[Elecraft] Strange problem when switching modes from VFO A to

[Mike Scott]

>I have VFO A programmed for CW on each band, VFO B programmed for SSB.
Power up the K3 on VFO A then switch over to VFO B and the signal generated
is extremely distorted and sounds like it is being transmitted via a very
narrow filter.  To correct this problem simply switch the mode from L or USB
to CW and back again to L or USB. 

>Any suggestions ? >Jack, W3TMZ


Jack,
I sometimes come up with the same pinched audio that you are reporting. My
situation is not as repeatable as yours. I have the same VFO A and VFO B set
up as you do for CW/SSB. When my pinched audio has occurred I believe it
happened after an operation just like you describe by switching over to VFO
B. I tend to correct the problem with a power-off reset and haven't tried
your mode-change solution. 

For what it is worth, this problem has been reported a few times by me and
one other person that I know of. It has occurred over multiple firmware
installations. My problem seems to have not occurred in quite some time now,
ever since I enabled the noise gate function. Since Elecraft has been unable
to duplicate the problem they are of course stuck. They have been diligent
in trying to replicate the problem. If you have not enabled the noise gate,
try it and let us all know if you still have the problem. I am wondering if
the noise gate is causing the state of the audio path to be different such
that it avoids the issue from surfacing.

One other tidbit, perhaps unrelated but I pass on just in case it is
related. I notice that when the K3 powers up in SSB mode (2.7 KHz filter)
that the receive audio initially comes up in a narrow band pass and then
shifts to the 2.7 KHz filter bandwidth. I am wondering if the transmit audio
is in a similar sequence and gets stuck in a narrow pass band and the
startup sequence on the transmit side never completes until a mode change.
Here is the start up sequence as seen through the receive side:

1. Hit the power button at time zero

2. Audio comes up in a band limited to approximately 450 Hz to 850 Hz at
roughly 2 1/2 seconds after sequence starts. The band limited phase lasts
maybe a half second or less. I note that if we tried to transmit through
that kind of band pass filter the audio would indeed be pinched.

3. Then broadband audio comes up through the 2.7 KHz filter with AGC wide
open at 3.4 to 3.5 seconds

4. Then normal audio with under AGC control after 3.6 seconds (the 100 msec
or so at the end of the sequence seems to cause the noise blast that some of
us have been reporting, Elecraft is testing a change to this right now).

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
K3-100 #508/ KX1  #1311