[NLRS] Club Cheap Yagi Build Day Advice Needed

[Doug Reed]

My comment would be to use a Teflon coax cable for the first two or
three foot of the cable because it will be much easier to solder short
leads if the shield doesn't melt though and short to the center
conductor. Goop it up good to keep the water out of the cable braid.

Don't discount cheap crimp-on BNC connectors for RG58 cable. They are
good RF connectors and low mass. I used them on a lot of my old
installations because they would mate with my HT. They are still
lighter than UHF connectors and cheap to find adapters, plus half-turn
on-off. I still have UHF to BNC adapters on my mobile rigs.

If you can gather test equipment, I recommend something that will
sweep the band and show the return loss (SWR) so you can see the
results of your attempts to change it. The design is intended to be
fairly insensitive, but I did some checking on Bruce's antennas last
fall and found that bending the hairpin wider or narrower, forward or
back, tended to optimise the SWR but I still had to trim the length on
a couple to bring resonance to where it was wanted.

I'd have sworn Kent published dimensions for a FM version of the
antenna centered at 146.52 or 147.0MHz, but I can't find it. Donn
suggested shortening the elements 1/2" for FM. If you compare the
element lengths and spacings in the original article and the LEO
antenna article, both on Kent's web page, you'll see he shortened the
elements 1/2" for 145MHz. I'd suggest you can probably shorten the
elements about 1"-1.5" from the original 144MHz lengths to get 146MHz.
If you are real brave you could try shortening the spacing dimension
slightly too, but it probably would not make much of a gain
difference. I haven't tried this, so Caveat Emptor!

If I was building the antennas for myself, I'd probably guild the
lilly by cutting the length of the coax pig-tail to be a half-wave
multiple (including velocity factor) on the band of interest. I'd be
doing this so the antenna impedance at the connector was the same as
the impedance at the driven element, with minimal odd effects from
impedance miss-match and cable length. But that is probably over-kill
since these are intended to be emergency antennas not laboratory
reference antennas.

Donn's comment about water-proofing the wood is dead on if the
antennas will be left out in the weather. Any sort of paint or varnish
is better than nothing. My personal favourite is half-n-half Boiled
Linseed Oil and Turpentine. It soaks in and water proofs the wood very
well. But the ingredients are fairly expensive if you only need a
quarter cup for an antenna. Any sort of common wood preservative will
work. I've also had good luck finding remnant quantities (quarts &
gallons) of Thompson's Wood Sealer (and others) over at the local
county recycling center at no cost to me.

Jerry's comments remind me that the Cheap Yagi LEO article suggested
soldering hobby tubing on the end of the driven element if it was too
short. That also solved the "I've cut it twice and its still too
short" tuning problems.

I'm glad to hear you're doing this "build it" session. Small club or
community projects like this are a feature of hamfests in England. If
this goes well, maybe you'll consider doing a similar session at the
Buffalo hamfest, assuming they have a room you can use?

Good luck with the project!

73, Doug Reed, N0NAS.

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