Dear Rick:

Small (six element) LPDAs exist that have been used over the frequency
range of interest by amateurs and military. The SWR tends to oscillate with
frequency and the gain is reduced wrt to a larger LPDA, but they will work
for what you wish to do. Perhaps I have not interpreted "size" correctly.

I have some experience with wire LPDAs that point straight up. Many
years ago, a three (insert giggle) element was constructed to cover 4 to 6
MHz. Two towers. Three wires. It produced noticeable gain over a doublet.
I no longer remember how high the towers were.

An aside: 2:1 or 2.5:1 frequency coverage by a single LPDA is straight
forward. Larger ratios require one to consider more factors.

Perhaps one of the best antennas for covering the 4 to 5 MHz range is
the classic tropical broadcast antenna. At center frequency: two one WL
dipoles (fed in phase), 0.3 WL high and separated horizontally by 0.5 WL.
Bring the two, equal feeds to a central pole and place them in parallel. It
is possible to have a resulting impedance that is very acceptable. An
advantage of this system is that the coverage is close to being equal in
azimuth (at the TOAs of interest) and it has low sensitivity to distant,
interfering stations.

Consider investing in EZNEC and learning to use same.

Do let us know what your antenna system ends up being. 73, Mac
N8TT

--
J. Mc Laughlin; Michigan U.S.A.
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"Rick (W-A-one-R-K-T)" wrote in message
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On Thu, 16 Aug 2007 23:22:43 -0400, J. Mc Laughlin wrote:

For less than $1000 you may purchase and use a LPDA that will
accomplish what you specify. Several such antennas are on the market or
you could construct one from scratch.

Good morning, Mac.

Yes, the log periodic was my other alternative to the SteppIR (in fact,
the SteppIR was something I've been considering to mitigate the size of
the LPDA). It should do well for the higher frequencies of interest (14
to 24 MHz).

At one time I considered a wire log periodic, pointing straight up, as an
NVIS antenna for the lower range (2 to about 8 MHz). Then I went to
lie down until the thought went away. :-)