K3 AGC Mod Results

[Dennis Egan]

I performed the AGC mod as suggested by Wayne N6KR in his "K3 Hardware
AGC Experiment shows promise"
posting on Dec 4.  The mod was to add an additional 1 or 2 uf of
capacitance onto C238 on the Main Receiver
PCB.  I obtained my own SMT caps from Mouser, and for 76cents and 30
minutes of time the mod was made.

Initial testing with the mod at my house was done between the Main and
Sub Rx; the Main had the mod, the
Sub didn't.  From perusing the schematics, it appears that they have
different AGC systems.  The signals on the
Main Rx seemed to have a slightly purer CW note; the effect of the
pile-up "mush" also seemed to be less
evident.  Not wanting to jump the gun, I decided to take the modified K3
down to a station with a big 160M array
and test out the mod there.

I set up two K3s identically with AGC settings, and fed them with the
same antenna signal.  I did modify my
signal path from the original write-up; the Main Antenna went into Ant 1
of K3(1), out the Ant Out to a splitter,
the to Ant In of K3(1) and K3(2).  I protected the front end of both K3s
by putting both into transmit when I
transmitted (using a macro into the N1MM messages for K3(2)), and put
K3(2) into TEST mode so I didn't accidentally
put any power out of K3.  I also recorded the contest, with each K3 on a
different channel so that the audio could
be readily compared.

My results mirrored those of my preliminary tests with the the Main and
Sub Rx; the mod provides a small but
noticeable improvement in pileup situations.  All cw signals seemed to
have a slightly purer note to them.

After my original posting, several ops suggested I use a SLP setting of
7 or 8, to get more AGC action.  I decided to
keep my SLP setting at 0, as that has been my normal setting for
awhile.  I also felt that if I got an improvement
at that setting, it would be even more noticeable at a higher setting.  
I did plan on changing the setting after several
hours of operation, but never got the chance; I operated a little less
than 3 hours.  The amplifier decided it didn't
like the antenna, and kept faulting off.  After spending an hour trying
to figure out what the problem was, I gave
up and went home.

If anyone would like an hour worth of audio, send me an email.  The
unmodified K3 is on the left channel, and
the modified K3 is on the right channel.

Dennis W1UE




______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html