----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "topband" <topband@contesting.com>
Sent: Tuesday, August 20, 2013 4:00 PM
Subject: Re: Topband: RX antenna transformer winding (pure
resistancetransformation issues)
<SNIP>
Unless you have a system with pretty high common mode impedances, winding
spacing means nothing.
** Contrary to what you have stated elsewhere
The primary reason I (and DXE) isolate windings with
Teflon tubes is to reduce lighting damage, and to greatly reduce assembly
damage. If the system has pretty high common mode impedances there might be
some small advantage in pushing windings apart, but the primary-secondary
capacitance is never going to be important in Beverages or other low or
modest common mode impedance antennas. Balancing a small loop might be an
issue.
** Common mode is an overworked response for perceived ailments.
I took your low capacitance suggestions a step further after carefully
measuring C and frequency response for maintaining high directivity and F/B.
Many Topband operators use their Beverages above 2 MHz.
I started using Teflon sleeves in windings because I ran out of small Teflon
wire wrap wire I was using. Without Teflon on the wires, and with normal mag
wire, the enamel was easily scratched. Not only that, lightning would punch
through from enamel to core, or from wire to wire.
** Telon is easily nicked, the type of wire used in modern vehicles is very
robust but with the sleeves plain ole magnet wire works well and allows even
smaller winding bundles.
Since I was more interested in performance rather than production problems I
took the time to evaluate a large number of variations.
Carl
KM1H
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Topband Reflector
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