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



Hmm so what you are saying is if you enter the models into YagiMax and make 
a note of the feed impedance, then if you scale the design to  new numbers 
of elements, the J-feed should work as advertised-- assuming that YagiMax 
still says the feed impedance is close to the original 17 Ohms?!?  I 
suspected this would work, maybe I'll have to try it... Hmm..

One thing I've wanted to try (and yes I know this defeats the "cheap yagi" 
idea a bit) is scaling the designs so they could be built on a conductive 
boom (insulating the J-feed, of course).  Might have to try that as well.

Thanks for the info..

Fred W0FMS
>From: K5OE@aol.com
>To: <fspinner@hotmail.com>, <fant@thesteeles.net>, <amsat-bb@AMSAT.Org>
>Subject: Re: [amsat-bb] Cheap Yagi Antennas for VHF/UHF: experiences?
>Date: Wed, 20 Feb 2002 10:23:50 EST
>
>Fred,
>
> > Send an e-mail to Kent Britian and ask him.  Unfortuately, it is simple 
>if
> > you are the guy who designed the originals, but if I remember correctly, 
>he
> > used YagiMax to design the rough antennas and then used the YagiMax'ed
> > models in NEC to optimise.  I think K5OE said once that the J-matched
> > elements designed to be fed, if they were normal straight elements, with
> > like, 17 ohms impedance.  (3:1 impedance transform ratio with the "J"
> > match).  But don't hold me to that.
> >
> > So the simple answer is, unless you already are fairly good at modeling
> > antennas, there isn't a simple answer.
>
>Correct on all points.  My attempts at modeling the J-feed in NEC4 did not 
>work out well, but the YagiMax models do work as advertised (I also do the 
>same thing with folded-dipole designs, using 12.5 Ohms as the feed 
>impedance).
>73,
>Jerry, K5OE
>
>----
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>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org




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