Some answers...(questions below) de N4KG
(re: L - network)
I used a standard 2 inch diameter coil of #14 or 16 wire fairly
closely spaced (10 or 12 turns per inch) and an air variable
capacitor with 1/4 inch spacing. Of course, high voltage
capacitors can be made utilizing RG8 or RG213 which
exhibits approximately 30 pf / ft. Be sure to keep the cable
under 1/8 wavelength to ensure that it remains capacitive.
Parallel lines can be used to increase capacitance.
The small diameter guy wire 6 - #18 has become more
difficult to find. Radio Shack has some light guy wire
but it tends to rust in a few years. RS also carries
insulators.
To prevent guy wire interaction, the spacing between
insulators needs to be sufficiently less than a half WL
wavelength at the lowest frequency used near the guys.
On TEN meters, 11 ft is a good number. As you noted,
this requires a LOT of insulators. Non-conductive
non-stretch guys may be a better choice. The smallest
size Phillystran from Texas Towers is one option. For
masts with no large top load, perhaps a non-stretch
rope could be found. HyGain uses a braided plastic
(I don't recall the material type) for their verticals and
may be willing to sell this separately. Check CQ and
QST for dacron rope suppliers and ask about stretch.
I suspect the great radial debate is far from over. I am
in the process of installing a full size 80M vertical and
radial field in my woods to compare that with my
elevated GP. W8JI has made some field strength
measurements using a loaded vertical over an
extensive ground based radial field and an elevated
radial field. His results favored lots of ground based
wire. This of course was measured at ground level
using the surface wave. I am not sure if higher
wave angles will correlate directly with the surface wave.
There is an extensive study of field strength vs. number
and length of BURIED radials published in the June 1937
issue of the Proceedings of the IRE. Other studies claim
that elevated radials or insulated radials on the ground
provide equivalent performance with fewer radials. I'm
not sure about their methodology. Measuring field strength
at the desired wave angles will provide the answers.
Anyone have a helicopter and LOTS of time on their hands?
de Tom N4KG
.............................
On Tue, 9 Dec 1997 07:46:15 -0800 (PST) ftbrady@earthlink.net (Frank T.
Brady) writes:
>Hi gang, it's me again, with still more questions:
>
>Looking for (least expensive, if possible) sources of:
>
>* High voltage inductors and caps for the L-Networks at the base of
>half
>wave verticals.
>
>* Six strand 18 guage galvanized guy wire - approx 1200 feet..
>
>* Strain insulators for breaking up the guy wire - approx 120.
>
>* Verification that 11 foot segments are the best length to use when
>breaking up wire guys.
>
>On another note, I finally got my own copy of the Communications
>Quarterly
>article nixing quarter wave verticals. VERY interesting stuff!
>However, I
>ended up wondering: if avoiding radiation from the radials is the
>goal, why
>wasn't anything said about the radiation introduced by
>sloping/drooping the
>radials. I thought that also caused the radials to radiate. I think
>that
>the 1/8 wavelength radials for 7mhz and above elevated verticals could
>be
>brought out perpendicular to the radiator without too much mechanical
>difficulty if radiation from them is so important to avoid (the
>construction
>would look similar to a capacity hat, with stiff non-metallic struts
>going
>from the radiator up to the ends of wire radials, or even use aluminum
>tubing as the radials and support them from above with kevlar.
>Perhaps this
>wasn't considered because most of the serious researchers are
>interested
>only in 80 and 160? But even on those bands compromise 'loaded'
>radials
>could be brought out perpendicular without too much effort
>(considering how
>much effort these guys are willing to go through anyway).
>
>No doubt I'm missing something - but I thought I'd try to find out
>what.
>
>Thanks, and 73s
>Frank T. Brady - W0ECS
>Wildomar CA
>
>
>
>
>
>
>
>
>
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