[NLRS] Club Cheap Yagi Build Day Advice Needed

[Chris Cox]

As a tip on how to work-harden copper wire to make it much more rigid, take a length of bare copper electrical wire - I've done upto six feet or so at a time - grasp one end in a vice or clamp and then insert the other end into the chuck of an electric drill.  Pull the wire taut and then slowly use the drill to twist a few turns into the taut wire.  You will find that the wire has become notably more rigid and suitable for use as antenna elements.

73!  Chris Cox, N0UK
chrisc at chris.org or chrisc at BritishCarAndDriver.com


> On Nov 16, 2016, at 00:10, Doug Reed <n0nas at amsat.org> wrote:
> 
> 
> 
> 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.
> 
> -- 
> "Democracy is two wolves and a lamb voting on what to have for lunch.
> Liberty is a well-armed lamb contesting the vote." - Benjamin Franklin
> 
> "When seconds count, help is only minutes away."
> Does Gun Control protect you, the criminal, or the Government?
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