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Author Topic: Pair of Hex Beams, 30 feet apart, phased, thoughts?  (Read 1190 times)
KU7I
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Posts: 122




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« on: September 05, 2012, 02:45:47 PM »

Considering a pair of 5 band hex beams on separate push up poles, 30 ft apart, phased. One push up pole is 30ft and the other is 42 ft and they are 30 ft apart. Not only would I get horizontal  separation by 30ft but would have a bit of offset in elevation also. I am wondering if I could phase these? Each one would be on its own rotor. 30 ft horizontal spacing should give separation for 20-17-15. Your thoughts? Lane Ku7i/JH1JCM
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WX7G
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« Reply #1 on: September 05, 2012, 03:03:04 PM »

This question can be answered with a NEC simulation. Anyone want to run one for the OM?
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WB6BYU
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« Reply #2 on: September 05, 2012, 05:10:36 PM »

The phasing will change as you rotate them.  That's not impossible to solve, it just
takes a bit more work.  You could probably do it with switched line sections, possibly
binary lengths, and would have to be able to accommodate +/- 30 feet.  The big
question then is how small of an increment do you need.

You could do it with discrete phase shift networks, but then you need to readjust
it for each band.  I'd guess that the line sections would work well enough on all
bands so you don't need a separate set for each.
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K3VAT
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« Reply #3 on: September 05, 2012, 05:18:29 PM »

Considering a pair of 5 band hex beams on separate push up poles, 30 ft apart, phased. One push up pole is 30ft and the other is 42 ft and they are 30 ft apart. Not only would I get horizontal  separation by 30ft but would have a bit of offset in elevation also. I am wondering if I could phase these? Each one would be on its own rotor. 30 ft horizontal spacing should give separation for 20-17-15. Your thoughts? Lane Ku7i/JH1JCM

IMHO, this is very difficult (maintaining proper phase as both antennas rotate the entire 360 degrees across the e plane) and would have limited benefit (the distance between the two antennas [30'] is optimum for only one, perhaps two bands [out of the 5] and the antennas are at substantially different heights [12'].)

Modelling could probably show you a few cases that may work (maybe positioning both antennas broadside to your target DX for a few dB gain), but how are you going to maintain the correct phase relationship when you move the antenna to a new azimuth heading?  Mutual coupling between the antennas is a continuous variable when one or two antennas rotate.

Searching around this forum and generally on the web I haven't found any station using this type of antenna system.

You'd have a far more workable system if you were to vertically stack the antennas.

(Ops, composed during WB6BYU's posting).

73, Rich, K3VAT
« Last Edit: September 05, 2012, 05:35:07 PM by K3VAT » Logged
KU7I
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« Reply #4 on: September 05, 2012, 06:58:07 PM »

Thanks Rich, I am looking at vertical stacking.

Lane
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K0ZN
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« Reply #5 on: September 05, 2012, 07:17:28 PM »

 Short, real world answer:  NO.  

 Vertical stacking is the only practical answer.  If you are working/designing a fixed, point-to-point circuit, I suppose you could work out a horizontally phased system, but as soon as you start rotating them, the phasing or method of maintaining correct phasing gets quite complex.

73,  K0ZN
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WB6BYU
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« Reply #6 on: September 05, 2012, 08:03:59 PM »

A system of this sort was described by W6KPC as a "Line Array of Rotary
Antennas in Echelon (LARAE)" in the ARRL Antenna Compendium, volume 1.
He used three 4-element 80m yagis spaced 1 wavelength apart in a line,
with phasing sections to maintain proper phase among them as they
were rotated.  The math is given in the article, and is basically just
simple trig, though a bit complicated by having to consider all three
dimensions for directions other than broadside.  He used 1/16th
wavelength sections switched in or out to provide the phasing.

For multi-band use, you'll have to design the phasing steps for the
highest frequency:  1/16th wavelength on 10m would be 2 feet long,
and you'd need at least +/- 30 feet to match your spacing. 

Would it add a lot of gain?  Hard to say:  mixing antennas at different
heights can be problematic because that means half you power is
going to an antenna that doesn't have as good of a vertical angle
of radiation.

But the details aren't difficult to work out if you are interested.
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W4OP
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« Reply #7 on: September 05, 2012, 08:32:13 PM »

Thanks Rich, I am looking at vertical stacking.

Lane

I do not own a Hexbeam but isn't the center post part of the feed system? I would think this would complicate placing any antenna above a Hexbeam, or at the very least make vertical stacking a lot more difficult than say  classic Yagis or quads.

Dale W4OP
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