Posted by
Geoffrey Mackenzie-Kennedy on
Jan 20, 2008; 6:33pm
URL: http://elecraft.85.s1.nabble.com/Strange-behaviour-in-K2-tp459483p459486.html
Hello Hans,
The noises which you are hearing on 40m as you tune appear to be very much
like the noises that my K2 #3255 produces, especially above 7100 kHz when
the BC stations are strong, or with a signal generator connected to the
antenna jack. I had started to look into ways to get rid of the problem but
have not had the time yet to complete the job.
I am reasonably certain that the root cause of the problem is the lack of
shielding around the VCO and the 12.xxx MHz Reference oscillator, and / or
the lack of RF filtering of the DC and control lines which enter the area.
It can be demonstrated that a strong received signal will get into the VCO /
Reference area, and at signal frequencies in the 40m band as the result of a
process of mixing a product can attempt to take over the job of the
reference oscillator or certainly disturb the VCO loop causing 'clicks' as
you tune. Sometimes my K2 will lock onto a strong BC signal and only lets go
with a 'whoop' after I have tuned away from the signal a kHz or so - how far
depends on the strength of the BC or generator signal and the frequency.
Although I am unable at this time to suggest a simple cure for the problem,
and a cure might not be simple, I hope that the above will help in some way.
In Northern France my K2 does not 'click' on 40m because the level of BC
signals received there are considerably lower than those received in this
part of Scotland, here the individual carriers can reach -10dbm to -5dbm.
73,
Geoff
GM4ESD
Hans Ostnell <
[hidden email]> wrote:
Hi group!
I have just finished the alignments and tests (part II) in my (second)
K2-project. Sofar all resistance checks are ok, and the results of the
alignment and tests have also been ok. Except for one thing: I think that
the AGC in the radio behaves rather strangely. It's pretty nervous in the
"Fast" position and switching to slow makes it a little bit better, but not
perfect. I have also noticed a "chuffing" or "clicking" sound in my
heaphones while tuning the radio aound on 40 metres. This sound (which
indeed is very difficult to describe) corresponds with the change of digits
on the display (regardless of tuning rate) and is very significant with the
appearance of a strong signal. Tuning the BC-band above 7100 KHz is very
annoying. The behaviour disappears when the antenna is disconnected, but
occours again when connecting a signal generator or other RF-source to the
antenna jack.
Measuring the AGC-treashold voltage on pin 5 of U2 (control board) gives a
range from 2.65-3.74 volts when adjusting R1 from counter-clockwise to
clockwise. The recommended voltage is 3.80 volts, which I never reach. I've
checked the control board very carefully, looking for solder bridges, cold
solderings, incorrect components etc, but everything seems to be fine. I've
even re-heated all solder joints on the control board without success.
Any ideas, anyone?
Regards,
Hans, LA2MOA
K2 #6341 - unfinished
_______________________________________________
Elecraft mailing list
Post to:
[hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help:
http://mailman.qth.net/subscribers.htmElecraft web page:
http://www.elecraft.com