[NLRS] Tuning 222 yagi [solved]

[Mike A. King - KM0T]

Brent, glad you got er going.  Hope to work you in the contest!

73

Mike - KM0T en13vc

----- Original Message ----- 
From: "Brent Casavant" <b.j.casavant@ieee.org>
To: "Northern Lights Radio Society" <nlrs@mailman.qth.net>
Sent: Friday, June 13, 2003 9:59 AM
Subject: Re: [NLRS] Tuning 222 yagi [solved]


> Hello again,
> 
> Well, it's probably bad form to respond to your own posting, but
> I'm fairly excited.  I got the beam tuned!
> 
> I seem to have stumbled upon an unorthodox tuning method.  Well,
> unorthodox in that I haven't seen this described anywhere before,
> but it's worked for me with two seperate Yagis (222 and 70cm).
> 
> I use a T-match on my driven elements because that's what I know
> how to build, and I'm getting good enough at it that I even like
> how it turns out cosmetically.  Also, this seems to be what is
> detailed in the K1FO designs in the Antenna Book.  I build my
> T-match out of an appropriate gauge wire (12 for 70cm, 10 for 222)
> and a hand-bent piece of aluminum to serve as the strap between
> the matching section and the driven element.  I don't use any
> capacitors in this design, though I understand that some people
> get better tuning results if they insert capacitors at various
> points in the matching section.
> 
> To tune, I start with the matching section cut fairly long (just
> a few centimeters short of the driven element).  I then move
> the connecting straps around until I minimize the SWR.  Usually
> the SWR at this point can't be driven below about 2:1 or higher.
> Also, the straps almost invariably end up very near the center
> of the driven element (i.e. near the boom).
> 
> Then I begin snipping off sections at the end of the matching
> section.  I start with about 2-2.5 centimeters at a time, and
> reduce this amount as the antenna begins getting a better SWR.
> I only snip off wire from one of the two ends of the T-match at
> a time.  Usually this starts dropping the SWR fairly rapidly,
> and it's not at all hard to get the SWR below 2:1.  After any
> significant drop in SWR via clipping, I take a bit of time to
> readjust the straps to minimize SWR.  If I'm still not happy
> with the SWR at that point, I resume some of the snipping.
> I seem to be able to eventually drive the SWR at the frequency
> of interest down below 1.5:1 (usually in the neighborhood
> of 1.3:1), and have adequate SWR bandwidth to work the rest
> of the band below 2:1.
> 
> The whole process usually takes less than a half hour, and
> gives fairly good results.  One outstanding problem I have
> is that the SWR doesn't match up as well as I'd like across
> the entire band, but I suspect that's more due to the design
> of the Yagi (designed via computer with QuickYagi) than a
> problem with the matching system.
> 
> So, I don't know if any of this is helpful, or just stunningly
> obvious and trivial.  But I do know that it seems to work, is
> reproducable, and makes a fairly quick job out of a problem that
> otherwise seems to take days and results in the use of words
> my mother doesn't know (and I don't mean "capacitance" :).
> 
> If anyone has any comments on this tuning method (ranging from
> "cool" to "you got lucky kid -- you're about to destroy your
> radio"), I'd sure appreciate them.
> 
> I'll talk to you this weekend on 222 from the N0RPM limited multi-op
> station in Woodbury.
> 
> Brent
> KD5EMB
> 
> P.S.  Thanks again to everyone who has given me suggestions, pointers,
> signal reports, and just plain encouragement while getting all this
> 222 equipment going.  Now the fun really begins!
> 
> -- 
> Brent Casavant            http://www.angeltread.org/
> 44.9067N 93.0558N 907F    -.- -.. ..... . -- -...
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