CAPACITOR KnowledgeBase

[flintstone mop]

Hello Folks
I'm nearing the final stage of a remote antenna tuner. The WX is changing toooo DAM fast for me!!!
I have to determine if I need more capacitance or less. The vac variable is at the end of its travel. I'm on the higher end of 160M 2. something mhz. Looking at the cap shaft It's turned fully clockwise. I cannot see the movement of the elements inside.
I DO have two other vac variables that I can see the meshing action. My state of confusion is....when the plates are fully meshed............is that MAX capacitance? Would all vac variables move the elements inside the same direction?
  
BS about the remote tuner and Rebirth of the short vertical.
I can parallel another vac variable to give me more PF's. I don't want to tag on those smaller units and changing values when heating occurs. I have room in the box for the additonal vac variable. I don't know if there will be enough adjustment to travel the entire 160M band. I built the tuner with a variable inductor to go across the feedline for a matching option, but the present system seems like it wants more PF's and give me 50 ohms with a low reactance without the inductor. I am at the hairy edge of the 160M band. I could shorten the antenna "stinger" above the loading coil. There's so many ways to do this. It's mind boggling.



The previous version of this vertical needed the coil across the feedline to give some sort of transformer action. The new location plus 80 radials and a capacitor in series with the feedline wants to give a match without the coil.

This configuration of a cap in series and coil paralleled with the transmission line worked very nicely with the Unihat vertical, which was another short vert and was very effective on 160M.

[KM1H]

I DO have two other vac variables that I can see the meshing action. My state of confusion is....when the plates are fully meshed............is that MAX capacitance? Would all vac variables move the elements inside the same direction?

Yes to both Fred. The later ones are ceramic instead of glass and you dont have the option of guessing.

If the antenna is too long you want a series cap. If its too short you want a series inductor. Those are strictly to obtain resonance. You will then have a reactance of zero and a pure resistance of some low value under 50 Ohms which you will now have to transform up. This can be done with coax matching sections, a unun of correct ratio, or a LC section.

A short antenna will be narrow bandwidth so if you want to cover the full band you will need an ATU in the house or at the antenna.

Carl
KM1H

[flintstone mop]

OK Carl, It seems that if the capacitor is trying to lengthen the antenna, then I'll tilt it over and adjust the stinger rod to shorten the antenna. This is the Cushcraft MA160 160M vert 27 feet high.
It's  a "top loaded" antenna.

Fred