I was wondering if anyone know what causes one radio transmission to bleed into another radio that is on a different frequency?* If both of my COM are selected on the intercom and when I transmit on one frequency, it bleeds into the other radio which is on a different frequency with harsh noise.
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Noise from one radio to another
- Thread starter Bavafa
- Start date
The radios are 650XI and GTR20 and the audio is GMA 245 (all Garmin)
The antennas are Comant whip.
Edit:
Looks like there is a DIP switch #3 on the GMA 245 that mute the monitored COM. I will pull the GMA to see what is the position of this DIP switch and if it is OFF, I will turn it to ON and test.
The antennas are Comant whip.
Edit:
Looks like there is a DIP switch #3 on the GMA 245 that mute the monitored COM. I will pull the GMA to see what is the position of this DIP switch and if it is OFF, I will turn it to ON and test.
Last edited:
For what it is worth I see the same - almost. I have the gtn650 as com1 and gtr20 as com2 with a 345 panel. Transmit on 650 is heard on gtr20 receive. Transmit on gtr20 is not heard on the 650 receive. The interference occurs when different frequencies are selected. I probably want to flip that dip switch too but I had chalked it up to the gtr20 having a little different circuit design or less internal circuit shielding.
Carl Froehlich
Well Known Member
This problem with the GTR-200/20 has been previously reported. I’ve ferried a RV-14 with that radio on Guard and had the same problem - making it useless for monitoring (Comm #1 was a GTN-650). I’d need to have test stand data to verify but I’d guess that the radio’s receiver front end selectivity is not that great. I don’t have this radio in any of my builds so I have just this one data point.
The bandaid is to make the wire connection between the 650 and the GTR-200 (or GTR-20) that desensitizes the GTR receiver when transmitting on the GTN-650.
This does however eliminate the option of split comms (pilot communicating on one radio and the copilot on the other radio on a different frequency). Perhaps few builders consider this an issue.
Mehrdad - is this connection made on your install? If so, then there are other potential causes of your problem to chase down.
Carl
The bandaid is to make the wire connection between the 650 and the GTR-200 (or GTR-20) that desensitizes the GTR receiver when transmitting on the GTN-650.
This does however eliminate the option of split comms (pilot communicating on one radio and the copilot on the other radio on a different frequency). Perhaps few builders consider this an issue.
Mehrdad - is this connection made on your install? If so, then there are other potential causes of your problem to chase down.
Carl
Carl,
If you are referring to the Transmit interlock (Pin 5 of GTR20 to Pin 11 on P1003 of GTN650) then yes, I do have that wire.
Carl Froehlich
Well Known Member
Mehrdad,
Ok - the jumper from the 650 to the GTR-20 is installed. Now you are left with the usual suspects.
I assume you have the comm antennas mounted in the normal places on your RV-14. Is this correct?
Have you ever put an antenna analyzer on the comm antennas? This will ring out any connection type issue.
The quick thing to do is to swap the comm antennas between the 650 and the GTR-20 and note any changes.
Carl
Ok - the jumper from the 650 to the GTR-20 is installed. Now you are left with the usual suspects.
I assume you have the comm antennas mounted in the normal places on your RV-14. Is this correct?
Have you ever put an antenna analyzer on the comm antennas? This will ring out any connection type issue.
The quick thing to do is to swap the comm antennas between the 650 and the GTR-20 and note any changes.
Carl
Carl,
You are correct, my antenna are in the standard location for the RV14, at the belly.
I have not used the antenna analyzer as I don't have access to one. I am hoping flipping the DIP switch 3 to ON position will fix this issue. Swapping the Coax of both antennas is not going to be easy as my remote radio is far away from the 650.
You are correct, my antenna are in the standard location for the RV14, at the belly.
I have not used the antenna analyzer as I don't have access to one. I am hoping flipping the DIP switch 3 to ON position will fix this issue. Swapping the Coax of both antennas is not going to be easy as my remote radio is far away from the 650.
UnPossible
Well Known Member
I was having this same issue with my RV-10. I pulled the audio panel, flipped DIP switch #3 to "On" and for the last couple of flights it has seemed to solve the problem.
The second COM is still indicating RX when I transmit on the first com, but I'm not hearing the static bleed over that I was.
The second COM is still indicating RX when I transmit on the first com, but I'm not hearing the static bleed over that I was.
Think about it - you have a radio receiver capable of detecting transmissions clearly from a hundred (plus) miles away. You have it’s antenna sitting less than three feet away from another antenna attached to a radio that can transmit clearly to one hundred (plus) miles away. Sort of like shouting into the ear of a person right next to you….no wonder that it doesn’t make any difference what frequency its tuned to in the band.
Bleed over is hardly unexpected - which is why they put in transmit/receive inhibits and clever solutions in audio panels…..
Paul
Bleed over is hardly unexpected - which is why they put in transmit/receive inhibits and clever solutions in audio panels…..
Paul
Carl Froehlich
Well Known Member
Perhaps, but I do not have this problem in the 8A, the 10 or the 8, nor do I have any transmit/receive inhibits. All use the GTN-650 and the Dynon (Trig) radio as Comm #2.
Carl
Majorpayne317641
Well Known Member
I know this is almost a year old but I have one case that is the same problem in my RV-8A with a GTN355 (essentially a smaller 650 without the NAV side) and a GTR200. I have noticed it does not always interfere but it will randomly interfere and is annoying when monitoring comm 2 while transmitting on comm 1. I tried messing with the receive squelch but it didn’t help. I will try the dip switch on my 245. I didn’t think about that option. I do have the interlock wired from my 355 mic switch to the interlock in on the 200. When trying it in my hangar it worked fine. But I noticed in certain geographical areas (or maybe certain freqs I TX on from the 355) it will bleed over.
My antennas are also both on the belly and I suspect that’s why.
Desert Rat
Well Known Member
I know that the RV14 puts both those antennas side by side on the belly. Lot's of people on the other models have also done something similar.
But, Garmin installation instructions will tell you that your comm antennas should be 6' away from each other or have one on the bottom of the airplane and one on the top because of this bleedover issue. They also tell you that comm antennas should be as far away from ELT or GPS antennas as possible, so on something as small as an RV you have to pick your poison.
But, Garmin installation instructions will tell you that your comm antennas should be 6' away from each other or have one on the bottom of the airplane and one on the top because of this bleedover issue. They also tell you that comm antennas should be as far away from ELT or GPS antennas as possible, so on something as small as an RV you have to pick your poison.
Dad's RV-10
Well Known Member
I recently encountered this with a GTN 650Xi, GTR 200, GMA 240 and two belly mounted com antennas on an RV-7.
The GMA 240 doesn't have dip switches but grounding pin 30 on connector J2402 accomplishes the same thing.
I have all of the interlocks wired and the bleed through persisted.
It's really semantics but flipping dip switch #3 (or grounding pin #30 on the GMA 240) doesn't really "solve" the problem as much as it "masks" the problem. As UnPossible wrote above, you'll still see RX on the #2 com when transmitting on #1 because com #1 is still bleeding through to com #2. But since com #2 audio is now muted when transmitting on com #1, you can't hear the bleed through.
Carl Froehlich
Well Known Member
I suggest you read my post on the GTR200 receiver front end shortfall. It makes the GTR-200 a poor choice for Comm #2 if you plan on using it to monitor something like Guard when transmitting on the 650. While antenna separation is always a factor you may be challenged achieving enough separation in an RV to eliminate the issue. As you know moving an antenna to the top of the fusleage is not viable on an RV-8 or RV-8A.
Carl
+1. This was true 10 months ago, and is still true today. The signal from your nearby #2 com is over a billion times stronger than the one from a guy 50 miles away. Asking your receiver to reject an off frequency signal that is a billion times stronger is asking a lot. Yes, some receivers can do it, but in general it shouldn't be shocking that some cannot.
Majorpayne317641
Well Known Member
Has anyone thought about trying the new radio out later this month by Garmin? I have been eyeing the GNC215 as a future upgrade to add nav capabilties. Maybe it also has better filters for our set up.
Flyingleap
Well Known Member
Advanced Features : Garmin GMA350
"A split COMM mode lets the pilot and copilot broadcast on independent frequencies."
Well, the audio panel lets you do it.....but, does it really work on all radios, maybe not.
"A split COMM mode lets the pilot and copilot broadcast on independent frequencies."
Well, the audio panel lets you do it.....but, does it really work on all radios, maybe not.
