> > My question is what is the ideal width for the spacers ??
> > tnx Steve
> I wonder if Steve ever got his question answered, about the IDEAL
> WIDTH ?
It depends on many things, but any changes affecting loss can be
tossed out because overall the loss is so low it doesn't matter.
The biggest problems are mechanical and how the impedance fits
into your system.
Mechanically, you want a wider spacing because the line is easier
to build.
Electrically, you want the closest spacing possible. It makes the
line less critical to surrounding objects, it also makes the
impedances presented at the end of the line more moderate on
most bands when you feed unmatched antennas...like a 80 meter
dipole fed with open wire to work all bands. Close spacing also
minimizes radiation.
I use about 3 inches and solid bare copper wire.
I have a 1500 foot long line using #8 solid copper wire spaced 2.75
inches, and the measured loss in 1500 feet of length (when
matched) is about the same as 100 feet of RG-213 except on ten
meters and above, where radiation starts to be a problem.
By the way, avoid feeding 1/2 wave dipoles with lines near an odd-
quarter wave long or multiple of an odd-quarter wave. You'll get real
high impedances on a few bands, especially if the line impedance
is high. For example, with a 600 ohm ohm line you'll get maybe
6000 ohms on the lowest band...and a similar impedance on the
next band up when the feeder is 1/2 wl long on the lowest band.
Use a 1/8th wavelength or 3/8th wavelength (etc, odd-1/8th wave)
feeder on the lowest band, and the impedance is moderate on both
bands.
The Match Box won't handle wide impedance ranges like a T
network will.
73, Tom W8JI
W8JI@contesting.com
List Sponsor: ChampionRadio.com - Trylon self-supporting towers,
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