In a message dated 30/06/05 13:35:58 GMT Daylight Time, [EMAIL PROTECTED] writes:
I also see that Q5, the transistor that shorts out the output filter tank, has no bias at all. There is no DC return for the base to ground. Is this correct? Maybe the base should not be floated? Maybe Q5 is open? Reply:------------------------------------------------------- Rich, Q5 on the KNB2 is either on or off, there is no in-between state so no bias is applied to the transistor apart from when it is switched on by the one shot Q3/4. Possibly looking at the base and collector of Q5 with a scope would help to see the spikes of enabling voltage and suppression of the segment of signal during a short duration noise burst. The circuit details with the schematic on the last page of the KNB2 manual should give an insight into the method of operation. The problem with checking most noise blanker is generating the necessary test conditions to see if the operation is correct. Most radio equipment manufacturers are rather vague in this respect and I have yet to find a piece of test equipment that will provide interference pulses on demand. Possibly an automobile spark plug driven by an ignition coil and contact breaker pulse source may be the answer. Have tried using electric drills and other brush motors for generating noise pulses with only limited success. Otherwise it is sometimes a case of awaiting a RF noisy auto to go past as the KNB2 only functions on short duration spikes of noise. Regards, Bob, G3VVT K2 #4168 with KNB2 _______________________________________________ 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
