[VHFcontesting] Portable 50 MHz beam antennas

[nosigma at aol.com]

Mark,
I modified a 6 element beam to break down in a few minutes and go back together accurately and almost as fast with no tools required.  Some of what I did might be useful to you.  

I now wish I had pics on the qrz page of this. I can take and send pics later if desired.

The elements are each 3 piece with the outers slipping inside the center. With the beam assembled and tuned with a spectrum analyzer I wrapped electricl tape on the outer elements so one edge of the tape is against the inner element.  This controls the depth and avoids measuring on reassembly.  

Next I slit the ends of the larger inner elements so there were 4 slits about an inch long in each end.  At the auto parts store I picked up hose clamps with large plastic wing nuts.  I use these to clamp down on the inner element ends and secure the outers.  It wont work with just two slits, you need 4 or the force required will snap the plastic wings off.

Next I punched small holes in the plastic end  caps.  Using a 12 foot leader of mechanics wire I threaded an elastic  chord through the full length of the element.  Tie the ends off around a short length if black plastic zip tie.  Make sure the elastic is under tension when the element is assembled.  Make sure there is enough stretch so you can pull the elements out.  Snug down the claps after pulling out the outer elements so you dont loose the clamps.

With the elements out lay them over the top of the inner element.  Secure the outers to the inner with a wrap of double sided velcro on either side of the boom.

If your boom uses saddles and through bolts to secure the inner element to the boom your in luck.  Loosen the center bolts in all inner elements.  Rotate ALL of them until they lay as parralel to the boom as possible.  Mark the saddles either side of the center element one one saddle.  Remove the saddle and put a shallow notch in it so the inner element has a shallow detent to rest in.

Reassemble, then Mark and notch the next saddle.  Reassemble and continue until they are all notched.  When you are done the package should a foot or two wide and anout 3 feet longer than the boom.  Secure the packaged elements with a couple more strips of double sided velcro.

The feed will take some thought.  I flipped mine (gamma match) and made new brackets so it sat above the driven element which is above the boom and sat above the driven element the same distance as it sat below it when under the boom.

When your all done set it up and retune it with an analyzer.  There will be small changes due to the clamps and feed changes.

Another thing I did to save weight, important since your packing it in, was to use much smaller boom tubing.  I run 550 chord from one end up to a stand off for h pol or to the center element for vpol. This adds a huge amount of strength, more than what you loose if you do it right.

Gotta go.  Dinner out tonight.

73
John
KM4KMU


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On Wednesday, February 14, 2018 Mark Spencer <mark at alignedsolutions.com> wrote:
Hi:

I finally took delivery of a suitable LiPo battery to facilitate "back pack portable" operation at the 50 to 100 watt level. If any of my Canadian colleagues are interested I can provide the contact details for a Canadian distributor.

At this point I'm planning on simply taking my 50 MHz three element beam apart and re assembling it on site. In my view the beam I have isn't really intended for that type of use and I'm curious if anyone knows of any suppliers for small 50 MHz beams that break down and re assemble quickly and easily. Google searching on my part didn't turn up anything that is currently in production. 

I'm hoping to shift my focus a bit this year and actually reach the true summit of at least one local mountain (vs simply driving most of the way up via logging roads.) Having this ability would also have been useful earlier this year when I had to abort my CO81 visit during the sept contest. In hindsight I suspect I could have activated the grid for a few hours on foot.

73

Mark S

Aligned Solutions Co.
mark at alignedsolutions.com
604 762 4099
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