What Noise Filter should I get for the alternator on a 84 J model?

[Speed Merchant]

Hi

I recently had a IFR currency check. The instructor I was flying with said that I really need a new noise filter on the alternator. Which one should I get?

thanks!

[N201MKTurbo]

Noise filters rarely fix the problem. If you hear alternator whine in your radios, you either have a failing alternator or bad grounding in your audio system.

[PT20J]

Mooney J uses a sealed pi filter module (series inductor and two caps to ground) an an external large aluminum electrolytic capacitor. The parts are in the Service Manual and shown in the schematic. 

However, I agree with @N201MKTurbo that there is not much there to go bad and that’s probably not your problem. 

[0TreeLemur]

What audio panel do you have?   If it is an older one that might be your problem.  New ones sold today filter noise very well.

[Speed Merchant]

On 7/1/2023 at 1:25 PM, 0TreeLemur said:

What audio panel do you have?   If it is an older one that might be your problem.  New ones sold today filter noise very well.

I have a Garmin 750xi with a built in audio panel. Radio transmission and receiving are weak and with lots of static at the end of the transmissions. I am not sure what the issues is. I was told a noise filter would help. I had the 750xi and a 355 installed about two years ago. The audio with both units leaves a lot to be desired. I have had ATC contact me through other planes on the freq because either I couldn't transmit or receive 3 or 4 times.I have brought the plane back to the shop that did the install and they say there is nothing wrong with it. Very frustrated. Suggestions appreciated.

Curt

[Speed Merchant]

On 6/30/2023 at 11:18 AM, N201MKTurbo said:

Noise filters rarely fix the problem. If you hear alternator whine in your radios, you either have a failing alternator or bad grounding in your audio system.

I really don't hear a whine- lots of static at the end of transmissions. If it isn't the filter what might it be?

thanks

[Fly Boomer]

16 minutes ago, Speed Merchant said:

I have a Garmin 750xi with a built in audio panel. Radio transmission and receiving are weak and with lots of static at the end of the transmissions. I am not sure what the issues is. I was told a noise filter would help. I had the 750xi and a 355 installed about two years ago. The audio with both units leaves a lot to be desired. I have had ATC contact me through other planes on the freq because either I couldn't transmit or receive 3 or 4 times.I have brought the plane back to the shop that did the install and they say there is nothing wrong with it. Very frustrated. Suggestions appreciated.

Curt

With that equipment, you should have zero problems.  Take it to an avionics shop.

[EricJ]

27 minutes ago, Speed Merchant said:

I really don't hear a whine- lots of static at the end of transmissions. If it isn't the filter what might it be?

thanks

Do you mean there's a brief period of static at the end of transmitted or received messages?   That may just be a delay in the automatic squelch circuit or the rx/tx switch.

[Speed Merchant]

14 minutes ago, EricJ said:

Do you mean there's a brief period of static at the end of transmitted or received messages?   That may just be a delay in the automatic squelch circuit or the rx/tx switch.

Yea there is a brief period of static. Very annoying. Is the automatic squelch circuit adjustable? I was told that at the end of the transmission it goes to full squelch. But the transmissions are still weak- could that be related?

[hubcap]

I had a similar issue, it required replacing the original 41 year old antenna. Problem solved.

[Bartman]

Not all “antenna problems” are really the antenna. In my thread from about 5 years ago I documented replacement of the retro 7 antenna with the CI-196 along with new RG-400 cable. In the last post I mentioned clear reception on one mag and static on the other and that was the clue to the answer. We did have the dual mag serviced but the problem remained. After replacing my magneto cap and spark plug wires my problem vanished. Ultimately it was RF interference from bad spark plug wires and worked great even with the old antenna. I was already committed and installed the new antenna to replace the 40 year old one. No transmission or reception problems since. 

[Bartman]

Continuation from my post above…..Try an in flight magneto check and see if your problem resolves on either the left or right mag. 

[Speed Merchant]

On 7/5/2023 at 8:54 AM, Bartman said:

Not all “antenna problems” are really the antenna. In my thread from about 5 years ago I documented replacement of the retro 7 antenna with the CI-196 along with new RG-400 cable. In the last post I mentioned clear reception on one mag and static on the other and that was the clue to the answer. We did have the dual mag serviced but the problem remained. After replacing my magneto cap and spark plug wires my problem vanished. Ultimately it was RF interference from bad spark plug wires and worked great even with the old antenna. I was already committed and installed the new antenna to replace the 40 year old one. No transmission or reception problems since. 

I am bringing my bird to Sarasota Avionics to have the problem resolved. Thank you for your post.

[Will.iam]

4 hours ago, Speed Merchant said:

I am bringing my bird to Sarasota Avionics to have the problem resolved. Thank you for your post.

You might want to test the mags first before the antenna like bartman above posted. Or fly to a field that has a tower, land and goto a parking spot. Shutdown the engine and on battery power talk to ground. If it’s clear, you know it’s not your antenna Or cabling to the antenna and that will save you from replacing something that will not fix the issue. 

[Speed Merchant]

On 7/4/2023 at 7:39 PM, Speed Merchant said:

I have a Garmin 750xi with a built in audio panel. Radio transmission and receiving are weak and with lots of static at the end of the transmissions. I am not sure what the issues is. I was told a noise filter would help. I had the 750xi and a 355 installed about two years ago. The audio with both units leaves a lot to be desired. I have had ATC contact me through other planes on the freq because either I couldn't transmit or receive 3 or 4 times.I have brought the plane back to the shop that did the install and they say there is nothing wrong with it. Very frustrated. Suggestions appreciated.

Curt

I finally resolved my poor transmission and reception problems with my 750xi and my 355. It turns out the the mic gain was not set correctly. One two minute adjustment and everything is good now. The range is much better and I feel like I can contact France now from Vero Beach. It sounds like it should of been an obvious thing to check. I contacted three avionics shops about my issues before it was taken care of.