On Wed, 31 October 2001, BILL STRAW wrote:
> Are these two feed methods equivilant?
Assuming a goal is to match the vertical's feed-point
impedance of 30-something ohms to 50 ohms, those two
methods don't sound to be equivalent to me.
In fact the second method sounds backwards.
> When I built the 40M 4 square, the then owner of
> Comtek told me to use a multiple of 1/4 wavelength
> 75 ohm coax (I think I have 3/4) so it would reach
> between the box and base. A lot of coax, but it works
> great.
Odd multiples of 1/4 wave of 75 ohm coax is one way.
> When I built the 80M 4 square, the owner of DX
> Engineering told me to just use equal lengths of 50
> ohm coax to drop down from the elevated bases to the
> ground, then hook up the 1/4 wavelength 75 ohm coax.
> This also works great.
That doesn't sound quite right to me.
A 1/4 wave of 75 ohm coax attached to the feedpoint transforms
33 ohms up to 50 ohms. From that point, equal lengths of 50 ohm
coax can be added to each feedline in order to reach the box.
Whatever approach is adopted to connect the elements to the
phasing box, all four of the lines should be identical.
73,
Mike K1MK
--
Michael Keane K1MK
k1mk@alum.mit.edu
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