I have a question about the receiver front end protection circuits in the K3 — specifically, the ones on the RX ANT IN and AUX RF inputs.
When I went to the schematics, here's what I found: AUX RX feeds the KRX3 Sub Receiver board, where it goes to a gas discharge tube (SA1) shunted by 470K. THe voltage there (schematic name RF SENSE) then goes through a 2 pF coupling capacitor to a Schottky Barrier Diode assembly driving a Darlington relay driver. The base of the Darlington is shunted by a 470K resistor in parallel with a 10 uF capacitor. RX ANT IN is on the KXV3 Connector schematic. It goes to a SPARK GAP (GAP1), shunted by 100K. That voltage then goes to C1, a 2 pF capacitor driving an identical Schottky Barrier Diode pair and another Darlington circuit. The base of *this* Darlington is shunted by a 1 Megohm resistor in parallel with a 0.1 uF capacitor. So.... Is GAP1 the same as SA1? If so, and ignoring the difference between 470K and 1M, why is there a factor of 100 difference in the capacitors in the Darlington drive circuit? It seems to me it's going to take 100 times as much charge to forward bias the base of the AUX RX Darlington as it is the base of the RX ANT IN Darlington. Is there a reason for such a huge difference? I ask because the RX output of my electronic (vacuum tube) TR switch keys the RX ANT IN COR but not the AUX RF COR. Bud, W2RU ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
