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: [email protected] 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.htm Elecraft web page: http://www.elecraft.com
