[TenTec] 253 Keying Loop - Intermittent

[Rick Williams]

My problem was mechanical and would occur at 10 watts drive.  Suddenly my PTT would not function.  It was the same in CW or SSB.

Hence my thought of a bad RCA connector or faulty relay contacts.  The former, more likely, looks like it was the culprit. 

If the PTT worked I haven't had a problem when running power.  I do agree that K6 is pretty close to some traces.

73,
Rick
VE7TK



 
     Subject:   Re: [TenTec] 253 Keying Loop - Intermittent     From:   Ken Brown     
 
     Date:   Sat, 01 Sep 2007 14:27:22 -1000    
 
           
Hi Rick,

K6, the relay that interrupts the keying loop (the exciter in / exciter 
out path) in the 253 is located on the the same PCB as the KW (SWR) 
Bridge. In my opinion the keying loop traces are way too close to the 
high power RF paths on that board. When I had my keying loop running 
through my 253 I had some difficulties too. Removing the 253 from the 
loop made the keying problems go away, but then the 253 no longer has 
the ability to prevent keying when it detects a high SWR or other fault 
condition. I thought about trying to make some kind of a shield out of 
copper sheet or PCB material, and installing it between K6, R7 and rest 
of the components on that board. I have not tried it yet.

My guess that RF pick up by the keying loop as it passes through the 
81486 board is causing the problem does not seem to be supported by the 
fact that you could make the problem go way by wiggling the cables or 
resoldering connections. Still I think it would be better if there were 
some shielding between the RF and keying loop on that board.

N6KB

 


       
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