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Re: Cheap Yagi Antennas for VHF/UHF: experiences?



K5OE@aol.com wrote:

> I recently built a 10-element version in "cross-Yagi" style with
> orthogonally oriented elements.  I used 1" PVC pipe and #10 AWG Cu
> wire.  Unlike Howard's though, I did not offset the elements--I
> arranged the perpendicular elements adjacent to each and brought
> each feedpoint down to a coaxial relay on the mast for polarity
> switching.  Howard's version is fixed RHCP.
> 
> The design is indeed broadbanded and easy to tune.  The "J" feed
> element is novel in a Yagi configuration, but works very well as a
> nice balance between the too-touchy folded dipole and the too-low-
> impedance dipole.  I spoke to Kent about the design at the time I
> was building it.  I modeled it in YagiMax and NEC4Win95 but got
> different results... thus contacted Kent to discuss.

Jerry:

Kent's originally designed this series of "cheap yagis" first to get a
good 50 ohm feedpoint impedance, and then he worked out the rest of
the elements for the other properties like gain, F/B, etc.  I wonder
if the design is flexible enough that he (or you, or someone else)
could re-do it so that the feedpoint of each part was 100 ohms.  That
way, you could combine the horizontal and vertical feeds (or more
likely, the / and \ diagonal feeds) without any additional impedance
transformation -- no 75 ohm quarter-wave transformers or 2-port power
divider, just relay selectable phasing lines for the different
polarities, right into a T connector (two 100 ohm antennas in parallel
= 50 ohms).  I'd love to see such a design and attempt to build it, if
it worked.  Seems like it would be in keeping with the KISS and keep
it cheap philosophy.  (Ok, once you add 4 coaxial relays to get 4
different polarities, the cost and complexity go up.  But hey, if you
were willing to settle for just a single, non-switchable circular
polarity, it really DOES stay cheap and simple!)

Just thinking out loud.  (I have a great desire to get started in
antenna modeling and design, but no time to begin the process now.
I've got so many pending projects right now that I'm sure I'll never
be bored for the rest of my life!)

73 de KB0ZEV
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