The L antenna mobile, (or fixed)

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From: rohre (rohre@arlut.utexas.edu)
Date: Tue Apr 07 1998 - 17:45:34 EDT


It is interesting how old ideas seem to reappear. In Don Johnson's prior
edition of his Mobile Antenna Handbook, he tells of early 80M (or 160?)
operations where a whip was extended with a wire to another whip mounted on
the front bumper of the vehicle. The whole thing was loaded as an extended
whip folded over for the low bands, and worked great!

Two 8 foot whips, and the wire in between made a folded over Ell antenna. The
base of one whip was fed, and the other was just insulated from the vehicle
bumper.

When you have less than a resonant length of antenna as in a LF mobile set up,
any more that you can get in length is better it seems. As most of the
interest of the W6 mobileers was in talking around town or state, the Near
Vertical Incidence Signal, (NVIS), propagation the folded over antenna
produced was ideal for their objectives.

I guess if one were to use two 8 foot whips, the task might be how to
efficiently fasten the stainless steel whip tops to the connecting wire.

Another idea more to the set up imagined in the post, is to simply do the Ell
as an Inverted Ell, and bring a wire down at an angle from the top of the
whip, but tied off with insulator to the front of the car.

Now if you wanted a killer signal mobile QRP for 160M, I suppose you could use
THREE whips, like two on the back and one on the front, with one of those in
back only as a support for the wire from the driven whip, across the width of
the car, and then up to the front connected whip. I would guess you could
have 32 feet plus of radiator that way. That means, on 40M, you could have a
full quarter wave mobile!!!

Let's think also about the apartment dweller with his need to have a low
profile set up. Rather than having an indoor antenna, maybe this could be
done on a building with/ without metal siding or frame, by running such a
antenna on the outside balcony! Place the two whips angled out from the
balcony, with thin wire in between, and feed one whip at bottom with a tuner,
insulating the bottom of the other. This should be fairly hard to notice, or
if they do, hang a flag on each! With metal siding on the building, of course
you have a reflector and shield effect in some directions. But, it still
might be better than the indoor antennas some try to run inside a building.

Some field will be canceled, no doubt in both the mobile and fixed case, but
the extra length of antenna might increase the efficiency overall.

Don't know if the modelers can handle such cases or not, but it might be
interesting!

I do know that the Marines and other forces are using the folded over extended
length whips to produce mostly NVIS radiation from the Humvees, to improve
tactical communications over traditional mobile whips.


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