Re: NEC-LIST: Why coil-load?

>I think the vehicle/whip can be thought of as an asymmetrical dipole
>rather than a monopole. I will run a simulation of an auto and see what
>it looks like.
>
> Dave Cuthbert

Okay Dave, call the antenna what you like, I do not disagree that the
antenna system (monopole + vehicle) is an asymmetric dipole. My
recent analysis included wire grid models for the vehicle.

You can have lots of fun with realistic models, at frequencies in the
vicinity of vehicle resonance (60-100 MHz range for vehicles we use).
You will find you can have unexpected pattern nulls, and lots of
current on the frame of the vehicle.

I carried out a whole series of analysis (using NEC-4D) for VHF/UHF
antennas on a mini-Van, but I had no measured data for comparison.
And the model is very dimensional sensitive: is the whip resonant or
not? If the whip is half-wave resonant, for example (all my previous
remarks were directed toward centre-loaded whips for HF) there is
little current on the frame of the vehicle. I gave up trying to
write a compact summary of my computational results --- and we have
large reader forum out there who do not believe in NEC!!!! So you
have to be absolutely sure that your model is right, or measured data
to support computational results.

73, Jack, VE2CV

References

Belrose, J.S., "Short Coil-Loaded HF Mobile Antennas: An Update and
Calculated Patterns", ARRL Antenna Compendium Volume 4, 1995, pp.
83-91.

Belrose, J.S. and L.Parker, "A tunable all-bands HF Camp/Mobile
Antenna", Communications Quarterly, Fall 1998, pp. 47-57.

-- 
The NEC-List mailing list
NEC-List_at_robomod.net
http://www.robomod.net/mailman/listinfo/nec-list