I believe that you would be proven correct about the RF feedback. My thought about a tin box totally enclosing the PCB stems from an observation that the skirts of the varicap "controlled" filter set for say 700Hz bandwidth are a little wider with the KSB2 installed than when it it is not, and noticeable from approx 40db below passband on down. I made no measurements because I was Birdy hunting/killing at the time. If this blow-by is due to leakage between P2 and P3 or through the switching diodes (off) on the KSB2, then the tin box would have little if any effect. But the KSB2 does come close to forming a bypass route just due to its proximity to the post mixer amp, RF board filter etc, and my gut feeling is that a box around the KSB2 or its replacement would be a good start. The box would also help to keep out the RF from nearby oscillators.
73, Geoff GM4ESD On Wed.2nd March 2005, Stewart G3RXQ wrote: Any form of increasing the mic gain internally (eg rf speech clipper) needs to be carefully thought out. The microphone signal routing and earthing from the front panel socket thru the RF board and into the KSB2 is far from ideal. Common mode, series mode - the lot - RF feedback is the likely result. A groundplane board with the crystal filter laid out to reduce blow-by may be the way to go. A tin can over the whole assembly may help. The biggest hurdle to overcome in making changes to the KSB2 is interfacing with the existing firmware which is far from straightforward. 73 Stewart G3RXQ On Wed, 2 Mar 2005 08:11:54 -0000, Geoffrey Mackenzie-Kennedy wrote: > Intersting ideas. If you did enlarge the SSB board to get all the bits in, > > in which directions would you enlarge the exixting board? > IMHO it would be essential to contain the "new" board in a 'tin' box in turn > mounted on metal, which raises the question of access to test points etc on > the RF board, but a solution might be available. > _______________________________________________ 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
