[Elecraft] K2 - Resonate noise on audio

[Jason V]

I did a lot of testing to try and resolve and isolate the issue.  So here are
all the details and sorry in advance for being so verbose.  Also very green
to amateur radio. Got my ticket this year in January and the ink isn't even
dry.   So please bear with me.

I purchased a QRP K2 (s/n: 00026, not a typo) second hand and was fairly
happy with it after performing an alignment and setting the filters.  I
opted to build and install the KPA100 and KAT100 requiring numerous upgrades
to support.  Firmware upgrade, VFO, BFO, KPA/KAT100 mods provided with the
kits, and replaced the filters with a matched set.  I have doubled checked
board level mods on the K2 n+1 times and they are done per the manuals.

when doing an alignment and setting the filters after completion there is
resonate noise outside the skirts of the filters which wasn't there before. 
It is present on all bands and modes with the same interval.  Stripped the
radio back down to a QRP rig and it is still present.  Attached a dummy load
and tuned to the 7Mhz birdie.  When ever the birdie was within the filter
the resonance would be present, outside it goes away. 
Links to screen shots.
No birdie on cw filter. http://goo.gl/qvMGOq
birdie @ ~633 Hz. http://goo.gl/irDakg
birdie @ ~721 Hz. http://goo.gl/lBEacm

So I brought the Radio to work and put it on the IFR 1900 and it Tx's and
Rx's just fine.   Probed each of the new crystals and they all appeared fine
as well, steep skirts, consistent width, and no spurs.  I have screen shots
of the IFR if needed.

Comfortable it wasn't going to splatter the bands I put it on the air last
night.  Logged quite a few DX QSOs via JT65 and listened in on some SSB
which sounded great.  So the good news is the problem doesn't exist within
the filtered audio.  But it bugs the bejesus out of me knowing it wasn't
there before the mods.

The only options installed during the time of test were the RX160, KAF2,
K2NB2, & KSB2. Neither of which have been modified in any way.  Except for
the new crystals on the KSB2.

Any help or guidance would be greatly appreciated! 

Best Regards,
Jason - KV4TY




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