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PH-SCP

Well Known Member
Hi Guys,

Because of European laws, we must now all install VHF-radio's with 8.33 KHz channel spacing so I managed to buy a used Garmin GTR225 radio and also purchased a GMA-240 audio panel. The idea was to use the GTR225 as COM1 and my existing SL30 as COM2.

Installed an extra VHF antenna and built a new wiring loom.

It seems to work relatively fine except for two things;

1) I cannot transmit from the pilot position. Most likely I misplaced one of the pins in one of the connectors. Can be cured fairly easily I guess;

2) When transmitting from the co-pilots position I hear a rather strong background whistle. Doesn't make any difference whether using COM1 (the GTR225) or COM2 (the SL30). Playing with volume and squelch doesn't cure it and yes, I am not listening out on the other radio on the same frequency nor do I have a speaker that could play a roll. Any ideas how to get rid of this annoying whistle ??

Thanks in advance.
 
I have no idea, but suggest you fix problem #1 first. After that there's a chance problem #2 will be gone.
 
PH-SCP said:
Hi Guys,

Because of European laws, we must now all install VHF-radio's with 8.33 KHz channel spacing so I managed to buy a used Garmin GTR225 radio and also purchased a GMA-240 audio panel. The idea was to use the GTR225 as COM1 and my existing SL30 as COM2.

Installed an extra VHF antenna and built a new wiring loom.

It seems to work relatively fine except for two things;

1) I cannot transmit from the pilot position. Most likely I misplaced one of the pins in one of the connectors. Can be cured fairly easily I guess;

2) When transmitting from the co-pilots position I hear a rather strong background whistle. Doesn't make any difference whether using COM1 (the GTR225) or COM2 (the SL30). Playing with volume and squelch doesn't cure it and yes, I am not listening out on the other radio on the same frequency nor do I have a speaker that could play a roll. Any ideas how to get rid of this annoying whistle ??

Thanks in advance.
Click to expand...

Hello Simon,

We agree that fixing the Pilot PTT should be easy. The button on the stick only needs to ground pin 34 on connector J2401 and the selected COM radio should transmit.

For the noise issue, this might be the result of not isolating the headset jacks (but could be lots of things like ground loops). If you have a metal panel, please be sure that insulating shoulder washers are used around the jacks.

Once you get the pilot PTT problem fixed, you might try turning off the GMA 240 which drops the bypass relay and allows you to use the COM1 radio directly to see if the whistle is still present.

Thanks,
Steve
 
Hi,

Today I opened up my harness and found that pin 34 on connector J2401 was misplaced. Corrected that and re-installed. Transmitting from the left seat works fine now, thanks again for the input !

I plugged in both headsets which took care of the whistle. Everything works great except switching off the GMA240 and transmitting directly through COM1, that doesn't work in my situation. Any advise here ?

Love this forum, your answers really helped 👍👍
 
PH-SCP said:
Hi,

Today I opened up my harness and found that pin 34 on connector J2401 was misplaced. Corrected that and re-installed. Transmitting from the left seat works fine now, thanks again for the input !

I plugged in both headsets which took care of the whistle. Everything works great except switching off the GMA240 and transmitting directly through COM1, that doesn't work in my situation. Any advise here ?

Love this forum, your answers really helped 👍👍
Click to expand...

Sure you used the pilot's (left seat) headset?
Did your radio show a T or similar, indicating it was trying to transmit? Or could you still hear the receiver even with the PTT pushed?
 
BobTurner said:
Sure you used the pilot's (left seat) headset?
Did your radio show a T or similar, indicating it was trying to transmit? Or could you still hear the receiver even with the PTT pushed?
Click to expand...

Hi Bob,

I tried switching off the GMA-240 and just listen to the GNC225A. I can very faintly hear ATC in the back with the engine off. I am sure I won't be able to hear anything with the engine running.

Another problem occurs with my music-2 input into the GMA240.
Worked fine with my previous intercom (PM3000 TYPE 119311 INTERCOM).
Connecting the same wires into the GMA240 produces a very strange sound as if half the orchestra went home early. Could this be some sort of ground loop problem ? Any cues would be appreciated.

Simon
 
This is so simple I hesitate to ask, but did you turn up the receiver's volume?
Are you using stereo headsets? If so, you should only hear the radio in one ear with the audio panel off. If you are using mono headsets, make sure you have not reversed the left and right wires from the intercom to the jack. If wired for mono make sure you have used the correct (I think it is the right) channel. (If the jack is wired for stereo but you have mono headsets, here's a quick check: pull the headset plug out about 5 mm. Can you hear the radio now?)

As to the music, ground loop problems usually do not show up with the engine off. I'd start by confirming that the left, right, and ground wires from the music to the intercom are all properly connected.
 
Hi Bob,

Yes turned up the volume and could hear ATC very faintly in the background. I have DC ANR headsets and will try pulling the plug by 5mm or so and hear what happens.

Music problem is cured. Ground wire was improperly connected and this works great now !

Thanks for all the feedback. :) :)
 
I hesitate to tell you this but eventually your SL30 will be outlawed. 25KHz spacing is not compatible with areas designated 8.33KHz. Although some of the frequencies have the same apparent designation, they are, in fact, different.
 
paul330 said:
I hesitate to tell you this but eventually your SL30 will be outlawed. 25KHz spacing is not compatible with areas designated 8.33KHz. Although some of the frequencies have the same apparent designation, they are, in fact, different.
Click to expand...

Yes Paul. that is exactly the reason for installing a GNC225A which is an 8,33 radio. I am using the SL30 as a second radio to listen to ATIS and keep a listening watch on emergency frequencies.
 
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