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Author Topic: Quick 2m beam question  (Read 1634 times)
KG5HFO
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Posts: 8




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« on: June 15, 2015, 01:28:17 PM »

Just built a 2m 5-element loop beam. I am a newly licensed ham and this was my first build, but the SWR looks great. I am having a curious issue though. And it may not be an issue at all, maybe just environment?
I live in a cookie-cutter neighborhood with a bunch of brick homes really close to each other. I have only been able to test simplex with my buddy about 17 miles away. Pointing right at him, he's about an s3 on my radio and he can barely hear me. Pointed 180* away from him he's full-scale and I'm an s7/s8. The beam isn't up in the attic yet, only tested in the back yard at about 8 feet. Is there something simple that I'm missing, did I construct the beam wrong, or do you think it's just a product of the environment? Thanks in advance! -Adam KG5HFO
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KG5HFO
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« Reply #1 on: June 15, 2015, 01:35:50 PM »

Also, I was able to hit a repeater 85 miles south of me full-quieting. The beam was pointed north. That's gotta be bounce? I wouldn't think the signal would be that strong off the tail. It is quiet off the sides, though. When I turned the beam 90* in either direction from my buddy, no signal at all.
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WB6BYU
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« Reply #2 on: June 15, 2015, 02:27:24 PM »

It might be bounce off the surrounding buildings - that isn't uncommon in a city.  How high
is the antenna above the nearby rooftops?

It could also be a dimensional error in building the antenna - a reflector turns into a director when
the frequency is low enough.  Can you point us to the design you used?
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KG5HFO
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« Reply #3 on: June 15, 2015, 02:39:37 PM »

The antenna is only at 8ft right now. Homes in the neighborhood are abour 20ft to the peak, about 8-10ft of brick (single story homes). I built "Don's 2 Meter Extrem Dream Beam" as seen on youtube. My buddy has been a ham for several years and has built tons of 2m and 70cm antennas. Said it looks fine, and the swr is 1.3:1 on 144, 1.0:1 at 146, and 1.3:1 at 148. Exactly where I want it. Also usable on the MURS freqs and some portions of 70cm. Just looking for other opinions. Trying to figure out how to post a picture from my computer.

Quickly, here are the dimensions between each u-bend on either side of the element. The bends are approx 1-1/2" each:
Ref: 82-1/2"
DE: 78-5/8"
D1: 74"
D2: 72"
D3: 70"
« Last Edit: June 15, 2015, 02:55:14 PM by KG5HFO » Logged
KG5HFO
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Posts: 8




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« Reply #4 on: June 15, 2015, 03:00:55 PM »

https://flic.kr/p/uHfQPX

That's as best as I can figure out how to get an image up. Sorry. Hopefully that gives you an idea of the antenna and the surrounding environment.
« Last Edit: June 15, 2015, 03:06:46 PM by KG5HFO » Logged
WB3BEL
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Posts: 149




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« Reply #5 on: June 16, 2015, 06:12:56 AM »

I can see a few things from your post that look suspicious.

I looked at the build diagram on this site:

http://www.hamuniverse.com/ae5un2mextremebeamQuadantenna2.pdf

The loop dimensions you posted are very different from what is on this diagram?  Maybe you built a different antenna?
      Yours    AE5UN's
Ref: 82-1/2"  84"   (This is the back of the antenna)
DE: 78-5/8"   80-3/4"
D1: 74"         75-1/8"
D2: 72"         74-1/8"
D3: 70"         73"  (This is the front of the antenna)

AE5UN's diagram has these spacings between the elements. 
Ref-DE = 14.5"
DE-D1 = 9"
D1-D2 = 12"
D2-D3 = 18"
It's hard to tell from your flickr picture but you should double check the element spacings and position on the boom.

I think that using the nut and bolt to connect the ends of the element loops is a very poor idea.  It leads to uncertainty on the element length.  Why did he not put the total loop length and overlap the ends and solder?  That would be much more precise.  This diagram does not put details on the bends.  Also the bolt is likely to lead to corrosion and poor connections.  Probably the loop lengths will need to be modified to include some extra length (~1") to substitute for the bolt.

The other problem with this design is that the coaxial cable runs too close to the elements and is in the same plane as the polarization (vertical).  This will distort the pattern.  The coaxial cable should be dressed along the DE spreader to the boom,  run down the boom past the Ref  (the boom should be lengthened by 2 ft past the Ref).  Make a loop at the the far end of the boom past the ref and route it down the mast.  This keeps the vertical run of the coax behind the antenna.  Vertically polarized antennas should have the cable to the rear of the antenna.

It could be that this antenna is not a very good design in other ways.  I did not take the time to analyze it.

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WB3BEL
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« Reply #6 on: June 16, 2015, 06:42:23 AM »

Yes.  This is what I wondered when I read your post.  

D3 is the front of the antenna.  Point it at the station you wish to work.

In your flickr picture the antenna is pointed over the fence.  The back of the antenna points at the ladder.
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KG5HFO
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« Reply #7 on: June 16, 2015, 11:35:21 PM »

Yup, I'll chalk this one up to being a newbie. Well, you live and learn. I always thought the element facing your target being called a "reflector" and the ones after the driven element being called "directors" was strange. Haha. My apologies and thanks for setting me straight. One thing I love about this hobby above most others is the willingness of people to help out a new guy no matter how dumb the question Smiley
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