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Garmin radio has loud white noise when transmitting

P

petersb

Well Known Member
I have a garmin SL40 radio connected through a Garmin 240 audio panel.

Two issues:

Issue One: Loud white noise when PTT pressed.

I have tried different headsets, turned off Garmin 240, reprogrammed sidetone to 000 ( follows volume control), reprogrammed mic gain to lower level.

Although the white noise (hisss) is very loud during transmission others report receiving me at 5 by 5 .

White noise volume is lower at low RPM, it is not alternator whine.
When engine not running white noise is present for only two seconds after PTT pressed.

Issue Two: I can hear nearby AM radio in hanger through headset when PTT pressed.

I double checked grounds to plugs and made sure they where isolated from ground at plug end.

Thoughts please

Peter
 
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Have you installed isolation washers on all headset jacks so that they make no electrical contact with the airframe?
 
krw5927 said:
Have you installed isolation washers on all headset jacks so that they make no electrical contact with the airframe?
Click to expand...

Yes, I have used both the fibre washer and the rubber hat washers and also checked for no continuity between plugs and airframe

Peter
 
petersb said:
I have a garmin SL40 radio connected through a Garmin 240 audio panel.

Two issues:

Issue One: Loud white noise when PTT pressed.

I have tried different headsets, turned off Garmin 240, reprogrammed sidetone to 000 ( follows volume control), reprogrammed mic gain to lower level.

Although the white noise (hisss) is very loud during transmission others report receiving me at 5 by 5 .

White noise volume is lower at low RPM, it is not alternator whine.
When engine not running white noise is present for only two seconds after PTT pressed.

Issue Two: I can hear nearby AM radio in hanger through headset when PTT pressed.

I double checked grounds to plugs and made sure they where isolated from ground at plug end.

Thoughts please

Peter
Click to expand...

Come on guys, no suggestions

Peter
 
I would be looking at radio and IC ground connections (rack plug to ground), also make sure both units are fully seated in the rack (faceplate against tray).
 
Too much system gain...

It may be too much overall ststem gain between the radio, intercom inputs, and your headsets...

Try isolating your volumes and reduce each to make sure that you are not getting an overdriven input.
 
Walt said:
I would be looking at radio and IC ground connections (rack plug to ground), also make sure both units are fully seated in the rack (faceplate against tray).
Click to expand...

Walt

Antenna and plug grounds are connected to rack, power ground is connected to common ground tabs, I do not have a ground from the rack to the ground tabs.

By the way in regards to dynamic prop balance I used your formula for weights and got .007 on the first try. Smoothed out 2300 rpm cruise, but the 2700 takeoff is still quite buzzy

Peter
 
[email protected] said:
It may be too much overall ststem gain between the radio, intercom inputs, and your headsets...

Try isolating your volumes and reduce each to make sure that you are not getting an overdriven input.
Click to expand...

Stephen

I tried with the audio panel/intercom off (Garmin 240) and noise is still there

Peter
 
petersb said:
Walt

Antenna and plug grounds are connected to rack, power ground is connected to common ground tabs, I do not have a ground from the rack to the ground tabs.
Click to expand...

Antenna ground connected to rack? What does that mean?
 
Noise can be a difficult thing to track down, so other than giving general suggestions on what to look for I don't think I can be of much help. Noise and AM radio reception stuff is "generally" caused by improper/bad grounding somewhere.
 
Plug grounds?

If your plug (jack) grounds are also grounded to the rack or ship you will have problems. On some radios the headset and mic grounds go to different pins (and not the ship or rack).

I think you probably wired this correctly and just mis-typed but it's worth re-checking every ground and making sure you are fully isolated between the two jack grounds and all other grounds on your cages, radio, and intercom.

You don't mention if you have 1 or 2 radios. I've had problems with 2 radios on close frequencies with one transmitting and bleeding to the other radio as noise. This did not transmit to others who heard me 5x5.

One other possibility is a floating shield on your mic or headset wiring. Or, a shield that is grounded at both ends. Have you looked at this possibility?
 
AllThumbs said:
If your plug (jack) grounds are also grounded to the rack or ship you will have problems. On some radios the headset and mic grounds go to different pins (and not the ship or rack).

I think you probably wired this correctly and just mis-typed but it's worth re-checking every ground and making sure you are fully isolated between the two jack grounds and all other grounds on your cages, radio, and intercom.

You don't mention if you have 1 or 2 radios. I've had problems with 2 radios on close frequencies with one transmitting and bleeding to the other radio as noise. This did not transmit to others who heard me 5x5.

One other possibility is a floating shield on your mic or headset wiring. Or, a shield that is grounded at both ends. Have you looked at this possibility?
Click to expand...

Per SL40 manual, headphone and mic shields are connected to radio chassis and Garmin 240 chassis. Then from the audio panel to both jacks the shields are only connected at the audio panel chassis

Only one radio connected to audio panel then headset

Peter
 
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petersb said:
Per SL40 manual, headphone and mic shields are connected to radio chassis and Garmin 240 chassis. Then from the audio panel to both jacks the shields are only connected at the audio panel chassis

Only one radio connected to audio panel then headset

Peter
Click to expand...

Audio shields should only be connected to a single ground at the audio panel.
 
petersb said:
White noise volume is lower at low RPM, it is not alternator whine.
When engine not running white noise is present for only two seconds after PTT pressed.

Peter
Click to expand...

I would follow up with a few tests here.
With engine on, alternator off, what happens? (regulator issue?)
Engine off, no noise, turn on a battery charger and bump buss voltage back up to 13 volts or more. What happens? I wonder if the noise only appears with buss voltages over 12.6. If so you may have a problem in the SL40. Keep the audio panel off, in fail safe mode, so as not to confuse the issue.
 
Walt said:
Ignore the manual in this case :eek:
Click to expand...

Will do.

While I have got your attention Walt ; re dynamic prop balancing, I have reduced the vibration to .006 IPS. I did runs from 2200 to 2400 and it stayed at .006, however at take off rpm it still feels very rough.

Peter
 
petersb said:
Will do.

While I have got your attention Walt ; re dynamic prop balancing, I have reduced the vibration to .006 IPS. I did runs from 2200 to 2400 and it stayed at .006, however at take off rpm it still feels very rough.

Peter
Click to expand...

Then it likely has nothing to do with the balance, start looking for other things that can cause a rough running engine like plugs/ignition and fuel.
 
What is the SL-40 Transmit mic setting?
Mic 1, Mic 2, or Mic 1 & Mic 2?

Do you have anything else connected to the audio panel?

As Walt said, check grounds and antenna system.
 
PaigeHoffart said:
What is the SL-40 Transmit mic setting?
Mic 1, Mic 2, or Mic 1 & Mic 2?

Do you have anything else connected to the audio panel?

As Walt said, check grounds and antenna system.
Click to expand...

Nothing else connected to audio panel.

Reduced following settings on SL40 to half default settings:

Receiver squelch
Mic Level
Mic Squelch
Sidetone

Antenna shield is grounded
Shielded cable to jacks is grounded at one end

Peter
 
petersb said:
Nothing else connected to audio panel.

Reduced following settings on SL40 to half default settings:

Receiver squelch
Mic Level
Mic Squelch
Sidetone

Antenna shield is grounded
Shielded cable to jacks is grounded at one end

Peter
Click to expand...
Look at the bottom of page 13 in the install manual. Make sure it is only set to mic 1, not mic 1 & mic 2.
 
PaigeHoffart said:
Look at the bottom of page 13 in the install manual. Make sure it is only set to mic 1, not mic 1 & mic 2.
Click to expand...

It is set for Mic1& Mic2. I assume this is to allow either seat to be able to transmits if their PTT is pressed.

During my testing their has only been one headset installed at a time.

I don't see any warning about having it set this way, what us the issue with this setting ?

Regards Peter
 
Hello Peter,
I've recieved some feedback from some of our RF engineers on this issue and basically we'll need a little more data concerning the issue #2 of your writeup. in this case what frequency the SL is transmitting on and what AM broadcast frequency you beleive you're hearing in the audio, if it is AM broadcast then it?s probably something between 550 KC to 1610KC but you may also be hearing an FM broadcast station. Is there anyway possible for you to be able to discern this and tell us what frequency the station is on?

Best Regards,
 
petersb said:
It is set for Mic1& Mic2. I assume this is to allow either seat to be able to transmits if their PTT is pressed.

During my testing their has only been one headset installed at a time.

I don't see any warning about having it set this way, what us the issue with this setting ?

Regards Peter
Click to expand...

You know what they say about assumptions...

When you wire a radio through an audio panel, you only need to connect one mic input (#1). My guess is that the #2 microphone input is connected to some unterminated wire which is acting as an antenna, picking up some of your own RF, and RF from nearby AM stations.

If it's not that, it is probably an RF issue like Walt and I said before. Find someone qualified to look at it.

I'm done.

Paige
 
TrekLawler said:
Hello Peter,
I've recieved some feedback from some of our RF engineers on this issue and basically we'll need a little more data concerning the issue #2 of your writeup. in this case what frequency the SL is transmitting on and what AM broadcast frequency you beleive you're hearing in the audio, if it is AM broadcast then it?s probably something between 550 KC to 1610KC but you may also be hearing an FM broadcast station. Is there anyway possible for you to be able to discern this and tell us what frequency the station is on?

Best Regards,
Click to expand...

Trek

Was listening to 610 am and 1010 am, it was also on FM can't recall the frequency.

This is only an issue when in my hanger, the radio is within 20 feet. Not an issue when outside the hanger. I only mentioned it in case it had something to do with issue #1, white noise.

The white noise seems less now, the last change was to program only Mic1 as suggested by a previous message, does this mean the copilot cannot transmit , not sure if this change had any affect.
 
PaigeHoffart said:
You know what they say about assumptions...

When you wire a radio through an audio panel, you only need to connect one mic input (#1). My guess is that the #2 microphone input is connected to some unterminated wire which is acting as an antenna, picking up some of your own RF, and RF from nearby AM stations.

If it's not that, it is probably an RF issue like Walt and I said before. Find someone qualified to look at it.

I'm done.

Paige
Click to expand...

Paige

Just before you are done, what do you mean only one Mic is wired to the Audio Panel ?

Where is the copilot mic wired ?

The 240 installation manual shows both Mic's and headphones wired to the 240
then single connections to the SL40

Best Regards Peter
 
petersb said:
Paige

Just before you are done, what do you mean only one Mic is wired to the Audio Panel ?

Where is the copilot mic wired ?

The 240 installation manual shows both Mic's and headphones wired to the 240
then single connections to the SL40

Best Regards Peter
Click to expand...

OPPPP's , sorry Paige, I was thinking backward there for a minute.

You where talking about the 2nd Mic for the SL40, which of course is not needed due to the 240

Peter
 
petersb said:
Paige

Just before you are done, what do you mean only one Mic is wired to the Audio Panel ?

Where is the copilot mic wired ?

The 240 installation manual shows both Mic's and headphones wired to the 240
then single connections to the SL40

Best Regards Peter
Click to expand...

He meant what you said. Both mikes to the 240; one mike output to #1 mike input on the SL40. So set the SL40 to "mike 1 only". The 240 will switch which mike is sent to the SL40. Does the SL40 mike#2 have anything connected to it? It shouldn't.
 
BobTurner said:
He meant what you said. Both mikes to the 240; one mike output to #1 mike input on the SL40. So set the SL40 to "mike 1 only". The 240 will switch which mike is sent to the SL40. Does the SL40 mike#2 have anything connected to it? It shouldn't.
Click to expand...

Bob

Yes, I was sitting in my car with a few minutes to spare and responded to Paige a little too quick. No I don't have anything connected to the SL 4O Mic2, however I did disable it in programming and I think that may have improved things

Thanks for responding. Well I guess I've had my two Penny's worth on this topic

Peter
 
white noise solved SL-30

appreciate this post. I was also having white noise from headset #2. From the SL-30 system menu I selected only mic 1 instead of mic 1 & 2 setting. that solved my white noise problem.

update1: I also added the Oregon mic muff as recommended by others. I like them.
 
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