Is this all for gamma matched driven element or a direct fed driven element or does it matter??
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2 Element Yagi
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See the above article about boom length and SWR when direct feeding the driven element with coax.
It's worth the effort if you have room to turn them.
73
Jeff
Thanks for the help. I'm making a new beam out of my old 4 element that came down many years ago in a north easter blow.
Buddy of mine in Oklahoma has been making 2 element yagi and they work great. Built one with a bed rail for the boom and golf ball retrievers for the elements. Works great for him.
A moxon is a fine beam. A local across the line in BC has one that talks all over the place. We're 12 miles apart and when on the vertical here when he's pointed at me on the flat side I hear him at about half the signal as when he's on his vertical. When he points it SE or SW I can barely hear him. Back and side rejection is great.
Question:
With the direct fed 2 element I'm building, What if any benefit would there be to insulating the reflector from the boom as opposed to attaching the reflector directly to the boom??
Attaching it to the boom adds a DC ground which prevents static electricity from building up and distorting the pattern. If you use a gamma match, you can also attach the driven element to the boom too.
There are many people that have destroyed their antenna analyzers by connecting them to coax cables attached to antennas that lack DC grounding. The antenna will charge the coax (when the other end is not attached to a radio ~ it acts like a capacitor storing the charge the antenna picks up) and if that is connected to an antenna analyzer without first shorting the coax to dissipate this charge, it can easily be game over for the analyzer/VNA. That is one reason why I prefer antennas with DC ground on the elements. It is not that I am careless, it is just another safeguard.
If you go with a moxon, those are typically designed to be fed with 50Ω directly so a gamma match would not work on the driven element. However, you can ground the reflector, and as long as you are aware of the risk to your analyzer with the ungrounded driven, it will work perfectly. This site has a great moxon calculator you can download.
Welp, I finished the beam today...sorta.
2 element driven with a reflector and a 1:1, double toroid 240-43 common mode choke with 1" to 7/8" element taper. reflector is bonded to the boom.
It worked out pretty good with a 1.05 vswr, +3 reactance and 52 ohms. I'm gonna work on it a bit more...maybe lengthen the boom a bit more to get closer to 50 ohms and element length for zero reactance. No matching network, direct fed.
The boom element separation is 7' 10". I lengthened the boom once 1/4 inch and the impedance dropped from 55 ohms to where it is now, 52 ohms. vswr and reactance didn't change. It'll be interesting to see what the band width and beam width will be with the long boom.
2 element driven with a reflector and a 1:1, double toroid 240-43 common mode choke with 1" to 7/8" element taper. reflector is bonded to the boom.
It worked out pretty good with a 1.05 vswr, +3 reactance and 52 ohms. I'm gonna work on it a bit more...maybe lengthen the boom a bit more to get closer to 50 ohms and element length for zero reactance. No matching network, direct fed.
The boom element separation is 7' 10". I lengthened the boom once 1/4 inch and the impedance dropped from 55 ohms to where it is now, 52 ohms. vswr and reactance didn't change. It'll be interesting to see what the band width and beam width will be with the long boom.
Shadetree Mechanic
Delaware Base Station 808
Thanks for the link to the Moxgen, I am going to make one for my GMRS radio just to play around with. Will probably use coat hanger wire.
