[time-nuts] Adding prescaler to HP 5334B

[Bruce Griffiths]

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