[time-nuts] Noisy varactor diodes

Robert LaJeunesse rlajeunesse at sbcglobal.net
Tue Dec 18 19:51:19 UTC 2012


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 
 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.


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 ???



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