> I have some BB149a diodes (about a 1:2.75 range over 0.5-4.6V, 22pF down 
> to
> 8pF).  I've used a +/- 10% tolerance for the varactor capacitances; the
> datasheet doesn't give a figure for this, but I thought that it was a
> reasonable error margin for reading from the characteristic curves.  These
> diodes work great on the bench and give me my desired pull range.  The 
> results
> tally quite well with my calculated values, but according to my 
> spreadsheet,
> marginal parts (resonators, capacitors, varactors or inverter) will be 
> outside
> my specs.
>
> This is a one-off application, although I will probably build several more 
> in
> future, so there's no real issue adding trimmers; this is a self-imposed 
> design
> (and learning) choice to make the construction repeatable.

For these quantities, rather than a trimmer, it is probably sufficient to 
use a couple of 'SOT' (select on test) capacitors for when the tolerances 
are all off by enough that it doesn't reach the frequency you want. 

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