Topband: NE Dipole vs Vertical with Coupling Effects

[John Kaufmann]

On Fri, 10 May 2002, Bill Tippett wrote


>         I'm surprised the 80 meter data Bob provided
is so close
> to 160 since my experience has been that high 80M
dipoles work
> very well compared to verticals.  


I think the consensus in New England is that high
horizontals, up 1/2 wave or more, outperform verticals
on 80, at least for inland locations.  My vertical
array (located right next to a swamp, with an extensive
radial system) works well against most of the
competition on 80 but just can't match the high
horizontals.  Verticals over salt water are a different
story, although there aren't many in W1 land.  Like
Bill, I find it surprising the 80 and 160 coupling
numbers are so similar for horizontal polarization.

Here's a quick and dirty numbers comparison for
horizontal vs. vertical on 80.  Since I'm lazy, I'm
just recalling some of the gain numbers from memory,
and I could be off by a dB or so.  A single vertical
over "mediocre" ground, typical of New England, has
about 0 dBi gain at 20 degrees elevation angle.  A
2-element Yagi at a height of, say, 150 feet on 80 has
about 12 dBi gain.  The Yagi numbers are similar for a
2-element quad.  Let's use -1 dB of coupling loss to
the NE for the vertical, assuming 80 is like 160, and
-9 dB for the horizontal, extrapolating just a bit from
Bob's data for 20 degrees.  Then the "effective" gain
of the single vertical, taking coupling into account,
is -1 dBi and the Yagi is 3 dBi.  In other words, there
is less than 1 S-unit (assuming 5 dB change per S unit)
of advantage for the Yagi over the simple vertical. 
This, I think, would come as a surprise to the people
using those big horizontal arrays on 80.  If we convert
the vertical to a 4-square, which picks up about 5 dB
of gain, then the advantage shifts to the vertical
array.  Anyone else with 80 meter experience find this
surprising?  Are there other factors which make this
analysis too simplistic?

Another question:  Bob has said that his coupling
numbers "only apply to the first and last transits of
the lower ionosphere".  If we assume the ionosphere
randomizes the polarization (true?), are any additional
losses incurred in multiple hops (and therefore
multiple exits and entries) more or less independent of
the initial transmit polarization and therefore random?

73, John W1FV