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Author Topic: First attempt at a phased wire array antenna  (Read 1419 times)
WD4ELG
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Posts: 183




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« Reply #15 on: December 02, 2017, 05:03:10 PM »

I decided to start with a simple phasing approach, described in ON4UN's book (5th ed), where John lists out a close-spaced phased dipole (1/8 wave separation), fed 180 degrees out of phase, with 1/4 wave coax to one dipole and 3/4 wave coax to the other dipole.  This current forcing simplifies the task of getting the right currents to the dipoles without a complex phasing network.  The impedance at the junction won't be 50 ohms (I will need to measure it), but I can easily put a spare remote coupler at that point so the coax loss due to SWR between that junction and the shack is minimized.

First dipole is up at 32 feet and pruned for 3505 kHz.  Second dipole will go up early in the week. 

I decided to tinker with the first dipole and see what results I get, 9 PM Friday night local.  Called CQ with my FT817ND on 5 watts just for kicks.  Nobody answered.  Went to FT8 and worked a bunch of US stations with 1 watt.  Went back to CW and 5 watts, heard HA8RM calling CQ so I replied.  Got a 569 response to my "worthless low dipole and peanut power."  Now it makes me wonder if I should even continue with the phasing experiment!  Well, at least I know the one antenna must be doing OK and I am being heard with the first dipole.
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WE6C
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Posts: 26




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« Reply #16 on: December 05, 2017, 09:57:47 AM »

An 8JK after W8JK is a better performer at low heights according to many.

I had one up for 75 at about 35-40' aimed at Europe and the South Pacific that did far better than a pair of 1/4 wave phased verticals hanging from tree branches when conditions were favorable.
It was far lower noise than the verticals or an inverted V at 90' yet signals were stronger in the favored directions and elevation angles.

A plus is multiband use with gain.

Then I moved here and had no simple way to support it.

Here two of many articles on the 8JK worth reading.

http://www.bvarc.org/Tech/CompactW8JKBeam-K5LJ.pdf

http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/radcom/1990/09/page31c/index.html

Carl

Carl, Was your 8JK with elements side by side or one above the other?
Bob  WE6C
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KM1H
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Posts: 2617




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« Reply #17 on: December 05, 2017, 12:04:29 PM »

In line as in a 2 el yagi or HB9CV, etc.
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KZ4USA
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Posts: 298




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« Reply #18 on: December 05, 2017, 01:58:59 PM »

Inverted L might be better and wonder if you could phase two of them in line.
« Last Edit: December 05, 2017, 02:01:30 PM by KZ4USA » Logged
WD4ELG
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Posts: 183




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« Reply #19 on: December 05, 2017, 09:53:32 PM »

KZ4USA, I do have an inverted L for 160 that I use on 80 with a remote coupler.  It's about 1/2 wave on 80 so the ground losses are probably less than 160 due to higher impedance.  I will do some comparison tests when the phasing cables arrive for the dipole array.
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WD4ELG
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Posts: 183




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« Reply #20 on: December 08, 2017, 05:33:26 PM »

Phasing cables ready for installation...but it is snowing and sleeting nasty out.  I know, "MAN UP."  It's 8:30 PM local, I cleaned the snow off the porch and deck (twice), walked the four dogs, did a bunch of chores around the house.  It can wait until tomorrow.  It's just a hobby.  It's just a hobby.

...
...

Let me check and see if it stopped snowing and sleeting yet...
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W1VT
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Posts: 2527




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« Reply #21 on: December 08, 2017, 05:44:15 PM »

Just remember that if you drop any small hardware in the snow you won't be able to find it until the snow melts.
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WD4ELG
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Posts: 183




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« Reply #22 on: Yesterday at 09:30:44 PM »

13 DEC 0500 UTC update:

Phasing cables are hooked up.  A a 1:2 UN-UN is in place to get a decent match right after the splitter where the feedline and phasing cables meet.

I now have two half-wave dipoles, 1/8 wave high, separated by 1/8 wavelength, 180 degrees out of phase.  The cables are fed using 1/4 and 3/4 length coax (using the current-forcing property of 1/4 wave feedlines).  This should give me an oval pattern, broadside to the array, with a null overhead.  (See ON4UN Low Band DXing, page 12-3, Figures 12-2 through 12-4.  However, the height of the phased dipoles is not 1/3 wave but rather 1/8 wave.  With the antennas closer to ground, I would expect lower impedance...a higher radiation angle maximum...and the null overhead to be "nullified."

This pattern is verified by my EZNEC 5 simulations using high accuracy ground.  (I also learned that EZNEC 5 uses the less powerful, less accurate NEC-2 calculation engine rather than the NEC-4 calculation engine.  Well, close enough for government work, as the saying goes).

So how does the dipole array REALLY work?  I am comparing it to an Inverted L that is 1/2 wave long in 80 meters: 90 foot vertical, 42 foot horizontal, with 20 radials over average clay soil. 

My transmitter is an FT817ND running WSPR 1.8, WaveNode WN-2 wattmeter confirming 500 milliwatts. 

I am analyzing the parameter "DX 10" on the SotaBeams website.  I can see an improvement in the DX10 metric when I swap from the phased dipoles to the inverted L.  Which makes sense, at first glance.  However, the DX10 figure of merit is a measure of weighted SNR and distance.  Since the inverted L is omni-directional, it is sending low angle radiation in all directions. 

A more accurate comparison will be broadside to the array.  Since the array is aligned E/W, the lobes will point N/S.  Anything outside of 315<->045 on the phased dipole array will be attenuated and the inverted L will do better.  It's in this 315<->045 cone that I am interested, and that's why I put the thing up to get better signal to EU.

More data collection is needed, with specific measurements made within the 3 dB lobe pattern of the array and WSPR stations in that range of 315<->045. 

Also...without a measuring device, I am assuming proper phasing is in place.  The impediment to this assumption: other objects in the near-field (within 1/2 wave of the dipole array I have a four-square receive array, the inverted L, a 5-band hex beam and a 5 element yagi for 6 meters.)  Although at higher elevations than the phased dipoles, the hex beam and 6 meter yagi may impact the radiation pattern.   But they can also impact the inverted L, so the overall effect may be the same for both antennas under test.

Next steps are to conduct extensive WSPR data collection.

Based upon very preliminary data from WSPR SNR readings, it seems that the inverted L is 3 dB better in all directions, except for distances under 500 miles (which aligns with the overhead lobe no longer nulled).  But that does not imply the phased dipoles have no DX value.  I am seeing consistent reception of my 500 mW from the phased dipoles at numerous EU stations.  I need to do some RBN measurements and work some DX (CW only, of course, since the phasing cables are cut for the low end of the band).

Additional questions for me to investigate:

Since the inverted L has a remote coupler at the base (CG-3000 model), how will the losses in that unit impact the inverted L at higher power (500W max) when trying to break a pileup?
Is the 1:2 un-un for the phased dipoles (Balun Designs manuf), a lossy unit at higher power when trying to break a pileup?
Both the Inverted L and the phased dipoles are fed with 300 feet of LMR-400.  But I am using RG8X for the phasing lines due to the lighter weight.  Will this be a factor at 500 W?

Future research: can I separate the dipoles further and experiment with more complex phasing systems?  Is it worth the effort?  Certainly, this arrangement can work DX (already proved that, see earlier post).  And I have a separate HiZ receive array in use anyway, so the dipole pickup of noise due to low height is ignored.  If I did not have the inverted L, would this phased array be enough to get me DXCC on 80 CW?  What about if I tried barefoot with 100 watts?

All this practical research/investigation brings back delightful memories on the antenna test range at Georgia Tech when I was getting my MSEE a quarter century ago (wow, time really passes by quickly!) 

Thanks for the comments, feedback and help.
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