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  #1  
Old 02-15-2020, 08:06 PM
echostar7 echostar7 is online now
 
Join Date: Aug 2019
Location: Savannah
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Default FL760 , transmissions are 1/5

I flew today and I was told that I was broken and barely readable on the radio but I could receive very clearly. I tried two different headsets and there was no change in my transmissions clarity. What can be the cause? Only new thing I can think of is I added the GDL-82, can that interfere somehow with the com, or just a coincidence?
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  #2  
Old 02-16-2020, 09:44 AM
philb philb is offline
 
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It could be those stratospheric gremlins...😳

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  #3  
Old 02-16-2020, 09:57 AM
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N804RV N804RV is offline
 
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The fact that you can receive just fine. But, transmit is "1/5", makes me think its more than likely VSWR problem. When was the last time that radio transmitted good? And, did it ever work ok after you installed the GDL 82?

The GDL 82 has nothing to do with your com radio. But, is it possible you disconnected the coax from the com antenna and forgot to hook it up? Or, maybe the coax connecter was damaged while installing the GDL 82?
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Last edited by N804RV : 02-16-2020 at 10:01 AM.
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  #4  
Old 02-16-2020, 02:38 PM
echostar7 echostar7 is online now
 
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I asked for a radio check today and it was loud and clear to whoever responded at the field. It may be a different story though for artcc miles away, I'll inspect the coax connections for damage, thanks.
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  #5  
Old 02-16-2020, 03:25 PM
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N804RV N804RV is offline
 
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Quote:
Originally Posted by echostar7 View Post
I asked for a radio check today and it was loud and clear to whoever responded at the field. It may be a different story though for artcc miles away, I'll inspect the coax connections for damage, thanks.
Another thing too: on some radios its easy to get the box a little off when reinstalling it in the rack. Especially if you're not very familiar with how the latching mechanism works.

If you had your com radio out during the GDL-82 install, you might just try re-racking it to make sure it is properly seated.
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  #6  
Old 02-16-2020, 04:15 PM
BobTurner BobTurner is offline
 
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Agree with Ken. On receive, nearly anything (coat hangar) works for an antenna. Transmit is a lot fussier. Specifically, look for good connections where the coax shield is attached to the connector, and where the connector attaches to ground. Both at the transmitter but especially at the antenna end. May be something as simple as corrosion between the connector and ground.
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  #7  
Old 02-17-2020, 08:10 PM
Cumulo Cumulo is offline
 
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Being well versed in the reciprocity rules of radio communication, I am puzzled by the differentiation being applied to transmitting and receiving here. Transmitter protection circuitry kicking in?

I offer that in military comm, the RX and Tx are often not in the same place. I wonder if the FAA might sometimes have similar non co-located facilities for their Rx, TX. That could explain the anomaly. Just a guess.

I did make an aircraft VHF transmitter half a century ago from 2n708 computer transistors and it sounded pretty good with even the proverbial coat hanger attached. Crummy VSWR alone should not effect audio quality other than lower the effective output. Normally one SHOULD expect a little more solid link TO the airplane because the ground station has an edge in power output.
Ron
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  #8  
Old 02-17-2020, 08:29 PM
Jonathan Alvord Jonathan Alvord is offline
 
Join Date: Feb 2018
Location: Prosser, WA
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Quote:
Originally Posted by echostar7 View Post
I flew today and I was told that I was broken and barely readable on the radio but I could receive very clearly. I tried two different headsets and there was no change in my transmissions clarity. What can be the cause? Only new thing I can think of is I added the GDL-82, can that interfere somehow with the com, or just a coincidence?
What was the weather like that day. We lost all our coms after flying around/through a storm cell. Once the weather got better and everything dried out the comms have worked great. Several people mentions it was likely static build up. When I returned home we checked/rebedded all the antennas.
Jon
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  #9  
Old 02-17-2020, 09:38 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Cumulo View Post
Crummy VSWR alone should not effect audio quality other than lower the effective output.
Ron
Crummy SWR doesn’t just mean less power to the antenna. It also means significant power flowing back into the transmitter, where it creates all sorts of trouble.
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  #10  
Old 02-18-2020, 01:59 AM
Cumulo Cumulo is offline
 
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Quote:
Originally Posted by BobTurner View Post
Crummy SWR doesn’t just mean less power to the antenna. It also means significant power flowing back into the transmitter, where it creates all sorts of trouble.
As a guy who has designed a lot of circuitry, waded around in waveguides, magetrons and other esoteric hardware for a long time, I think I've got the subject down pretty well. It has been my experience that vswr is rarely related to "bad transmitter audio", could be, of course. But it would be a rare instance.

A more likely cause, and one I ran into often, was off frequency receivers and/or transmitters. Channels are very tight now-a-days. A particularly vexing combination to troubleshoot is a tx leaning one way and the rx the other way. Both stations work ok except the combination, and often only in one direction because one unit is more bandwidth tolerant. This result is consistent with the OP's description.

To the OP: If this get to be more than that single instance, I would check the transmitter frequency. All later aircraft radios use synthesizers. So, freq tolerance checks are simpler. Checking one freq checks them all.
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