[time-nuts] Adding prescaler to HP 5334B
Didier Juges
didier at cox.net
Mon Mar 31 23:27:16 EDT 2008
I don't believe these are RF detectors, they look like switching diodes.
Even though they are Shottkys, the spec says they have a 5nS reverse
recovery time ???
That would be too slow for a 1 GHz counter.
I use a lot of BAV99, and while not being Shottkys, they have about the same
reverse recovery and 15% of the capacitance.
Didier KO4BB
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Keith Payea
> Sent: Monday, March 31, 2008 10:05 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Adding prescaler to HP 5334B
>
> My usual choice for dual schottky in an SOT-23 is the BAT54.
> It comes in four flavors:
>
> BAT54 - single diode
> BAT54A - Common Anode
> BAT54C - Common Cathode
> BAT54S - Series
>
> It's rated at 30V/200mA.
>
> Keith
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Didier Juges
> Sent: Monday, March 31, 2008 7:56 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Adding prescaler to HP 5334B
>
> I was thinking of buying a few dual shottkys (series configuration) in
> SOT-23 package and I thought it would be a piece of cake
> finding those, but interestingly, my usual part vendors
> (Digikey, Mouser, Newark, Allied) don't carry any that I
> could use, at least if they do, I did not find them.
>
> Anyone has recommendations for such an animal?
>
> Didier KO4BB
>
> > -----Original Message-----
> > From: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
> > Sent: Monday, March 31, 2008 8:37 PM
> > To: Discussion of precise time and frequency measurement
> > Subject: Re: [time-nuts] Adding prescaler to HP 5334B
> >
> > 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
> >
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