[Elecraft] K2 U10a on control board oscillates on receive

[Marshall Jose]

Followup: After receiving a wonderful and long list of suggestions from 
Gary, I understood that the U10a oscillation on receive is not a 
pathological matter and that I shouldn't worry about it.

And, embarrassingly, in pursuit of the low-TX-power problem I discovered 
an unsoldered joint on a relay coil pin, which made contact long enough 
for the initial alignment to fool me well, but then opened up later and 
caused detuning of the preselector/driver filters. Mea culpa.

K2 #5715 now lives, and in perfect operating condition. Cheers!

Marshall, WA3VPZ

Marshall Jose wrote:

> My K2's ALC circuit on the control board oscillates at around 50 Hz
> during receive. During receive, the "V PWR" voltage is set to zero, so
> maybe there's some instability associated with driving U10a into its
> non-linear region.
>
> At any rate, it has no effect on receive operation since the BFO buffer
> the "V ALC" signal controls is effectively blocked further down the xmit
> signal path. But I've noticed that it can cause trouble because when
> it's in that state it won't re-enter a linear mode until the power
> control is increased during xmit above a certain level.
>
> And I've noticed some rather severe limitations on the power I can
> transmit in the higher bands, and have wondered about the words in the
> troubleshooting section: "If you have seen a slow (10-20Hz) oscillation
> superimposed on the transmitter's output signal, it could be due to ALC
> modulation. Increase the value of R98 (RF board) to the largest size
> that permits full output on 10 m."
>
> <http://www.elecraft.com>
>

-- 
Marshall Jose, WA3VPZ