[NLRS] 6m rover antennas

[Dr. Gerald N. Johnson, electrical engineer]

Low antenna height is going to kill off low angle signal strength, no
matter what the modeled surface.

The van is going to affect element impedances, but probably the earth is
going to set the vertical radiation pattern from reflection beyond the
van.

Remember when working in half space (over a ground plane) all the NECs
use half isotropic as the reference and show the gain 3 dB high.

Thin rods for elements will stretch their length and so may not decrease
wind load to the point they can survive. It might be better in a rover
to go short with end loading (perhaps capacitor hats) to cut the width
for transport. Buggy whips do survive wind well, but can the van stand
their drumming while going down the road?

While the lowest elevation angle is desired for tropo and F2, many times
6 meter E propagation works better with higher angles of radiation
because the reflection clouds are relatively nearby and relatively high.

There always have been yagi designs that appear to be locally optimized
that work poorer than NWS designs. The optimization process tends to
produce a waffled gain surface with many local maxima, its often
necessary to jump away from a local maximum to find other local maxima
and to pick from the best of those found.

It is possible to beat the NWS designs but difficult to beat them by a
great deal. DL6WU designs work a little better for long yagis and have
better driven element feed impedance and better bandwidth. Any
propagation path over a few miles will have more signal strength
variation per second than the difference between a NWS design and any
computer optimization. Often computer gain optimization trades off
bandwidth or a reasonable feed impedance. Sometimes a low feed impedance
(close spaced first director) causes excessive circulating current in
the driven element and first director to cause greater loss than the
optimized gain advantage.

Any working antenna, come contest day, is better than the antenna that
exists only in the computer.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.