Roy Lewallen wrote:
JB wrote:

The frame is the only substantial ground and certainly most effective
for 40
meters. Use of the corners of the vehicle might actually get you a
counterpoise on 20. What you really need is a trailing wire, dragging a
cast iron stove.

At HF, a vehicle isn't "ground" or a "counterpoise", but the bottom half
of an asymmetric dipole. It radiates at least as much as the "antenna"
due to currents flowing downward along the outside. Calling a vehicle
"ground" or "counterpoise" doesn't impart magical properties -- it's a
conductor carrying currents whose fields don't cancel. In other words,
it's an integral, radiating portion of the antenna. You can't leave this
significant part of the antenna out of a model and expect the model to
give correct results.

I'm assuming that there is a capacitor formed by the car body being some
few inches away from the physical ground also?


And modeling a vehicle can be challenging because of the proximity of
conductors, particularly the whip and vehicle. You have to follow the
rules for closely spaced parallel conductors, and watch the average
gain. You might need considerably more segments than normal where
conductors are very close.

Given my limited experience, it's gotta be very difficult to model. My
setup was worst case, as far a sensitivity to bandwidth goes, a
bugcatcher. Best of a bad lot, I guess, but that makes the tuning very
sharp and sensitive. I'm assuming that the antennas that have fixed
elements "work" and tune by being pretty inefficient.

Which makes me suspect that we won't find any Hi-Q HF antennas that
aren't manually tuned in some fashion.

- 73 de Mike N3LI -