Five-Element, 2-Meter Yagi for $20


Jay P White:
From an old QST article you can convert a Radio Shack FM broadcast receiving antenna into a 2m yagi.

Do you need to drive this type of antenna with a balun or can the feedline coax go directly from the radio to the antenna?

I think it is basically a dipole being fed with un-balanced line (coax) so a balun would be necessary so I am looking for suggestions on making a simple balun maybe similar in complexity to "6-turns of RG-8 around a 6" plastic pipe" like you would for for a single band HF dipole.

Any suggestions?  Jay KA2UGZ

Dale Hunt:
That particular design uses a gamma match, so a balun
shouldn't be necessary.

Though I'm sure the antenna works OK, $20 seems rather
expensive for a 2m yagi.  Personally I'd build one of
these instead:

Jason White:
What you are describing is a common mode choke, or a 1:1 un-un (usually refered to as a balun anyway). The idea behind it is to prevent the coax from radiating and carrying RF back to the shack. There really isn't any impedence transformation going on. You can do the same thing with ferrite beads.

Since the antenna design you are looking at is gamma matched, the impedence at the feedpoint should be 50 ohms you won't need such a device. Still, I usually slip a few ferrite beads on the coax near the feedpoint and retain them with a zip tie.

Putting a choke balun on a VHF beam is almost always useful.  You don't want any feedline radiation if you can avoid it, because that ruins your pattern.  Choke baluns help keep noise from the shack from being conducted onto the antenna too.

A coaxial choke is fine.  


Larry J. Rolewic:
Also do a Google Search for "Cheap Yagis."  There was a series of articles in "CQ-VHF" magazine a few years ago for just that, and while they might not be the ultimate in design, they still were low $ and offered decent performance.  The advantage is they were direct coax ferd, without complex or difficult adjustments.  Materials for a 2 Meter Yagi should be a LOT less than $20, and still provide extra material for antannas on other bands.
    (The feed/driven element was similar to a "j-pole" on it's side, although the antennas could be used in horizontal OR vertical orientation) so that's the article(s) to look for.  Unfortunately, I only have the bookmark on another computer or I'd include it here.)


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