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[TowerTalk] Signal losses in reception-Summary/TNX

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Subject: [TowerTalk] Signal losses in reception-Summary/TNX
From: (Jose de Sa) (Jose de Sa)
Date: Tue, 17 Feb 98 00:04:50 CET
Thank you very much for all the replies concerning my question,
I did clean up the T/R Relay contacts and it seems it has improved
a bit.
Due to several requests Iam posting all replies I got concerning
this matter, Hope this helps.
73 and good DXing,
                   Jose de Sa  CT1EEB

----------------------------cut here-----------------------

Hi Jose
Regarding the technical question on your Ameritron AL-1500 AMP. The
loss is probably due to the antenna switching circuit. I think your
amp uses pin switching diodes in that circuit. It sounds like more
loss than normal. I would check the diodes and related circuit.

73's and cu in the pile up


The first thing that I would check is the contacts of the chageover relay
on receive--the normally closed side(s)--to be sure they are very clean.
The TX contacts may be less susceptible to losses when not clean, but the
receive side may add some resistance to the line.  You might also check
the receive bridging wire to be sure the solder joints at the contacts are
very good--retouch with a soldering iron.  These would be my first points
of suspicion.



What is the SWR between the xcvr and the amp when the amp is in line?
Check the SWR 
1. while exciting the amp, 
2. and when the amp is in standby, 
3. and when the amp is removed completely out of the circuit.


Go directly to the TR relay.  Ameritron uses an external relay not a
vacuum relay and see if the contacts are corroded.  You could use a relay
contact burnishing tool to clean them.  Or some good quality paper. Do
not use a file.   If this doesnt clear them up then I suspect the coax.
Its a direct run from the input to the relay to the output SO239s.  That
is the only two things in the path when the Amp is not transmitting.

Should be easy to debug and fix.  Replace coax if it seems bad.  Use high
quality Teflon coax.  RG 142 if possible.   But I bet your relay has
arced and built up carbon.  The problem probably was caused by hot
switching.....does it throw a spark when you use it in CW on the first
dit?  If so the relay is too slow.  You could upgrade the amp by putting
a fast vacuum relay in place of the open frame relay.  Much faster and
quiter.  I hate that amp for that very reason.  That spark it throws can
be heard in all radios in a multi multi.
Jay, WX0B

Jose, there are several things I would check.

1. I would replace the coax between the transceiver and amplifier.

2. Ordinarily, I would say the relay in the amp is dirty and needs to be
cleaned or replaced.
At times, the response before pull in can create tiny arcs every time
you key the transceiver.

3. Not that familar with the Ameritran, but if it has any sort of low
pass filter built into the
input circuit, I would replace it.



Use the 870's auto tuner to tune the coax between the transceiver and amp
and I bet your loss goes away.
Good luck

I would clean the contacts on the relay in the Amp. gl es 73 Art

Hi Jose. If it's posseible, you might check the contacts on the T/R 
relay. I have had problems like that before and it was dirty contacts on 
the relay. 73

i have seen that with other amps.  check the rx contacts
 on the amp relay.  since you rarely transmit through them
they tend to build up oxides and just plain dirt.  try 
cleaning the contacts and see if that helps.

Buenos Dias, Jose de Sa:

        My Ameritron AL-811H had a T/R relay that was not enclosed. A tiny 
of dust got between the contacts and caused a loss of receiver sensitivity.
I pulled a small piece of paper between the contacts (like we used to clean
a Vibroplex bug) and solved the problem.

GL! 73 Gene K7dBV                       <>

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