Roy Lewallen wrote in news:13la97elqjdp5e2
@corp.supernews.com:

Owen Duffy wrote:
. . .
The helical problem I posed is not unusual, many if not most low HF
helicals wind up with close spaced turns at the top. . .

Out of curiosity, why?

Why are they made that way, or why my interest?

My interest harks back to measurement of field strength of emissions as
part of response to the BPL threat.

I was interested in whether NEC models might lead to a good estimate of
Antenna Factor of typical commercial mobile whips (eg Hamsticks) on a
wire frame model of a vehicle.

I did create some models of centre loaded whips in on vehicles, but I
could do a pretty close estimate of them without resorting to NEC
(http://www.vk1od.net/sc/slvaf.htm).

I wound up extending that to a piecewise representation of the helical
(http://www.vk1od.net/m40/index.htm).


Owen