Topband: horizontal/vertical polarisation

[Steve Ireland]

>I have NEVER had a dipole lower than 200 feet beat the high horizontals
>or my verticals at distances greater than 200-300 miles.


G'day all

I guess what works best from your particular QTH is what works best - and
predominantly horizontal polarised antennas will work better at some
geographical locations, for both latitude and earth conductivity reasons,
than vertically polarised ones, as happens at my QTH on 160m.

However, what type of polarisation works from one particular QTH on 160m
may not necessarily work so well on 80m - which certainly applies to my QTH. 

I should add that there usually more PRACTICAL reasons than theoretical
ones as to why a particular polarisation of antenna works best at a
particular QTH.

It would be nice if we all had large QTHs like that of my friend Tom W8JI,
where it is possible to create relatively theoretically 'perfect'
horizontally and vertically polarised antenna systems for working 160m DX.
However, even if I could magically move Tom's acreage, towers and antennas
to my location in south western Australia, I doubt that they would perform
in quite the same manner that they do in Georgia.

Over the last five years, on a narrow half acre lot in WA, with gravel soil
and large rock 'floaters', I have used a variety of horizontal and
semi-vertical antennas on 1.8MHz and 3.5MHz.  The biggest earth screen I
could put up owing to space limitations was an elevated screen of 60
radials, ranging from 70' to 30' (most around 50 - 70') in length, spaced
6' apart, with a perimeter wire connected to them.

Various inverted-L antennas, with vertical sections of 60 - 70' were used
over this ground screen on 1.8MHz.  None worked any better than an
inverted-U shaped dipole with the top at 50' at any time - and often were
considerably worse (particularly near sunrise), even on local ground wave
signals.  However, on 80m, inverted-Ls over the ground screen worked 'gang
busters' and generally outplayed my dipoles on DX, except usually at
sunrise, much in the manner described by W4ZV.

Of course, my ground screen was twice the effective size on 80m than it was
on 160m - virtually full sized - and thus was much more efficient on the
former.  As ON4UN says, good verticals usually need lots of space for big
earth screens.

When I upgraded my tower so I could put up an inverted vee at 90', this
outperformed the lower inverted-U dipole by a substantial margin,
particularly in giving a bigger time window at sunrise when long distance
DX was audible.  The inverted vee at 90' is just about the best 160m
antenna I can put up at this QTH, with my space, longitude and earth
conductivity issues.

Unless you have a rural QTH with lots of space, good earth conductivity and
live closer to the poles than the equator, for me a horizontal antenna
(inverted vee/dipole 50 to 140' high) is often a more PRACTICAL and
effective antenna than a compromise vertical system for 160m (i.e.
inverted-L with small ground screen). 

As Mauri I4JMY points out, a dipole of this height can provide 6 dB gain
straight up (very useful at sunrise!!!).  Whilst it may be up to 10 dB down
on a full sized vertical over a proper sized ground screen at really low
angles (up to 15 degrees), it is only 3dB or so down at 30 degrees and very
little down at 45 degrees. Now, an antenna which radiates efficiently all
the way from 30 degrees to 90 degrees is a very useful antenna for DX
working on 160m in my book! 

One day I hope to move somewhere nearby where I can put in a full-sized
ground screen for 1.8MHz.  Maybe then a vertical antenna will mostly
outplay a dipole for me on DX.  However, rest assured I won't take this
'fact' for granted - and would still keep both types of antenna polarisation.

Let's keep an open mind on what works best on 160m - because it depends on
where you live and what space you have available - and what the ionisphere
is doing.

Vy 73,

Steve, VK6VZ


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