[Elecraft] KX1 Please need help with T/R thump

[Don Wilhelm]

  Jerry,

Yes, I would look at Q7 and its associated resistor R28.  That 
transistor should saturate and prevent Transmit RF from coming into the 
receiver.  It sounds like it is not working right and the receiver 
saturates during transmit and takes too long to recover.

What you have done by increasing the value of C9 would cover up that 
receiver recovery period.
The easiest way to check Q7 is to replace it, but make certain that Q7 
base goes to at least 0.6 volts during transmit - if it does not, then 
look to R28 and the 6T-2 voltage supply to it, which should be about 6 
volts during transmit and zero during receive.

73,
Don W3FPR

On 5/24/2011 9:55 PM, Jerry W7ANM wrote:
> Thanks for your thoughts Don.
>
> I checked the STL and It's been at 2. The thump does not really change much
> on any setting of the STL. I also checked the components you suggested and
> Q2 and Q3 are installed correctly and in fact are J309s. R29 is also 22k and
> in the right place. Other associated components are correctly installed.
>
> Rick KL7CW suggested an experiment for me to try. That was to connect a .02
> to .1 cap across C9 to see if it made a difference. At first I tried a .1
> and the thump was completely eliminated and changeover dead quiet but it
> made the T-R delay about a second long. (with Menu T-R set to 0). I next
> tried a .047 and that seemed to do the trick. I could still hear a very
> slight quiet "poof" at changeover and the T-R delay is slightly longer than
> before with the thump but still very acceptable. About the equivalent of
> setting the Menu T-R delay to 30 or 40. Definitely QSK not as fast as my K2
> but I'm not sure the KX1 was ever supposed to be fast as the K2.
>
> Still something not quite right? In theory the parallel cap shouldn't be
> needed but at this point maybe it's a case of component tolerance/anomalies?
> Any other ideas?
>
> Thanks for all your help and suggestions.
>
> 73,
> Jerry
>
>
>
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