[Elecraft] RE: new rev B K2 build: low sensitivity

[Bob - AG5Q]

Hi Andy,

I haven't had a chance to study all your data but the first numbers indicate
your signal into the mixer is going to be too large when the preamp is on.
The max input to the mixer is speced at 0.25V.  You are close to that with
0.14V and the preamp turned off.  Since the problem is apparent when the
preamp is off, it's probably better to just leave the preamp off for now to
reduce the amount of circuitry involved.

If you want to test with the preamp turned on later, reduce the input to
around 0.04 V, since the preamp has a gain of 5X.   (The high input level
could account for the overload symptom.)

Really bad operational problems can often be found by checking the DC
voltages. A bad connection somewhere will usually show up as a abnormal DC
bias condition.  Double check all the voltages around Q21 and Q22.

Also check the frequency compensation of your scope probe and be sure to use
a very short ground lead clipped right at the probe tip if possible.

73/ Bob - AG5Q