> 1. I used the formula LC=25,330/f squared to come up with a place to
> put the inductor tap for 3885khz. I picked the middle of my known cap
> tuning range (250pf) and calculated I needed 6.37uh of inductance,
> re-tapped my inductor proportionally, and found a good dip with my grid
> dip meter nearly right on. Question: Should I have picked a different
> capacity that would have used less inductance? My method doesn't seem
> too scientific to me and maybe it is just outright incorrect.
According to the W5FD formula, for 4000 volts @ 700 ma, you need 22uh
on the Pi coil and 4.8uh on the "L" coil. I would toss the 2nd harmonic filter,
as you will be plenty safe with this circuit. C1 will be 105 pf, and C2 will be
625 or a little more on 3885.
> 2. If I am just using these two frequencies for now (possibly 160mtrs,
> 1885khz later) how do I figure what I need for loading capacitance and
> where should I tap my series loading coil (15uh)? Should I just set the
> cap at the lowest or highest end when I strap whatever extra capacity is
> needed and then do some sort of calculation based on frequency to figure
> out where to tap the inductor?
I would cut the tank inductor off at the 45uh point. This will set you up for
160m
later, and tap it in the center of what is left for 80m. Cut the L coil down to
9.4uh
and tap it at 4.8uh for 80m. If you don't remove the excess turns on the tank
coil, be sure and thoroughly short out the excess turns to prevent the thing
from turning into a Tesla coil on you. C1 on 160m will be 210 pf and C2 will be
at least 1200 pf or more.
> 3. Should I just toss the suppression trap out of the picture? I want
> good harmonic suppression so is there a formula I can use to implement
> its use in this circuit? Obviously I'll have to change it if I go to
> 160m later on.
Suppression will be probably be better than your exciter with this Pi-L
circuit...toss it!
Sounds like a great project...I can't wait to hear it!
(((73)))
Phil, K5PC
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