When the motor moves to tune the tarheel screwdriver antenna, does the outside height change or is all the movement internal and the outside dimension of the antenna does not change.

If it does not change size, can someone post the dimension from the base to the bottom of the whip.

If it does move can someone post the dimension from the base to where the whip screws in at the minimum size and the mazximum size.

Thanks.

I did a new install in my truck with a Wold River Manual Coil and want to see if a baby tarheel will fit.

I mounted the coil in my bed to the toyota rail system, grounded it to the bed with a short wire, attached a wire where the whip is supposed to attach, ran that wire through a hole in the fiberglass  where I took a bolt out for the rack and attached that wire to a mount that holds the whip on the top of the rack. I took out the shield / Conductor insulator so that the whole mount is part of the radiator / whip.

It seems to work well. I great great resonance on 80, 40, and 20 meter bands with resonance impedance from 54 to 74 ohms depending on the band with no reactance.

This seems to work very well and the manual screwdriver is out of the weather.

I want to know if I can mount a tarheel or a ATA-120A in the same way. If the tarheel gets taller and shorter i probably cant do this.

Here are pics of the install.

yes I know I need to wash my truck. It's a truck.

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I don't have a Tarheel but I have several other mobile "screwdriver" antennas including the ATAS-120

When you go lower in frequency, the length of the whole thing gets bigger. It extends.

That is where the term: "screwdriver" comes from. You have a motor in the antenna that moves that outer section up and down on the coil The first guys that did this, used an electric screwdriver for the motor.

If you pay close attention; you can see this here:

If you measure the length of that clear outer cover, that is APPROX how much longer it gets from the highest frequency it tunes, to the lowest frequency it tunes.

thanks

i figured it probably did change size

mine is a TARHEEL II

it gets longer as you go lower in frequency

If I'm picking up what your trying to lay down with your mobile setup I would pick up a sgc or icom antenna coupler.

My tarheel works much better than my icom AH-4 did

Yeah but your tarheel isn't under a camper shell.

how much RF attenuation do you think the fiberglass has ?

I am guessing about the same as the lexan cover on the coil

Touche. There us metal around the windows and on the roof but that wasn't in the consideration for my previous comment

OP... a dummy load has great SWR and is not all that good as an practical antenna, so how well does this setup actually work for you?

good point  LOL



My TARHEEL II is 19" - 26" from the base of the antenna to the start of the whip.

.

If it were just fiberglass, without metal window frames, and cargo racks, it would work pretty well, I think.

Look at how many antennas are fiberglass

It still might work really well.

that RF's gotta go somewhere

that is what I dont know yet.

using the wolf coil and the whip that I already had is a proof of concept before I buy a tarheel.

i had about an hr yesterday and the conditions sucked. So I still have to figure that out. The coil does resonate  well on different bands. it has been my exoerience that coupling to metal will interfere with that, So I am hopefull this will work, but I dont know yet.

it might or it might not

the bandwdth on 20m is the whole band.

from 14.0 to 14.35  it resonates with zero reactance and from 54 to 75 resistive ohms  from low band to high band

so it may very well be a dummy load

or

the metal of the window, the rack on the roof and the cross bar might be acting as a capacity hat increasing the bandwith. 40 and 80 has a much smaller bandwidth without moving the coil.( after moving it for the bamd)

It all depends on if anybody can hear me. I should have time tomorrow to check that out

a lot of installations have the mast and the coil well below the metal and close to the cab or on a hitch, below and close to the metal of the tailgate and they work so this might too

It looks like it works, fairly well.

It is hard to make a quantitative assessment without a field strength meter or antenna current meter ( had one of those MFJ ones but it was inop so i returned it for a refund)

But I did make a QSO underway into Eastern EU with a 57 report on 20m, but I have done that with a hamstick too.