[Elecraft] [K2] Post-Mixer signal levels

[Brian Handy]

Following up on my own note - the receiver basically works, I can hear the input 
signal coming through the headphones.  When I turn off the input 7MHz signal, 
the Q22 collector goes up a bit to 6.56V.  It's not a big jump from where it 
was, but it is consistent and steady.

Thanks

Brian AE7JW




----- Original Message ----
From: Brian Handy <holy_tire_iron at yahoo.com>
To: elecraft at mailman.qth.net
Sent: Sat, January 22, 2011 10:37:29 PM
Subject: [K2] Post-Mixer signal levels

Hi all,
elecraft at mailman.qth.net
I'm in the middle of my K2 build and have posted here before about a separate 
transmitter issue.  I decided to go back and check my receiver front to back to 
see if I found anything, and it seems I have something ... not sure what it is 
though.

With a 0.14V signal coming in, RF gain all the way down, preamp+attenuator 
turned off ... I find a few things that are a bit curious.

The signals on both sides of D6 are 0.11V (the DC levels are fine).  Seems I 
should see a little bit different signals on both sides of that diode, and I'm 
not.  Following through the circuit per the signal tracing section:~

R72 - 0.128V (should be 0.077)
R73 - 0.128 (0.077)
R80 - 0.236 (should be 0.079)
Q22 Collector - 6.43V!  (Should be 2.2V).

Lacking any other information, it seems the signal coming in is just a bit hot, 
and this is propagated through Q22.  OR, I have something oscillating here.  The 

frequency counter sees about 11.9Mhz on Q22 (signal generator is 7MHz).  


This section of the circuit isn't all that complicated, but I'm not seeing what 
the deal is.  Any advice?

Cheers

Brian AE7JW