On Sat, 13 Dec 2003 23:27:24 GMT, "W3JDR" wrote:

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.

Suppose you mean greater Cmax/Cmin, larger delta C was already
achieved above, but as you say "it doesn't work"
The tuning range can be calculated as follows:
(Cmax/Cmin)^2 = Fmax/Fmin

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.


Joe
W3JDR


You could always divide the tuning into two ranges and it shouldn't be
too difficult to adjust the trimmer capacitors

73
LA8AK
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