[SEDXC] Mystery 6m Beam

[aa4lr at mac.com]

Back in July of 2021, I asked members of this reflector how best to work Europeans on 6m, one piece of advice I received was to use an antenna with more gain than my Cushcraft A50-3S. I was told I need five or six elements for these marginal paths. 

Leaving the recent Dalton, GA hamfest, I stopped by a tail gain where someone had a trailer load of antenna stuff. I could see a Cushcraft tribander, a Hy-Gain tribander, house brackets, guy brackets, feed lines, a gin pole, etc. I asked if they had any 6m beams.

The owner wasn't present, so his kid called him on a digital walkie-talkie. He said he had a 5-element Cushcraft 6m beam. By the time he made it back to the trailer, we pulled it out, and he changed his tune, he said it was a 6-element Hy-Gain beam. The gamma match on the driven element was evident.

I negotiated him down to 63% of his asking price, and walked away with the antenna bundle for $125. Sweet.

As soon as I got home, I went looking for Hy-Gain six-element 6m beams. I found manuals for models 66B and VB-66DX. The VB-66DX appears to be a hardware-update of the 66B design. These antennas are also fed with a beta-match, not a gamma-match. What I bought is NOT a Hy-Gain antenna.

I cut the antenna bundle apart and spread the pieces out on the deck. What I found was surprising:
    • REF - 3/4" Al - 9' 9" - 117"
    • DE - 3/4" Al - 9' 2" - 110" (Gamma match)
    • D1 - 3/4" Al - 8' 9" - 105"
    • D2 - 3/4" Al - 8' 8" - 104"
    • D3 - 3/4" Al - 8' 7" - 103"
    • Misc - 1/2" Al - 50" - Swaged to 5/8" last 6" (2) - Hy-Gain bracket adds 1 1/2" - 101 1/2" total
    • Boom - 1 1/4" Al totalling 24 feet in three sections with 1" thicker wall inner tubing

First five elements mount with a single 1 3/4" U-bolt and saddle in the center. The Misc segments could mount in a single Hy-Gain bracket, giving a total element length of 101 1/2" -- which might be a forth director.

Gamma match is a total of 16" 1/2", most of which is a 1/4" Aluminum rod. The shorting bar is at 14 1/2". The first 1 1/2" is a 1/2" Al tube flattened at one end for a screw. The open end hid a disc ceramic capacitor that sadly I broke in transit. Looks like a 3-6 kV capacitor, value unknown.

The boom is a piece of work. There are three 1 1/4" Al sections: 75 3/4", 144", 68". The 68" section has a 156" piece of 1"Al tubing with a ticker wall as reinforcement. It is mounted asymmetrically, so more of the end extends into the 144" piece than the 75 3/4" piece. There is no boom to mast bracket.

Clearly, these parts do not belong to a Hy-Gain nor a Cushcraft 6m beam. First off, no commercial 6m beam ships with single-tubing size elements. They all use a taper schedule. There are two good reasons for this. 1) It makes the antenna adjustable. 2) they can ship sections shorter than 7 feet, which allows the package to go UPS, 

These parts are a collection different ideas. The U-bolt mounting is Cushcraft-style, but the boom size is too small for a Cushcraft. The boom is 24 feet long, but it is clearly not a Hy-Gain. The boom is way too small, since Hy-Gain used a 2" boom. Plus, it apparently had a truss (now broken), probably because the    for the 24 foot length.

What I appear to have is a collection of parts used to cobble together a poor imitation of something like the Hy-Gain 66B / VB-66DX. Not at all what the guy at the hamfest told me.

There's plenty here to put together a solid five element beam on a 12 to 18 foot boom. The elements are already cut. The hard question is: how far should they be spaced? Once I know what the right spacing is, I would then know how much boom I need. 

The broken gamma match is annoying, but fixable. Once I know where to place the elements….

Anyone have any hints they could offer? Any ideas to adapt the elements I already have to a workable 6m Yagi?