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Spiral, 1/2 wave dipole -- probable radiation pattern?

 
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StevieW
Antenna-Theory.com Newbie


Joined: 03 Sep 2014
Posts: 1
Location: SD, CA

PostPosted: Thu Sep 04, 2014 2:52 am    Post subject: Spiral, 1/2 wave dipole -- probable radiation pattern? Reply with quote

Hello,

I'm a HF newbie planning on putting together an amateur station.

One intriguing antenna product I've encountered is the TAK-tenna [http://www.tak-tenna.com/ ]. It is a 1/2 wave dipole spiraled on two 'wheels' on either side of a ~40 inch boom. Essentially it looks like a 'dumbbell' with the lead attaching at about the middle of the boom.

Numerous reviewers have given favorable remarks. Its lightness (8 lbs) and compactness are attractive to me.

But, I am wondering what sort of radiation pattern such an antenna might produce?

They have an 80 m and a 40 m model with quarter wave wire lengths on each of the end-cap spirals, cut, I assume, for about 5 MHz and 10 MHz, respectively.

And, two mounting orientations are discussed, Horizontal, with the spiral wheels perpendicular to the ground, and Vertical, with the wheels parallel to the ground. Do either of these mounting orientations suggest a more or less 'directional' capability?

Though I am very new to exploring HF equipment, I do know that such an antenna would require a tuner to work on multiple bands. And, I know that antenna tuners are more correctly 'impedance matching' devices. The standard 'in shack' tuners make the lead line impedance match that of the transmitter, so the transmitter will be able to give its full (chosen) power to the lead, and also prevent HF SWR from flowing up the coax lead back into the station.

But, the in-shack tuner does not address long feed line loss, or address impedance of the antenna itself. So, full chosen power is offered to the lead, but the antenna may still radiate inefficiently.

I'm considering a remote, automatic tuner which attaches at the antenna. From my limited understanding, the remote automatic device has much better chance of making the most optimal match, and, because it is at the antenna, a better portion of delivered power to actually radiate through the antenna.

Any opinions on remote/automatic v. in shack tuners? (and, are my assumptions correct?)

Any advice you can offer would be greatly appreciated,

Thanks,

Steve
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bigSteve
Antenna Wizard


Joined: 14 Mar 2009
Posts: 265

PostPosted: Sat Sep 06, 2014 7:49 pm    Post subject: Reply with quote

That antenna is basically a short dipole antenna, so the radiation pattern will be similar to a short dipole (sin[theta] pattern). Think of a dipole with the arms wrapped up in spirals so it is shorter.

On mounting: that will determine if you have horizontal or vertical polarization. If the spirals are vertically mounted (like a dumbell on its edge it is vertical). If it like a car axle, it is horizontally polarized.

Yeah, you'll need to do impedance matching or tuning to change bands on that. You could also make it longer or shorter. I don't think there is a generic "impedance tuner" that would exist, it is specific to the antenna and situation at hand.
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