With the generous help of Gary and Wayne I have fixed a problem that has been
bugging my KSB2 since I built it.
I had been getting a variation in the amount of mic audio needed to trigger the
VOX. Also very intermittently (with VOX selected) my K2 would go on to transmit
and stay on until I switched the main power on/off.
For VOX operation this IC sets the VOX threshold voltage on the VOX comparator
U4. The voltage on U3 COMP OUT is measured by U1 and the DAC is set to give an
voltage differential between Pins 2&3 of U4. This differential voltage depends
on the setting of mic gain (SSBA). With the latest version of KSB2 firmware
V1.08 the values are approximately SSBA 1&2 = 75mV and SSBA 3 = 50mV.
The problem was a bad DAC IC U2 (MAX522), which was giving random threshold
voltages. Changing the IC cured the problem, and my VOX now (with the Anti-VOX)
works sweet as a nut...
73
Stewart G3RXQ
_______________________________________________
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
Locked
