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Author Topic: 2 meter beams  (Read 639 times)
KE5LGG
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« on: June 02, 2008, 05:41:34 AM »

I have 4 cushcraft 2 meter 11 element beams. So that i would have the ability to work vertical and horizontal stations, would i be better off: A) turning two horizontal and two vertical and switching between the two, or B) turning all 4 diaginal?

Which would be my best choice?

Thanks

KE5LGG
Cody
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KB9CRY
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« Reply #1 on: June 02, 2008, 05:55:27 AM »

A
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WA3SKN
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« Reply #2 on: June 02, 2008, 06:32:59 AM »

"A"... just from the mounting practicality!
Since they are "narrow-banded" in nature, tune the vertical ones for the high end of 2 meters where the FM activity is... and the horizontal ones tune for the low end, where the USB/CW activity is.
73s.

-Mike.
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G8UBJ
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« Reply #3 on: June 02, 2008, 06:33:04 AM »

my money is on A

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AA4PB
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« Reply #4 on: June 02, 2008, 06:41:01 AM »

Option A.  The theoretical loss for cross polarization is about 20dB and that's a lot. Turning them 45 degrees will reduce that loss but I'll bet its still quite a bit, certainly more than the 3dB gain you get from doubling the number of beams in the array. Bottom line is you'll get more total gain by using half the total elements and matching the polarization properly.

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WB2WIK
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« Reply #5 on: June 02, 2008, 08:43:24 AM »

First, I'd inspect and clean the beams, and make sure the gamma match components are good with very clean and tight connections.

The "weak link" in the 11 element CC 2m beams has always been the "Redi-match" (gamma match), which is not a great implementation.

I would tune them each individually for 146.000 MHz, temporarily installing each beam about 10' above ground on a wooden pole supported by a tripod or equivalent.  "Tune up" should be with each beam installed horizontally, to keep the transmission line out of the field of the beam.

Then, I'd make or buy a 4-port power divider to split the four beams and reach each beam okay when they're stacked in an "H-frame" that is 9'6" wide by 9'6" high and made of all extruded aluminum or carbon steel masting (10' sections).

Install all four at a 45 degree tilt, all tilting the same way.

Results: About -3 dB from using pure vertical or pure horizontal when working stations of those standard polarizations; however, this is still exactly as good as using just two horizontally or just two vertically, and the advantage is they're much easier to install this way.  Installing vertically polarized beams properly involves a long cross-boom for support, anyway; and installing two horizontally polarized beams properly involves a long mast.  By combining them all, you occupy no more space than the separate H/V equivalents but end up with a sturdier frame that self-supports in all directions when rigidly clamped.

The -3 dB is easily modeled and measured; we determined this empirically many years before modeling software became available, at the U.S.A.F. Rome Air Development Center in NY, where there was a need for using both vertical and horizontal polarization in the 136 MHz band and years of experiments resulted in the "tilted yagi" approach, measured to be 3 dB down from either H or V, repeatedly, irrespective of distance to target (all tropo).

One great advantage of this approach is using a single feedline for everything, and of course the array is very well balanced mechanically, making it stronger than some other configurations.

The only drawback really is if you ever happen to stumble across another station doing the same thing but with tilted yagis of the "opposite tilt," in which case you probably won't even hear him.  But the likelihood of that is very small.

WB2WIK/6
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N9DG
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« Reply #6 on: June 02, 2008, 08:57:36 AM »

WB2WIK: "Install all four at a 45 degree tilt, all tilting the same way."

So then how does the polarization match up with the other station that you are working if they have also tilted their beams with the same 45 degree tilt?Huh
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WB2WIK
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« Reply #7 on: June 02, 2008, 09:13:02 AM »

N9DG: It doesn't.  But it's so rare that anybody does this, it shouldn't matter.

In 43 years of operating 2m, I've only found maybe three stations in the country using tilted yagis, and I was one of them.

Odds of running across people doing this are very slim.

It works very well when working stations using either vertical or horizontal polarization, or RHCP or LHCP (doesn't matter).

WB2WIK/6
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N9DG
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« Reply #8 on: June 02, 2008, 10:56:24 AM »

WB2WIK: "Odds of running across people doing this are very slim."

Perhaps in the past. But now that this topic about covering both polarities, and the 45 degree "solution" for it has been mentioned several times in the last few months now, there will be more who will be doing it. That's why when this came up the last time I suggested that the original poster just do it, - but don't tell anyone else about it Wink...

I haven't studied it closely but in this case the original poster could achieve the same thing with the 4 antennas by pairing 2 together vertically, and two horizontally. He'll still take the same ~3dB hit but solve the 45 to 45 problem. He would likely need to space the vertical pair and horizontal pair extra far appart to avoid undesirable interaction... Just an idea.
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N6AJR
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« Reply #9 on: June 02, 2008, 11:23:19 AM »

I find most long distance work on 2 meters is done with a horizontal polerized antennas. most of the FM stuff is set up as a verticle.  so I would mount all 4 as horizontal, on a nice rotor, and put a cheep verticle on top.  You can build a 1 in 4 out or buy a cable setup from cushcraft. run 2 lines, on to the vert and one to the 4 antennas in sync
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K2DC
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« Reply #10 on: June 02, 2008, 12:19:38 PM »

Cody,

I agree with Steve, WB2WIK. I used to have up a 13 element 2M and 19 element 440 beam with El over Az rotors. I was interested in playing with the stallites (before all the good ones went dark) as well as other things. FM is all vertical, SSB/CW is all horizontal, and the satellites are all CP. I mounted both antennas at 45 degrees, knowing I had plenty of gain, so I gave up 3 dB to all of them and still worked them all.

Yes, it's possible to run across somebody with beams at -45 degrees. But again, I agree with Steve. Most people mount them H or V, very few at 45 degrees in either direction. If on a rare occaision you do run across that situation, you may not hear them at all and you'll never know the difference. If you put up a good system and then worry about everything you can't hear, you'll drive youself nuts anyway.

GL and 73,

Don, K2DC
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WB2WIK
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« Reply #11 on: June 02, 2008, 01:45:03 PM »

You'll never run into anyone on FM/repeaters doing this, really: Mobiles use vertical whips and repeaters use vertical omnidirectional antennas, and that's about all you need to work on FM, usually.

On SSB, it's certainly *possible* to run into somebody using angular polarization, and it might be incompatible, but I must say that in four decades on 2m SSB it hasn't happened to me yet.

99% of everybody on SSB (and CW and WSJT) are using horizontal or circular polarization, and the angular tilt polarization is very compatible with either.

WB2WIK/6
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