[amsat-bb] Intermittent loss of full-duplex with Arrow, built-in-duplexer and TH-D72a

[John Brier]

I may have found the cause of the distortion, and another bit of helpful info:

I got a copy of the audio of the pass from someone else and I'm
comparing it to mine. When I am transmitting there are at least three
places where I can hear other transmissions, clearly different FM
transmissions of other people talking. At one point I even hear a
roger beep like sound followed by another voice. That could just be a
symptom of whatever is causing the desense though.

Regarding this:

On Fri, Aug 19, 2016 at 2:12 PM, James Duffey <jamesduffey at comcast.net> wrote:
> If I had to guess, I would say that you have a feed line problem, either a short or open.
>
> Another option may be a poor connection or a short in the diplexer. - Duffey KK6MC
>

I have suspected the duplexer myself. There is only one connection
from it to the radio. No adapters. The feedline from the duplexer has
an SMA connector and screws right onto the SMA on the Kenwood TH-D72a.
Still it could be the BNC connectors that go to the antenna.

I asked the owner of Arrow antenna about the possibility of this issue
being caused by the duplexer and he was not aware of that ever
happening before.

:-/


On Fri, Aug 19, 2016 at 2:12 PM, James Duffey <jamesduffey at comcast.net> wrote:
> If I had to guess, I would say that you have a feed line problem, either a short or open.
>
> Another option may be a poor connection or a short in the diplexer. - Duffey KK6MC
>
> On Aug 19, 2016, at 11:48 AM, John Brier <johnbrier at gmail.com> wrote:
>
>> For the third time I've lost the ability to hear myself on the
>> downlink of SO-50 using this setup. This was on today's 1521 UTC SO-50
>> pass.
>>
>> In the past I had what appeared to be very similar behavior with a
>> different arrow antenna, no duplexer and two radios. I troubleshot
>> that issue to the screw in the gamma match coming lose which caused
>> high SWR.
>>
>> In this case I tested the SWR with my MFJ-259B SWR analyzer and it was
>> 1.1:1 and X=45-55 across almost the entire band.
>>
>> I actually was able to hear myself in the beginning of the pass and
>> then it got worse until the point where I could not hear myself for
>> the rest of the pass.
>>
>> Actually, in this case, unlike the other two times where I wasn't able
>> to hear myself on the downlink I had another unusual behavior which
>> was I *WAS* able to hear myself but it was extremely loud and
>> distorted. This happened maybe twice in the middle of the pass and
>> then after that I just couldn't hear myself when I transmitted.
>>
>> When I was able to hear myself very loud and distorted I felt it
>> wasn't how I was getting into the bird, but somehow my radio was
>> demodulating my 2 meter transmission. I confirmed with W4FS who was
>> also on this pass that my audio never sounded odd.
>>
>> Very annoying and my only guess as to what could be causing this is
>> some sort of external interference occasionally getting into my radio.
>>
>> Any ideas?
>>
>> 73, John Brier KG4AKV
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