[TowerTalk] 160m Vertical

[David Robbins K1TTT]

Into what lengths are the guys broken??


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of AB5MM
> Sent: Monday, October 01, 2007 02:44
> To: towertalk at contesting.com
> Subject: [TowerTalk] 160m Vertical
> 
> There seems to be a bit of confusion as to the tower height and the
> tower insulator location. It's probably in the way I explained it in the
> first post. Sorry about that.
> 
> A. Starting at ground level is the concrete base.
> 
> B. Out of the concrete base is a piece of  Rohn 25G, upside down,
> sticking up 4 ft.-3 inches above the concrete. (At approximately 6
> inches above the concrete is the ground radial buss bar bolted directly
> to two tower legs.)
> 
> C. Next is the insulator(s) and they are 4 inches in height. The
> insulators are made of high density (LGQ) fiberglass rod.
> 
> D. Stacked on top of the insulators is 120 ft.-6 inches of tower. The
> top section is a Rohn "flat top" with a 2" bearing. The bearing was
> included to accommodate the addition of a stinger if we needed it.
> 
> E. The guys are broken with the standard 5.5 inch (ANSI 54-3) porcelain
> insulators.
> 
> Almost all matching was attempted directly at the tower feed point. This
> consisted of a 15 inch RG8 pigtail, PL259 on one end and split at the
> opposite end for 5 inches. The center conductor attached to the tower
> just above the insulator, with the shield attaching to the base section
> just below the insulator. All the ground radials come to a common
> aluminum buss bar securely attached to the bottom base section 6" above
> the concrete.
> 
> The equipment used for trying to obtain a reasonable match are as follows;
> - RF signal source: MFJ 249, MFJ 259B and a CW exciter with variable rf
> output, 0 to 30 watts, 1.00 MHz to 4.50  MHz.
> - VSWR  measurement: The two MFJ analyzers. Two Bird meters, one meter
> with 50w slug (fwd) and the second with 5 watt slug. (rev) and finally a
> Yaesu YS-60 pwr/swr meter.
>  Only once, did I try loading the vertical from the shack. I used a
> 75ft. piece of Andrew LDF4 heliax and my Yaesu. Poor results... the swr
> foldback killed the output.
> 
> The matches tried are;
> Low pass "L"... series inductor 0 to 32uh with 25 to 1000pF capacitor
> shunt to ground.
> High pass "L"... series cap 250 to 1800pF with above inductor shunt to
> ground.
> High pass "T"... series 72 to1200pF cap, same variable inductor to
> ground, and then another 75 to1200pF cap.
> Low pass "Pi"... series variable inductor with two caps on either side,
> both are 572 to 1700pF.
> ??                  ... series cap 72 to 1200pF
> ??                  ... variable inductor, one end to ground, the other
> end to tower with RF in on the variable tap.
> ??                  ... variable inductor, one end to tower, the other
> end floating, RF in on variable tap.
> ??                  ... parallel inductor and 72 to 1200pF cap, in
> series with center conductor.
> 
> All variations of the above mentioned schemes have failed in one way or
> another. The ones that did marginally work have too high of a Q and are
> extremely narrow in band width.
> 
> As an absolute last ditch effort, I can use a Palstar AT4K antenna
> tuner. I personally don't like to use tuners and would much rather use a
> resonant antenna. A tuner is just a 'cheat' and one more thing that can
> fail at the most inopportune time. Nuf said abt tuners!
> 
> Well, that is our version of the "old collage try" and we seem to have
> failed somewhat. Maybe it's time to put back up the inverted L's and
> dipole.
> 
> Best regards and 73,
> 
> Steve AB5MM
> 
> 
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