Dulles Repeater Fixed

Frank Gentges metavox at earthlink.net
Wed Jun 16 15:11:11 CDT 2010

We have had several repeater problems. They have been fixed and the 
repeater is back on the air.

We were chasing down several problems, none of which were discussed on 
the Internet.  I had to find each solution on my own even though the GE 
Mastr II is well covered. Craig Brown, Allon Stern, Rick Miller and Mike 
Nowlen all helped with suggestions and encouragement.

In short....

1.  Receiver sensitivity was down at 1.6 microvolts and shold be more 
like 0.3 microvolts.  After much effort we tried adding a 5 picofarad 
capacitor across an 18 picofarad capacitor.  That silly little 5 
picofarads changed the sensitivity to 0.23 microvolts.  That should give 
us better range.  Let us know if you are able to get into the repeater 
from sites you could not do before.

2.  We all were finding times when the repeater went into a mode where 
it had really bad buzz at 60 hz., transmitted ID but did not respond to 
input signals.  We were puzzled by this problem that came and went. 
Finally, Allon Stern suggested we look into the power supply.  After 
some thought, it seemed possible that one of the three big filter 
capacitors was intermittently going open circuit and putting raw 
rectified DC on the power amplifier.  We placed three external caps we 
had tested across the existing ones.  This saved us the work of carrying 
the power supply down in another trip to the building.  Time will tell 
if this is a fix.

3.  The tone coded squelch being transmitted was way down from where it 
should be.  After some signal tracing we found a missing connection.  We 
do not know why but added a jumper wire and it fixed the problem.

I will be at Saturday's meeting and will give a summary of the problems 
and try to answer questions.

The repeater is now returned to amateur service and encourage everyone 
to once again use it.  The repeater is on 145.31 with CTCSS tones of 77 
Hz in and out.  We have programmed the repeater to not transmit the 
tones when it is doing normally timed identification on CW and voice. 
This will let you put a radio in the shack and only hear the repeater 
when someone is using it.

I feel bad it has taken so long as life and Hamvention went on and I 
want everyone to get back into the habit of meeting on the repeater.

Frank K0BRA

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