[Elecraft] K2 rev B low sensitivity

[Wallace, Andy]

Hi, Folks... Looks like I got unsubscribed somehow, on Sunday, and
I thought the List was down! Hope it wasn't for some transgression...
I sent a post about this K2 but it never made it through.

Anyway, to follow-up on the K2 of mine with low sensitivity: resoldering
Q22 (the post-mixer amp transistor), RFC11 (which is on its collector),
and C161 (which is the IF coupling cap out of Q22) seems to have improved
things immensely. 

Lessons learned:

1) Check EVERYTHING Gary tells you to.
2) Check 'em again!
3) Even if it looks good, it may be a cold solder joint.

In this case, I had suspected C161 and RFC11 just because they were 
bottom-mounted components which were soldered on the top of the board.
The interesting thing is that I built the kit using an excellent Metcal
soldering iron (RF heated, fancy, expensive) and in most cases, did so
while using a binocular microscope. Looking at RFC11 and C161's solder
the joints all LOOKED super, even under high magnification. But where
lab noise was S-1 with a short wire, before re-soldering, it became
S-9 afterwards. My suspicion was there might have been some sort of
contamination on the leads and the solder did not adhere well. 

Regardless, the rig IS better. Not having had a K2 before, I am still
suspicious that it is not as hot as it could be.

In comparing perceived signal strength with the K1 I have, sensitivity
seems to be even with the K2 preamp ON. The Elecraft webpage quotes the
rx sensitivity in both rigs to be 0.15 uV and that is with the K2 preamp
on. Interesting!

However, the ARRL review shows the K1 sensitivity as -129 dBm. K2
is -133 with the preamp off, and -137 with the preamp on -- so in
the case of their test transceiver, the K2 beat the K1 even with the 
preamp off. 

Another interesting point is that the S-9 measurement of the K2
in ARRL lab with preamp off is 115 uV, and preamp on it's just 19 uV.

When I was doing my signal tracing earlier, my sig gen was set to over
300 uV to get an S-9 reading! So things have improved. I have not 
rechecked this measurement, though, and will do so. It must be below
300 uV now, and if it's in the 100-125 uV range I'll call the set "fixed."

I would like to hear from anyone else on the List who can run that
measurement.
With a properly calibrated (by the manual) S meter, what is your input level
for S-9 signal with preamp on and off? Thanks... 

The K2 seems wonderful so far and I just want to make sure mine isn't still
partly deaf, and want to find the problem if there still is one.

While still deaf, however, my first QSO was with a fellow in NC. Not DX,
but hey, mojo -- he was using a K2 also! My second QSO was with Tom Hammond,
N0SS -- get well soon, Tom. 

-Andy

PS I hope people don't mind my generally long-winded postings...