My 6A has developed a radio problem in the last few days. I have an SL30 comm radio and a Pm3000 intercom. On startup I am getting static on the headphones and it is also being broadcast on the comm radio. The transmit light flickers when this is going on. It seems to clear up after 5-10 minutes and does not reoccur until the next flight. I am not a radio expert and need to call on those of you who are. Randy

[Mike S]

The time sequence leads me to think-------------what electrical noise generating device operates for the first few minutes after starting, then goes away until the next time you start???

Two things come to mind----------starter is hanging up, lets go after a bit, or the alternator/regulator system is working really hard to replenish the battery after start.

Might be a good place to start looking.

One more thought.... if the battery is slowly dieing, the radios etc may be experiencing low voltage issues until after the initial after start recharging is done.

[jcmcdowell]

Would starting the engine up and keep it above idle be a good test of the alternator/battery issue.

Typical startup:
start- rpm 800-1000

would getting the rpm upto 1200-1300 right away to see if you still have the noise provide any indication about the battery/low voltage situation?

Can you isolate the PS intercom to check the static between radios and intercom? Can you turn the radios off and play music through aux music to see if intercom has static separately?

I had a broken ground on the PTT line that caused the transmit indicator to blink and caused A LOT of noise on the pilot side. Is the noise the same on both pilot/copilot sides?? That will help track down from jack/mic per side to intercom issues.

I found my 'noise' in a broken shielded ground wire #24 soldered in a weird angle to a #18 PTT line hidden by heat shrink tubing.

Best of luck.

[rstisser]

Thanks for your reply on the PTT wire. Did your noise stop after a while or continue all the time? Also on the posibility of a alternator or starter caused problem would that cause the radio to broadcast the static? Randy

[jcmcdowell]

I am certainly not an avionics or wiring expert.

My problem was ONLY in the pilot jacks and was intermittent due to a broken ground.

I have to narrow down the possibilities because its too overwhelming too diagnose the whole system.

You can start by determining if the problem is on one jack or both jacks (pilot/copilot).

Is the problem persistent on both PTT lines

Does the problem persist with radios off

Does the problem persist with intercom off (if you can still hear radios)

Does the problem persist under high RPM (alternator producing 14v+/- and charging battery)

Does it only show up on startup cold. Do you get the same problem if you fly for awhile and then shut off the engine and then start back up?

Do you only have static with the engine running- or do you get static with just the alt/mag on and avionics on?

If you can work through the conditions in which the problem ONLY show up you can narrow down the system which might cause the problem.

Another thing- The problem is most often the simplest answer. The natural tendency is to jump to the most complex (or expensive) answer as the problem.

It could simply be a loose ground line on a starter or selenoid.

Best of luck

[rstisser]

I will be going to the airport later today to begin to narrow the possibilities. Thanks for all the ideas. Will post something tonite. Randy

[rstisser]

Well, I spent two hours trying to sort out the static problem yesterday afternoon. No matter what I did I could not make it act up when I wanted it to. I checked everything that I could think of including both PTT connections, all ground and power leads to starter and alt, etc, etc. The PTT switches themselves could be the culprits, but I will have to wait for it to act up again. Unfortunately it acts up a inopportune times like when you are talking to the tower @ Fondulac while taxiing out to runway 18. I am sure it will return. Guess I'll try to fly everyday until it does. Randy

[rstisser]

I thought you might like to know the final resolution of my problem. I began having trouble with the intercom even when the radio was turned off. I called PS Engineering and their tech rep said it had to be an interface problem with the radio. I sent the intercom in to them anyway and they replaced a diode. problem solved. Randy