Re: New KX1 low power and 20m oscillation

Posted by Geoffrey Mackenzie-Kennedy-3 on May 08, 2012; 11:39pm
URL: http://elecraft.85.s1.nabble.com/New-KX1-low-power-and-20m-oscillation-tp7531133p7541070.html

Hello Stan,

If Q7 is not conducting and is not in effect grounding one side of CA, then
a loop is created between the input (Q1 Gate) and output stage of the
transmitter.  Part of this loop contains the Rx RF Gain pot R1, the Rx's
input tuned circuit, and the coupling between pins 1 and 6 of U6 be it
inside or external to the chip.

To eliminate (or not) the possibility that on 20m transmitter is unstable
because Q7 is not removing this loop, I suggest that while transmitting you
wind down the Rx RF Gain pot R1  to see if the spectrum improves.

I am curious as to why the sidebands on 20m are spaced at 60 Hz intervals.

73,

Geoff
LX2AO



On May 08, 2012 at 18:07 +0200, Stan Gibbs wrote:

> As I said in my original post, Q7 is the place where my DC troubleshooting
> measurements differed from specs.  The base of Q7, which is supposed to be
> 0.7V, is -0.895V on 40 and -0.195 on 20.  The voltage on Q7 should
> definitely be positive in order for it to ground capacitor CA, so
> something
> is screwy.
>
> Someone suggested that either C45 or C32 were possibly bad, allowing RF on
> to the base of Q7, which might cause the bogus voltages.  I tried adding
> additional capacitance in parallel with C45/C32, but that had no effect.

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