>
>Hi all,
>
>Well, it might not be specifically amplifier related, but I thought I'd let
>you guys now a little about the new antenna tuner I picked up at Dayton.
>Yeah, yeah, I know - some of you don't like to use tuners and load the amp
>directly into the antenna. Personally, I don't like that approach as I'm
>not able to accurately measure power under high SWR and I also like the
>added harmonic suppression of the tuner.
>
>Previously, I had an old Heathkit roller inductor tuner. It worked fined
>for the most part with full legal limit, but would sometimes have arcing
>problems on the load cap. The biggest problem was with my 80m dipole. It
>is cut for 50 Ohms around 3.6 MHz and there it gives a great match.
>However, as I move up in frequency, the match is very narrow. I start
>getting about a 3:1 SWR around 3.75 MHz and it gets worse from there.
>
>The Heathkit would arc even at power levels under 1000 Watts. I even tried
>removing one of the offending plates from the capacitor in the hopes that
>the larger air spacing would help. It didn't and in fact, made other things
>a little worse. So given this background I decided to look at antenna
>tuners at Dayton.
>
>My first stop was to look at the Ameritron/MFJ/Vectronics units. After all,
>they are the most prolific tuners out there right now. Upon looking at all
>these units, I found that the plate spacing on their caps were no better
>than what my Heathkit had. Even their highest power units had caps with the
>same spacing. It is interesting to note that later I noticed that the
>Ameritron tuner rated for 1200 Watts has larger cap spacing than the ones
>that are more expensive and rated for higher power!
>
>So I figured, buying one of these, probably wouldn't help at all.
>
>After this, I began working my way over to the booth of another company that
>I knew sold tuners - Palstar.
>
>I got to the Palstar booth and to my delight their tuners looked absolutely
>awesome. Plate spacing was at least twice and possibly three times larger
>than anyone else's. Construction looked to be of an excellent quality and
>the units were rated at 3KW or greater (if memory serves me).
>
>They weren't cheap. The AT4K with a built in antenna switch, LED bargraph
>and so forth was over $900. However, they were selling the AT4K-BAL which
>has a single input and a single output (either balanced or coax) and none of
>the electronic metering. This unit sold for around $700. Since this
>configuration was similar to the Heathkit I had, I decided that this was the
>tuner for me. First I wasn't going to buy it but wait a couple of months.
>Then I decided, "What the heck!" So I went and bought the unit they had on
>display.
>
>Well, upon getting the tuner home, I immediately went to 80M, tuned up and
>VIOLA! - NO ARCING!! So, I was like, COOL! I've used the tuner on just
>about all bands now at full legal limit and it works just great. It will
>even tune my 80 m dipole on 160 m which is something my Heathkit wouldn't
>do.
>
/\ The Heath tuner would quite likely have worked if you had a broadband
75/80m double-dipole -- i.e., two dipoles in an X config. One dipole
resonates at 3.6MHz and one resonates at 3.9MHz. The result is even
better than sliced bread.
.
>My only complaint about the unit is that the roller inductor is a little
>stiff and hard to turn in some spots, but that will probably get better over
>time.
>
/\ Finely-powdered graphite mixed with Mobil 1 5w oil might do just
fine. Use minimal oil so that the conductance of the lubricant will be
high.
cheers, Jon.
- R. L. Measures, 805.386.3734, www.vcnet.com/measures.
end
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