On 2025-03-17 2:01 PM, ARTHUR BERNSTEIN via TowerTalk wrote:
For a capacitor I used a long length of Teflon, thin coax @ 39 pf/ft
> (?)Actually coiled it up on a 1” form.
Do you mean 29 pf per foot? That's typical for the small diameter
50 Ohm coax - RG58, RG303, RG316, RG393, RG400, etc.
> Total capacitance was about 1000pf +/-.
With capacitance that high (reactance that low), one would be better
served to calculate the length of cable as an open stub (even if it
is rolled up) rather than simply as capacitance per unit length.
> It might have been RG-302 or similar 50 ohm? Very thin, 1/8”?
RG303 is 0.17", RG316 is .098", RG400 is 0.195" and RG393 is 0.39"
73,
... Joe, W4TV
On 2025-03-17 2:01 PM, ARTHUR BERNSTEIN via TowerTalk wrote:
Before my tower came down I used a type of T on 160. Approx. 55 ft. Vertical with 2 sloping
top loading wires about 35 ft each. Fed on ground with inferior radial system. Had a
resonance (SWR wise) below the 160 meter band. It needed capacitance. For a capacitor I used
a long length of Teflon, thin coax @ 39 pf/ft (?)Actually coiled it up on a 1” form.
Total capacitance was about 1000pf +/-. It made the Z very close to 0 at lower band edge. It
had a 2/1 SWR bandwidth of about 100 kHz, which meant there was ground loss, though the VSWR
curve was beautiful. It worked fair, only because radial system needed to be improved. Before
I could do more, the tower came down after two wind events. The coaxial capacitor held up
under my 500 watts. It might have been RG-302 or similar 50 ohm? Very thin, 1/8”?
Art., N2KA
Sent from my iPhone
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