"Dave Platt" wrote in message
...
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?
I'm a "single antenna" guy myself.
I think, in a truck, at least, that "big radio" is synonymous with "big
wris****ch". :-)
We can't mount the antennae high or center, because the 13', 6" height of
the truck is where the low bridges start.
Also, most tractors have this horrific system that intergrates AM/FM with
the CB coax.
A CB stick on the left mirror and an AM/FM on the right, and a splitter in
the coax, so I always run my own coax seperately.
And I have a cellular antenna on one side, any way, for dual plane signal
boost, and it has to be 8" (I think) away from other sticks.
But hhhhhere's a question for the braintrust:
I'm after a (mobile) VHF radio that's common to northern (i.e., the Yukon,
and Northwest Territories) Canadian truckers- who don't monitor CB bands.
(info
http://forums.qrz.com/showthread.php?t=171741
I'm sure, as a sine wave challenged layman, that I can't use the same
antenna and coax as my CB?
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.
--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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--
Popeye
"Best thing for him, really. His therapy
was going nowhere," -Hannibal Lector.
www.finalprotectivefire.com
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