"Dave Platt" wrote in message
...
I like them two at a time--co-phased. Is there any gain to be had that
way
or am I just skin pipe dreaming at the petro?
If fed in phase and spaced correctly, there could be gain to the front and
to the back with a decreased propogation to the sides.
This is usually desirable if traveling on a mostly straight stretch of
highway. I think the spacing is a little too far apart for use on most
cars.
I believe you're correct. This is a "broadside array" configuration.
Its gain over a single radiator rises roughly linearly (measured in dB
over a single radiator) up to separations of around 5/8 wavelength. A
separation of 1/2 wavelength gives around 4 dB gain over a single
radiator and a very nice clean pattern (deep null to the sides) - this
is the spacing most frequently described in the literature (e.g.
Kraus, Terman) for broadside arrays. Gain maxes out at just under 5
dB at a 5/8-wavelength spacing (at the cost of a small side-lobe).
[Figures are from the ARRL Antenna Book of a few years ago]
Whether it's worth doing for a vehicle-mobile system is another
question. You need more than .4 wavelengths of separation to get 3 dB
of gain (half a nominal S-unit) - at 11-meter frequencies that's around
14 feet of separation, which I think not many vehicles will allow.
Perhaps if you're driving a "wide load" transporter truck?
At 6 feet of separation between antennas you'd have only around .2
wavelength, which yields less than 1 dB of gain over a single
radiator. Hardly seems cost-effective.
It might make more sense for 2-meter operation... but as most 2-meter
mobile seems to be repeater-based, you really want omni rather than
shaped-beam-down-the-road most of the time.
There's also the matching issue. Each radiator in the array will have
a feedpoint impedance different than what would have if used alone.
You'll have to take this into account when designing the phasing
harness, and you may need an impedance-matching network at the
combining point to establish the 50-ohm load that your transceiver
expects. If you don't match properly your transceiver won't see the
load it expects, and may not deliver full rated power into the load -
you could easily lose more signal strength this way than the array
will gain back. If you do match properly, there will be some amount
of loss in the matching network.
There ain't no free lunch, alas.
Wow, Richard.
This guy seems 7 ****loads smarter than you.
Wonder if he ever "held an FCC license for radio work"?
--
Dave Platt AE6EO
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