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## Re: [TowerTalk] How much reactance change on a dipole, from 3500-3900 k

 To: Jim Thomson Re: [TowerTalk] How much reactance change on a dipole, from 3500-3900 khz ? "Richard (Rick) Karlquist" Mon, 05 Jul 2010 08:04:17 -0700 mailto:towertalk@contesting.com>
 ```I switch in about 250 pF to QSY from 3550 to 3850 kHz on my inverted vee. Rick N6RK 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 > > > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] How much reactance change on a dipole, from 3500-3900 khz ?, Jim Thomson Re: [TowerTalk] How much reactance change on a dipole, from 3500-3900 khz ?, Richard (Rick) Karlquist <=