Search for varactor 10 ~ 1.8pf

[Pierre-François \(f5bqp_pfm\)]

Hi,

I'm searching a replacement to the ZC800 varactor with the following caps
specs:
2v ===> 10pf
20v ===> 1.8pf

It's to equip a 350 ~ 500Mhz VCO (0v ~ 9v)

I've tried a BB405B but its capacity is too high at 9volt the maximum
driving voltage at its upper frequency so the max frequency is 460Mhz, not
500.

Many thanks for your help.
pf

 

[Pierre-François \(f5bqp_pfm\)]

Add a small capacitor between the varactor the the inductor to reduce
the capacitance. You could use a small trimmer capacitor to make it
easier than trying to S.I.T. Sometimes it is the only way to do a one
off repair.

Hi Michael,

Many thanks for the nice idea, I'll try it if I don't find a replacement.
I'll still search for a while, before I try.
I would prefer no tuning... However may be it's "Impossible Mission"...

pf

 

[Baron]

Michael A. Terrell Inscribed thus:

You can use the variable, then unsolder it, measure it, and use a
fixed value capacitor if one is close enough to the measured
capacitance.

Another way is the old fashioned 'Gimmick Capacitor' which is a
pair
of insulated wires that are twisted together, then trimmed with a pair
of wire cutters to get the value you need. Then there is no problem
with the value changing by accident. They were common in early
electronics, in RF circuits.

Yes I remember that trick ! A variant to get very low values was to
wind a coil on the insulation of a straight wire. One advantage of this
was that if the coil was grounded it provided a screen as well.