At 09:15 PM 11/21/97 -0700, Steve Zettel wrote:
>I am going to be hanging an array of three 80M vertical dipoles from my new
>tower, similar in concept to the description Tim Duffy K3LR, et al
>published in the ARRL Antenna Compendium, Vol. IV.
>Right now I'm in the process of building a relay box to do the switching.
>At this point it would be easy to incorporate another relay to switch
>additional loading in and out of the circuit to enable the antenna to play
>at both ends of the 80M band. But I am a little fuzzy on how best to
>accomplish this. I think I want to tune the system "as is" to the lower end
>of the band (Pete Smith's recent comments indicate the antenna is more
>forgiving above resonance than below) and then switch in some reactance to
>the driven element to make it appear electrically shorter than it is.
>Should I just leave the reflectors and their feedlines alone and let them
>appear to be longer and longer electrically as I tune higher and higher in
>the band, or would it be worth the additional complexity to attempt to
>switch reactance in to them too? I forsee THAT getting VERY complicated.
>From my modeling of the antenna, there's no reason to try to shorten the
reflectors. The F/B falls off very gradually above the resonant frequency
-- it's still quite useful at 3.9 mHz, with an antenna cut for 3.5. I
don't have a clue what sort of network you'd need at the switchbox ro
shorten the driven element -- if you get any good answers please publish!
I'm using a switchbox for 4 elements that requires only two control wires -
based on the old Heathkit switch design that used the coax. Works great.
I confess that I run in the DX window on 75 with the SWR "as is." My
SB-220 will tune under those conditions, and I figure the losses/cable
heating are tolerable for short QSOs. But I'd even consider running
another pair out there if I could see 1:1 or thereabouts on SSB.
>On a separate but related note, I tried following the URL posted several
>months back to the CATV home-brew connector page published in TowerTalk
>awhile back, but the page is "Not Found" anymore at
>I have several miles of 1/2" and 3/4" CATV given to me after a local
>windstorm ripped through Libby this summer and I'd like to dope out how to
>economically make some connectors for it.
K9UWA gave me the recipe for 3/4" CATV -- a brass reducer fitting for 1/2"
copper tubing to 1/2" water pipe. Take the innards out of an Amphenol
barrel connector (they have a snap ring in one end) and solder it inside
the small end of the reducer, with the non-snap-ring end out. Put the
center part of the barrel connector on the center conductor of the hardline
and (with appropriate fiddling for length, etc.) screw the reducer (with
the closed-end teflon parts already inside it) on the end of the hardline
jacket (Noalox helps). Tape well. That's it.
73, Pete Smith N4ZR
"That's WEST Virginia. Thanks and 73"
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