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Top

(Dave Platt) wrote in
:

In article
, Douglas
W. \"Popeye\" Frederick
wrote:

You still didn't give any useful information. No surpise
since you have none. For an average of the cb band
running 1/4 wave the antennas should be spaced 54 inches
apart. Use a commercially produced cophase harness if you
can find it. Make sure you match the SWR and you will out
do any other mobile off the front or rear.

Top

Thanks Top!

I think that Top's calculations (and recommendations) are a
bit off?

CB has an 11-meter wavelength. There are just over 39
inches in a meter. Hence, the wavelength is around 430
inches.

A 54-inch separation is only .12 wavelength. From the
chart in the ARRL Antenna Book, it looks as if you'll get
less than .5 dB of directional gain, compared with a single
radiator of the same type and size. That's less than one
tenth (!) of a nominal S-unit. You'd be very hard put to
be able to detect this small of a difference in practice -
it'll be less than the amount of signal variation you'll
encounter due to reflections from nearby objects.

In terms of getting yourself a directional-gain benefit, I
think a co-phased two-radiator broadside array with a
54-inch separation is essentially useless on CB
frequencies. There just isn't enough gain to matter.

Now, as somebody else suggested, using such an array might
get you a more consistent near-omnidirectional pattern than
a single radiator would deliver, if your antennas are
mounted less than optimally (e.g. on your sideview mirror
post). Using two co-phase antennas might be worthwhile for
this reason, even if you don't get a significant amount of
directional gain.

I suspect you'd get more bang for your buck by simply
mounting a single antenna in a better location (e.g. roof
mount) and paying attention to making the antenna's
grounding to the chassis/groundplane as direct and solid as
possible.

Cophase being omindirectional? You need to do some more
reading before you try to correct anything.