[FoxHunt] Flex Ideas

[J. Craswell]

-Ques: Is your Felx-o Yagi based on the design Ive seen by WB2HOL(yes I know
the
-dimensions are different). Your Web page is GREAT(I mentioned it on the
NHWG
-mailing list), but the yagi construction could use a bit more detail. Are
the
-flex tapes clamped to the boom using the PVC Tee's? Do you use any sort of
-decoupling on the coax? I would like to see the specs for the 5 element
version
-sometime. This could be a fun project for the Cadets(and us old folks,).

Thanks for the nice words about the web page.  It's not too advanced - I'm
not a HTML guru so I appreciate your response!
I can't claim to have invented the idea because WB2HOL had one a long time
before I did.  I was thinking of it from the view of those old PRC10 Radio
Antennas and wondering if the "flex" antenna might not be the same stuff as
a measuring tape.  I took one that had been goofed up and cut it and tried
to solder to it.  I was thinking how great this would be for an antenna that
would take the abuse we put our L-PER antenna through when I did a search
for Flexible Antenna and saw his site.  Great minds must work alike.  It's
just that mine is a day late and a dollar short.  My invention of the light
bulb is next <grin>  I have to admit my experience with making antennas is
limited to maybe a half dozen wire antennas and a homebrew 3 element Yagi on
50 MHz.  I started the design with paper and calculator and then tried some
of the shareware.  The biggest problem I came up with was that some programs
reported different F/B ratios and that frankly had me stumped.  I wrote the
ARRL with my proposed design and they verified it using the Lab computer.
The F/B seemed unreal to me but....  It does work like a charm.  I would be
glad to run up a 4 or 5 element version for you.  I was thinking of that
myself.  The first version uses some PVC that is rather small.  For 3
elements it works great but anything larger might be too much weight.  The 6
element (I added one more) 243 Yagi uses the new fatter PVC and here I think
maybe I should have opted for the prev smaller stuff.  Either way they work
great and they can't be hurt unlike all the bent to hell L-PERs that show up
at our annual Foxhunt.  Whoever uses the Gun Cases is smart.  This is a good
idea as that Aluminum? wire antenna on the L-Per is made to get all bent
wrong.  *Say how many have seen guys bend the L-PER to look like an arrow
"pointing here?"  <sigh>

2 and 3 November 2002!  If you can make it come on out.   The 2nd is a pure
training day rehearsal.  The 3rd is a competition.  Small teams start at 15
minute intervals and you try to find all the Training Beacons and make it
back to the Finish line.  Some USAF folks are there to do a little eval on
ES (*Plus they like to hide the beacons) they are also the official Umpires.
Our Group 4 Commander and the USAF folks do the honors presenting a very
nice Trophy for the team with the best score.

I'll try to post a exploded drawing of the connections to the Driven Element
later tonight.  The tape is "open" (two pieces) shield to one and center
conductor to the other.  You need to scratch off the Paint on the measuring
tape to solder it.  Don't use too much heat for too long as it un "springs"
the metal.  Or so I'm told.  This design uses the Hairpin match also.  I got
1:1 SWR testing on 121.775 using an Av Band HT without any fooling around.
*Note no one was more surprised than me that it worked so well.  I'm trying
to do away with the hose clamps.  BTW The red portion is Heat Shrink tubing.
Punching holes into spring steel and using screws might be better.  I'll
report back when I finish the 6 element 243 design.  The PVC Ts have a hole
cut through them and I use short stubs of PVC on the sides to hold down the
tape in the proper form.  There is a slight "bowing" but it doesn't seem to
be a problem.  All the parts are held together with screws.  The PCV cement
might work ok as well I never tried it.  BTW cut the exposed ends in a
crescent.  Squared off these things are deadly weapons.  Spring steel makes
a nasty cut.  In addition also use Black tape or Duct tape on the ends so
you don't slice up your team mates.  The 3 element units give a really sharp
peak and good weak signal reception.  Too many elements "might" make the
beamwidth too small?  But that's unknown.  Right now I know this is a good
thing.  Easy to hump around in the woods also.  We showed it off to some
visiting members by walking quickly through a crowded room letting the
elements get all bent up and of course they come right back.  Our training
in the brush gives the same results but of course many of the folks on this
list have been there and done that for a long time I suspect.

-How reliable do you find
-SARSAT hit data. One positive asspect, Ive seen is that the lat/lon plots
have
-gotten MUCH better from where they were 10 yrs ago. But Ive also seen many
-instances where the satellite did not pick up an active beacon signal at
all, or
-only produced interitent hits. Have they "tightened the squelch" on the
receiver
-so as to reduce false hits? I know that the angle of elevation for a given
orbit
-can greatly affect accuracy too. Although Im still amazed at times as to
what
-the SARSAT DOES pickup, like the old EPIRB that had its antenna removed;
the
-satellite was only seeing it's 243 signal.. Or the EPRIB we found floating
in a
-pond directly next to a garbage recycling center. One of the things that
makes
-ELT/EPIRB tracking easy(er) is that the tx power they produce is all
roughly the
-same, about 100 mw. This seems to produce a somewhat consistant range
-"signature".

You know that's a good question.  My early missions proved (I thought) that
SARSAT hits were wishful thinking.  Ballpark only.  Unfortunatly I've worked
with guys who would be hearing ELT hits and turn the wrong way because
SARSAT said so.  I got very "anti" SARSAT except to put you close enough to
hear it.  At "times" they have been close.  Other times they have cycled
around an area but not the right one.  At least that's my impressionOur MCs
have been pretty active in looking at SARSAT "drift" and other things I
can't claim to understand.  All I ask is get me to where I can hear it and
we will find it.  In the classtoom what I teach is don't use the SARSAT lat
long to go to that exact spot.  Instead use that to go to the highest ground
near that spot.

BTW is anyone wants one I'm temporarily out of work and I'll be glad to make
these antennas up for a small fee.  I'm also running off some PCBs of the
Offset Attenuator (I didn't invent that either) for a switchable 243 / 121.5
unit to plug in ahead of a 2 Meter Handy.  No need for the L-PER and if
enough members have them (and are active) you can really do some nice
triangulation with them.  Plus no crystals so you can train on whatever you
like.

Question:  Who trains on the 243 Band and what freq and how do you "ok" it?
I'm getting conflicting answers on the availability of a training channel
and who authorizes it's use.

One tip I learned the hard way.  Driving around the burbs looking for an ELT
and the little hills in the area ALL showed a strong signal.  Knife Edge
refraction?  Anyhow getting on top of a hill (And fighting the killer
poodles to get there) solved this problem.  Unfortunatly the terrified
housewife wouldn't answer the door or phone until her son came home.  Then
she threw open the door tossed the ELT to us and slammed it shut again.
<grin>

Thanks & 73!

Jay W0VNE
http://www.mnwg.cap.gov/130th  Our CAP page.  Check out the RDF page.
http://www.dover.netfirms.com/  my home biz site.