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Jorge:

200 pF. is too large a range for a 300 KHz VFO.

Assuming 200 pF as your capacitor and about 30 pF. stray capacitance,
The L value for 2.7 MHz is ~15 uH, as noted.

But if your capacitor has a minium value of about 20 pF, the same
15 uH will give you a high frequency of about 6.5 MHz.

You should use a much lower variable cap for that range, maybe 60 pF.

Better yet is to use a varicap and ~12v supply to the capacitor. That will
give you the range you want with less fuss (and probably much more stability).
Search for a Colpitts varicap oscillator for the details. It will involve using a
potentiometer. A 10-turn one is best, or even two for tuning and "bandspread";
a 10-turn main and one-turn fine tune pot.

On the other hand, if you are already using a 200 pF capacitor on 20m, a proper
inductance for 40m would be one about twice the value of the one you are already using.
Everything else should work out to be about the same. Of course, you will also need to change
the PBF and LPF as well. use the same procedure -- double the present 20m values for 40m.
That will put you in the ballpark.

john
AD5YE

Sorry, guys.

The above calculation for the 20m rig assumes the same IF. If they are different,
the L value must be calculated for the new VFO coverage,
using f^2 = 25330/ LC where f is in MHz, L in uH, and C in pF.

The same general considerations apply.

john
AD5YE

That is a good source for a pre-exixting rig. Note that it
refers to a varicap VFO. Note also that the BFO has to be changed
somewhat to accomodate the change in sideband.

I actually did this with a BITX v.3 and it worked well right out of the box on 40m.
My IF of ~11.059 MHz remained the same, of course.

john
AD5YE