6m antenna project
metavox at earthlink.net
Mon Dec 3 08:58:21 CST 2007
Nice work taming a piece of RS crap. I am looking forward to seeing
your fine work before it gets all sealed up.
Michael Chisena wrote:
> All, I'm still working on finding antenna bases for the AS coil / whips
> that Frank has. After the Saturday Taco's meeting I got an urge to try
> my hand at something. Radio Shack of all vendors sells a base load
> magnetic mount CB antenna that uses the AS style whip and base. This is
> their 29.99 unit. I will bring it into tacos next Saturday if anybody
> wants to see it. In an old copy of the 'Handbook' there was an article
> on how to tune similar antennas into ham stuff. I think the article was
> for the 220 band. Anyhow, I got to wonder how hard it would be to make
> this work at 52MHz? On the plus side, i! f I had killed the coil/whip,
> I still had an AS style antenna base to work with. So the project would
> not be a total loss. I used my MFJ VSWR analyzer to do this. For those
> of you with the VNA tool, that might yield a more precise result.
> Couple of words about the antenna first. It's a loaded coil with a
> fiberglass whip. It has about four inches of adjustment range. A word
> about plastic products. You know how some plastics feel like quality
> products, and some simply don't. The plastic this was molded out of is
> in the second category. Strong but brittle feelings, almost too shiny to
> be real. The whole antenna radiated the feeling of 'cheap junk'. Just
> for the record. The antenna coil body seemed to be glued to the!
> internal parts. At the time I didn't know how to remove this plastic
> tube from the coil assembly. Ended up using a cut off wheel on the
> dremmel tool. You would expect a metal part connecting the coil
> winding to the antenna whip. No so here. It's a chrome plate plastic
> that makes the connection. I did say cheap. This thing is going to be
> loaded with 'bi metallic' issues after a few years of service. The
> copper wire is soldered to a brass pin, pushed into the plastic, making
> contact with the chrome plating. It works, but for how long. From the
> day this antenna was assembled it starting to deteriorate due to oxygen.
> Talk about a throw away product. After some dust and noise, I was able
> to cut a channel into the plastic, to the point where a screw driver can
> be pushed into it, twisted and cracked the tube off the coil assembly.
> Th! en the question of how to tune for a new frequency. I counted the
> windings. Five on the (lower) and 22 (Upper). With the stinger bottomed,
> it gave me a vswr curve in the 28 MHz range. So if I over cut the
> windings, I can compensate by raising the whip. I cut the upper coil.
> So two turns at a time I removed windings. Then replotted the resonance.
> Each time it moved a few MHZ up the dial. After a bunch of wire was
> removed it actually tuned up on 52MHz. Not too bad. I wish I knew more
> about how these things worked. I think the magic number was about 28
> inches (in 4 inch segments) off the top, and one turn off the bottom. I
> saved the cuttings and the tune notes for Saturday. Taking a t! urn
> off the bottom was a wild guess. I did it because the Z Gage was more
> than a little high. It proved out to be a right guess, but the how and
> why is not clean in the mind. Call it inspiration, not based on logic or
> thought. Anyhow, I'm going to firm up the solder joints and make it
> presentable. After the next taco's meeting I may spray it in plastic,
> and cover with heat shrink tubing. I want the brain trust to look it
> over and decide if it's sane or not. If I need to do a second one, I
> will boil the coil first to see if that frees up the glue the OEM used.
> Later kids Mike
> "You are, what you do, when it counts"
> The Masso
> "Gravity, the quickest way down"
> Mayor John Almafi
> "You ever drop an egg, and on the floor you see it break?
> You go and get a mop so you can clean up your mistake.
> But did you ever stop! to ponder why we know it's true?
> If you drop a broken egg you will not get an egg that's new?"
> MC Hawking
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> Tacos at amrad.org
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