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Author Topic: H-pole antenna  (Read 2165 times)
AE5EK
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Posts: 53




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« on: April 03, 2013, 07:42:36 PM »

I found this antenna and it seems too good to be true based upon the great radiation patterns.
http://www.qsl.net/hb9mtn/hb9mtn_h-pole.html
It claims to have a great 80 meter radiation pattern, uses no radials and is only 32 feet tall.
I would presume I could make it half the size and get great results on 40m.
It can be center fed or off center fed.
Has anyone tried this antenna or simulated it in EZNEC?
Any thoughts on the H-pole?

tks

Dennis
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WN2C
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Posts: 467




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« Reply #1 on: April 03, 2013, 07:54:30 PM »

It looks similar to the Hentenna or even close to what Stepir is putting out now with the crank up vertical.

Rick  wn2c
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WB6BYU
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Posts: 13337




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« Reply #2 on: April 04, 2013, 10:21:00 AM »

Quote from: AE5EK

Has anyone tried this antenna or simulated it in EZNEC?



Clearly someone has modeled it in EZNEC, as, according to the article, that is
how the antenna was developed originally, and the source of the plots provided.
My only comment on that is that it would be interesting to compare the plots
provided with those over "high accuracy" ground rather than MININEC ground,
as the Summerfield-Norton algorithm does a better job of modeling the losses.

I'd also be interested in the wire losses and the feedpoint impedance, particularly
on 80m, where the feedline may radiate more than the antenna in practice.


Basically on 40m it is a half wave dipole with the ends bent around nearly back
to the feedpoint, giving a total length of 1/4 wavelength.  This lowers the
radiation resistance quite a bit.  By contrast, the CrankIR vertical uses a wide
top section so the far end doesn't drop quite as close to the feedpoint, which
improves efficiency somewhat.

I've modeled several similar designs as part of a project on shortened 160m
antennas, and, in spite of the low radiation resistance, they can be made to
work reasonably well.  I also modeled the "C" vertical.    In both cases the
current distribution on other bands certainly isn't optimum, but can be at
least usable.  (The C antenna also advertises itself as capable of multi-band
operation with a tuner, though it really works best as a single-band antenna.)

I wouldn't count on operation below 40m with this design, however.  Yes, it may
radiate somewhat:  I've made 80m contacts using the cord to my soldering gun
laying on my workbench, but I wouldn't consider that an effective antenna, either.

So if you want a good 40m antenna, I'd stay with the antenna is presently
dimensioned, where it uses about 1/2 wavelength of wire.
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KG4RUL
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Posts: 2735


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« Reply #3 on: April 04, 2013, 10:26:22 AM »

The thing to remember with EZNEC and other similar modeling programs is, they are based on assumptions about the performance of antennas excited with RF energy.  Yes, they are based on empirical data but, somewhere, you have to be stretching the assumptions too far.  The ONLY real performance measure is getting the test antenna on a range and performing real measurements.
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K4SAV
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Posts: 1847




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« Reply #4 on: April 04, 2013, 01:29:36 PM »

I looked back thru my old EZNEC files, and yes it is there, several versions, including his original file. 

The short summary is: stay away from the off-center fed version.  In that version, the feedline does most of the radiating, so the gain will depend on the feedline length and how it is routed.  A feedline near the ground will work like a dipole on the ground. 

The center fed version isn't too bad (if your reference is a typical radial-less vertical), except on 80 meters.  The SWR on 80 is huge and even open wire line will have a lot of loss.  Over average ground the gain on 3.5 MHz using 100 ft of Wireman 551 ladderline is about -11.7 dBi.  On 40M the gain increases to about -2.7 dBi.  On 20M, it's about -2.7 dBi.  On 15M, gain is about 0 dBi.  On 10M, gain is about 1.7 dBi.  All those numbers are with 100 ft of Wireman 551 ladderline.  You should be able to do a little better if you build your own low loss open wire line.

Jerry, K4SAV
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