Michael Coslo wrote:
I'm putting together a homebrew mobile antenna based more or less on
"20 dollar mobile antenna" that appeared in QST some years ago.

For those not familiar, the antenna consists of a tapped coil at the
bottom, a spiral wound lower section, a tapped loading coil, and an
upper stinger.

My question involves that spiral wound lower section. What would this
be thought of? As antenna below the loading coil, as an inductor in
addition to the other two, or some sort of hybrid of antenna/inductor?

How would this be modeled in EZNEC?

Apologies in advance if this was an incredibly stupid thing to ask! 8^)


- 73 de Mike KB3EIA -

Hi Mike,

Anything other than a straight conductor would add inductive loading, with
less (if any) contribution to radiation. Close spacing of the inductor turns
will add distributed capacitance. The closer to the feedpoint, the greater
the I^2*R loss and the larger conductor should be, to keep the loss as low
as possible. So, electrically, the best place for loading is at/toward the
top end.

My mobile antenna setup consists of Hustler/Newtronics parts... but not
quite out-of-the-box. For 20m, I use their RM15 (15m) loading coil + a 49"
whip with about 6" cut off of it. The whip came from Larsen (pn W490).
Though this effectively moves the loading coil toward the high-current end,
it adds considerable radiating surface area. When the band was in, it was
good enough to work the UK (using 100W) from my QTH near Seattle! I haven't
(yet) tried an RM12 loading coil with an even longer W640 (64") whip. My
setups for the other HF bands are similarly taller than the Hustler setup...
the 75m antenna is quite tall! :-))

Bryan WA7PRC