Re: [amsat-bb] Cheap Yagi Antennas for VHF/UHF: experiences?

[joseph Murray <k0vty@xxxxxxxx>]

Hi All

If I might suggest, if there is a re-design of this antenna ( AMSAT 435
mHz  ) that consideration be given to higher gain versus lower front to
back ratio.     My reasoning is only valid if the antenna is used for
satellite 70 cm up link antenna .
If the antenna is to be used for satellite 70 cm receive then the
original higher front to back still applies.

73's  Joe K0VTY
=====================
On Thu, 14 Feb 2002 21:14:27 -0600 "John P. Toscano"
<tosca005@tc.umn.edu> writes:
> 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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