Lloyd, et.al.:
10 sections of 25G add up to about 97.375 feet since the legs telescope
about 3.5 inches at each joint. If you put the 6 meter beam on the top of
the 2 inch diameter 10 foot high mast, assuming the reflector and directors
are grounded to the boom, you will have between 15 and 20 feet of top
loading.. it is best to model it and find out.
That would mean the electrical length could be between 122 and 127+ feet or
resonant somewhere between 1840 and 1920 KHz. Since one does not get much
radiation off the top 25% of a quarter wave vertical, I would recommend
enough top loading to at least get down to the center frequency of interest,
where the impedance will be Zant = 36 ohms plus ground losses. If you have
a very good radial system, that could mean the impedance, Zant = 36 + 0 ohms
ground loss. That would mean about 30 feet of wire on each guy line from
the top of the tower down toward the guy anchors. If your ground is very
good, consider another 10 to 15 feet of top loading (40 - 45 feet of wire on
each top guy line) to bring the impedance up to Zant = 50 + jXL ohms and
then tune out the inductive reactance with a series capacitor at the feed
point. The inductive reactance could be around +60j to +80j ohms which
would be tuned out by a capacitor in the range of 1000 to 1500 pfd at 1830
KHz.
73, George K8GG
----- Original Message -----
From: "LLOYD CURRY" <na4d@kih.net>
To: <topband@contesting.com>
Sent: Thursday, September 25, 2003 1:05 PM
Subject: Topband: capacitance hat
> I am about to finish an insulated tower vertical. I have a 10 foot
section,
> then an insulator, then 100 ft of 25g and a 10 ft mast out the top. The
> tower is insulated with Phillystran guy wire. How much capacitance hat
> will I need to resonate to about 1830 khz? Should I put it at the top of
> the mast or is where the mast exits the top section ok? Finally, I am
> considering placing my Cushcraft 6 el 6 mt. yagi (20 ft boom) on this
> tower. Will it provide enough capacitance? Any comments will be
> appreciated. Lloyd Curry NA4D
>
>
> LLOYD CURRY
> na4d@kih.net
> Why Wait? Move to EarthLink.
>
>
> _______________________________________________
> Topband mailing list
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>
>
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