Bruce Griffiths wrote: > Robert Berg wrote: > >> Having seen it discussed, I was wondering whether anyone has actually added >> the Schottky diodes and prescaler chip to a 5334B to provide a C-channel >> input. The matched Schottky quads (5082-2831) are no longer available, and >> even the recommended replacements (5082-2303) seem scarce. Was thinking of >> trying 1N5711s, which can be obtained as matched sets, although probably not >> on my budget. How critical is the need to use matched sets? The NEC >> UPB1507GV-ACT-ND looks promising for the prescaler, if the small form factor >> isn't too minute to handle. >> >> Bob >> WA7ZRX >> >> > Not particularly critical as they are only used as clamps to limit the > input signal to the 30dB gain preamplifier. > You may be able to use a single pair instead, albeit with a lower input > damage level. > Using a quad allows the clamp current to be shared between a pair of > diodes, however some matching is required to ensure effective current > sharing. > Too much diode shunt capacitance will limit the bandwidth. > > Bruce > Quad CR303 acts as a clamp, Quad CR302 acts as a detector with temperature compensation. Only 2 diodes in CR302 are used so CR302 can be replaced by a matched pair.
Try using low barrier microwave specified schottky diodes with lower capacitance than a 1N5711. Bruce _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.