I switch in about 250 pF to QSY from 3550 to 3850 kHz on my inverted vee.
Jim Thomson wrote:
> My software is not working to do this calculation at the moment.
> What I'd like to know is how much reactance change there is, when going from
> say 3500 khz UP to 3900 khz.
> IE: 68' LL rotary dipole resonant on 3500. I'd like to know how much
> XC there will be on say 3800, 3850 and 3900 khz. Knowing that,
> I can calculate how much C is required in a motor driven vac cap.
> As we move up in freq... the value of the vac cap is decreasing.
> I'm contemplating this scheme vs resonating the rotary dipole at say
> 3900 khz... then switching in various amounts of XL.... with relay switched
> coils, via a mess of vac relay's.
> I'm guessing the rotary dipole, if resonant at 3500, will exhibit 75 ohms
> of XL on 3800 khz ?
> That would imply a 560 pf cap would be required.... and even LESS C... on
> 3900 khz.
> I was contemplating the same thing for the 40M yagi... resonant at 7000
> khz.... and then
> dialing in XXX amount of pf, to resonate it progressively higher up the
> band.. to a max of 7300.
> I have a pair of motor driven 10-1050 pf caps [15 kv, ceramic] . They
> only take 2 secs to get from
> min to max... so tried slowing em down by reducing vdc... which hardlyslows
> em at all [3 x sec's]
> The motor's are 28 vdc.. and stop spinning at 18 vdc. I went to PWM... and
> this works very well.
> Now I can slow em down to a crawl, and maintain almost full torque.
> If i had some aprx ballpark figures to work with for reactance change VS freq
> for both 80+40m
> I can then calculate if this idea is even feasible.
> Tnx...... Jim VE7RF
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