mobile cap hat question...

[mr_fx]

ok so my current setup is as follows:

2.4mm wire, 2.4mm spacing, 31 turns around a form that is about 89m

the 3.5 foot mast, with about 6" hook up wire under the coil and a 52" stainless whip above the coil...

currently this setup will tune as low as 6Mhz on the dot

how big of a TOP mast and cap hat would I need to tune the existing setup into the 75/80m band?

My understanding of cap hats is limited

I think the existing coil is about 60uF @ 3.5Mhz

I do have room to add an addition coil near the first coil if I REALLY needed to

I use the #8 tap on my existing coil for 7.0Mhz if I calculated this correctly that should be about 40uF (which is about on target for a 40m, 9ft, center loaded whip...)

but I think I would need about 160-200uf to pull off 3.5Mhz with my current whip...

CAN a cap hat and say a 2-3 foot tall (TOP) mast with a 60uF (@ 3.5Mhz) coil achieve resonance?

 

[W5LZ]

Add a couple of feet to that starting top whip and you would probably get into the 80 meter range. That would be a lot simpler than trying to use a cap-hat with a much shorter top whip. Can it be made to work with a 2 foot top whip, your loading coil, and a top-hat? Sure, but count on a fairly large cap-hat, maybe 3 - 4 feet in diameter?
Where you mount that cap-hat can make a huge difference. It should be at least the length of the loading coil -above- the loading coil, with a whip on top of it. If it's on the top of the loading coil it's much less affective because it sort of 'nullifies' part of the loading coil.
Something you might try with the starting description antenna is to tie a guy line from the top whip to the door post? Add a length of wire down that guy line connected to the top-whip, it'll act as a cap-hat. See what various length affects the resonant frequency, how far it will lower it.
Lots of possible ways to lower the usable freuqncy, but a cap-hat and a shortened top whip just isn't a very good way of doing it.
- 'Doc