[Elecraft] K2 - Resonate noise on audio

[Phil Wheeler]

I'd check the KSB2. How well are the xtals 
grounded (solder joints and such)? Were any 
problems introduced while installing the crystals? 
etc. KSB2 is a pretty compact board so easy to 
introduce solder bridges and such.

If you did mods to the K2 before adding the KPA100 
did you use it QRP in that period?

73, Phil w7ox (K2 #380 with KPA100 and KAT100)

On 3/19/14, 10:01 AM, Jason V wrote:
> 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