[time-nuts] Noisy varactor diodes

Didier Juges shalimr9 at gmail.com
Wed Dec 19 21:33:21 UTC 2012


Actually I have had better success with Zener diodes. The 1N47xx series in
particular I have used up to VHF with good results. Take a diode with a
zener voltage specification 20% above your operating voltage and it may
just work.

Didier KO4BB


On Tue, Dec 18, 2012 at 1:51 PM, Robert LaJeunesse <
rlajeunesse at sbcglobal.net> wrote:

> Corby,
>
> FWIW many power rectifiers can be used as decent varactor diodes. The
> MV840 is
> nominal 100pF at 4V with at least a 2:1 ratio (2.18 typ) from 4 to 25V. The
> Vishay FGP50D-E3/54 is typically 100pF at 4V and drops to a shade below
> 50pF at
> 25V, or just over 2:1. Good news, it is in stock for $1.32 each at Digi-Key
>
> http://www.digikey.com/product-detail/en/FGP50D-E3%2F54/FGP50D-E3%2F54GICT-ND/2832954
> .
>  This part is but one example, there are others with similar
> characteristics.
> The Fairchild SB1100 is typically 110pF at 4V and drops to a shade below
> 50pF at
> 25V, again just over 2:1. It's even cheaper at $0.52 each in singles.
>
>
> Unfortunately I can't speak for noise, but these are newer technology parts
> and may be clean and linear enough to work as a sub, especially since
> there are
> 3 other MV840s in parallel.
>
>
> Even if only for a test, Hope this helps.
>
> Bob
>
> p.s. I've been known to raid dead PC power supplies for diodes not unlike
> these.
> But then you'd have to look up data sheets or measure the capacitance with
> a
> bridge somehow.
>
>
>
> ________________________________
> From: "cdelect at juno.com" <cdelect at juno.com>
> To: time-nuts at febo.com
> Sent: Tue, December 18, 2012 1:32:11 PM
> Subject: [time-nuts] Noisy varactor diodes
>
> I was recently repairing a noisy A3 module for an HP 5065A.
> ...
> Anybody know where to get an MV840 ???
>
> Thanks,
>
> Corby
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