If he puts two diodes in parallel he will double the capacitance and
will have to reduce the amount of inductance to have the same
min. frequency. Im not sure that the high end won't be greater than
before, even though the capacitance ratio is the same, since the
fixed inductance is lower.

Another idea would be to put the two varicaps in parallel, but switch
one of them out as you approach the upper frequency.


Kenneth,

F=1/((2*PI)*SQR(L*C))

If you double C, you have to halve L to maintain the same frequency. If you
do this, you only changed the LC ratio, not the delta tuning range.
The only way to get more delta F is to get more delta C. If you use the
switching technique, you'll have a discontinuous tuning curve (Vtune vs
Freq) which makes it hard to implement a closed loop tuning system. It can
be done, but the control loop gets complicated.

A previous poster suggested what I'd called a "synthetic reactance", which
is a series-parallel LC combination. This technique can produce very large
effective-capacitance changes with a modest varactor range, however it also
comes with the susceptibility of mode-jumping in the output frequency.

Joe
W3JDR