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Author Topic: Photos of Tarheel coil and form?  (Read 2910 times)
N4HNO
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« on: March 01, 2012, 06:44:49 AM »

Does anyone have a photo of the coil and form inside any of the tarheel antennas?  I am familiar with the Hi-Q system and wanted to see what they used on the tarheel line.  Do they use fingerstock for contacting the coil or some other method?

73's

John
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K0BG
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« Reply #1 on: March 01, 2012, 09:57:01 AM »

It is finger stock, but it isn't beryllium like almost everyone else uses. The coil form itself is a low loss phenolic. As screwdrivers go, it is about average, except for their Lil Tarheel. In that case, the coil, and motor are about as minimal as they come. Yet, the Lil Tarheel is their most popular model.

At least two manufacturers literally use a spring to make contact with the coil. A couple use a longitudinal contact assembly, rather than the more-common radial one.

One common misnomer about screwdriver antennas, is the belief that since the coil is not short tapped (like the HiQ), the Q will be higher. However, they are essentially short tapped by the capacitance between the outside surface of the coil, and the inter surface of the mast. If the gap it too large, circulating currents in the unused portion of the coil will cause an arc to occur, which can destroy the coil. At least two screwdriver companies have bit the dust for this reason.

The HiQ has its own set of problems too, not the least of which is cracking in the coil assembly, and water collection in the mast.
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KE4DRN
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« Reply #2 on: March 01, 2012, 06:52:38 PM »

hi,

photos of a similar antenna but it is not a Tarheel

http://www.k4eaa.com/screwdriver.htm

the Tarheels use a fiberglass tube for the coil form
and contacts used in the decoupler is a custom die cut
beryllium copper high-pressure finger stock.
Pitman motors are ball bearing high torque series
12VDC gear reduction drive.

http://www.tarheelantennas.com/why_a_tarheel

73 james
« Last Edit: March 01, 2012, 09:35:15 PM by KE4DRN » Logged
M6GOM
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Posts: 884




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« Reply #3 on: March 02, 2012, 12:09:55 PM »

K0BG your post needs changes to reflect the reality of Tarheel construction.

He is biased towards Scorpion antennas, Icom 7000s and BetterRF screwdriver controllers.
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W9PMZ
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« Reply #4 on: March 02, 2012, 01:07:31 PM »

I live in Ohio where we have winter and summer and extremes inbetween.

I have had 3 different models of the HIQ antenna.  Never had any cracking, water intrusion or any issues with the antenna.

My take on the advantage to the HIQ antennas is that the overall height of the antenna does not change.  There is a coil contactor that travels up and down inside the antenna, as compared to the opposite of the coil moving up and down in contact with the contactor.

I have also owned Tarheels (Model 200) as well.  I was always a little worried when on 75M and all of that coil came out and above the lower part of the mast.

73,

Carl - W9PMZ
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N4HNO
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« Reply #5 on: March 06, 2012, 06:35:13 AM »

I had purchased a used Hi-Q. I basically loved it.   Unfortunately, UPS dropped something big and heavy on the box.  It was reasonably packed, but the coil lexan was cracked.  I could have gotten it fixed-but it would have been more than the price of a new antenna at that point.   It's nice that they don't change length.  I think that the DK-3 type of design that has a coil wound on a form might be tougher in some ways, with some disadvantages too.  The newer Hi-Q's look nice with the silver plated balls and the round contactor puck.  I guess the Hi-Q's have a coil wound onto a form then unwound into the lexan cover.  It's the only way I can think of they could make it that way. 

People want different things.  I saw a Scorpion that looked like an  three inch diameter  and 7ft. long irrigation pipe strapped to an F-350. I have a minivan.  I have to make some compromises.  Since I have two small kids I want the antenna on the roof to keep any possible exposure to rf to a minimum. People will say that I am being too extreme.  I don't care.  Basically I am limiting myself to lower power, and smaller roof mounting for a more important reason-safety.  Right now I am mounting a shorter Hustler whip on the roof with a 1/4" steel bracket.  It is what it is.  I am interested in homebrewing a screwdriver  at some point.  I do think it is interesting that Tarheel doesn't post photos of interior construction of their antennas.
73's
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K0BG
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« Reply #6 on: March 06, 2012, 08:48:11 AM »

There is nothing wrong with Tarheel antennas. They are presently the largest selling brand on the market. No one comes close, except for the ATAS from Yaesu. Their most popular model is the Lil Tarheel. Biased or not, they're a minimal antenna as is the ATAS. People buy them because they're small, easy to mount, and they're spousal approved. Performance wise, they average 15 dB to as much as 25 dB down from a decent screwdriver, the Scorpion notwithstanding.

Everybody has a choice as to what level of performance they're willing to settle for. As long as some contacts can be made, especially DX ones, that seemingly is all that counts. But that's not me.
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WX7G
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« Reply #7 on: March 06, 2012, 08:50:37 AM »

N4HNO, the Hustler on the roof will work fine. The radiating length of your antenna installation is measured from the bottom of the automobile chassis to the top of the antenna. The automobile body can radiate more than the "antenna" does.

You may have a better signal than if you mounted a good Screwdriver antenna on the bumper. When mounted on a bumper there is current cancelation due to charge flowing upwards in the screwdriver and downwards in the automobile body. The part that contributes to radiation is then only the portion of the screwdriver protruding above the top of the automobile. Mount an 8' screwdriver antenna on the bumper with 3' protruding above the roof and you have a 3' antenna (with the low radiation resistance of a 3' antenna).

I use an ATAS-120 mounted on the roof. How does it compare to something like a large screwdriver? Based on measured base impedance, SWR bandwidth measurments, and simulations my ATAS-120 installation has a radiation efficiency of 10% on 40 meters. Compare that to a roof mounted Tarheel 100HP with 30% radiation efficiency and the difference is 5 dB. On the higher bands the difference is even less.

Where a mobile antenna is mounted can be more important than the mobile antenna itself.

How can one get 15-20 dB of difference between a good Screwdriver antenna and a Hustler or ATAS?

1) Compare them on 80 meters
2) Bumper mount them

Bumper mounted the radiation resistance is reduced, the antenna current is higher, and the loading coil losses are increased. Given the loading coil Q of 100 for the Hustler and the ATAS and 300 for a good Screwdriver the screwdriver wins by a good margin.

As we move up in frequency the efficiency differences between the two antennas decrease greatly.


« Last Edit: March 06, 2012, 09:12:07 AM by WX7G » Logged
KE4DRN
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Posts: 3721




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« Reply #8 on: March 06, 2012, 07:29:34 PM »

hi,

if anyone has quesitons on the Tarheel antenna,
Robert NC4RY can answer them.
He may send you some photos of the internals.

When he started selling them at local hamfests,
you could see the internals compared to other
makes available at the time.

tarheelantennas@aol.com

They are well made, I got a deal on a used Jr,
I took it apart and cleaned the gearbox on the motor.
The antenna must have been under water for a time.

It works great, I also have a model 75.

73 james
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