Holy YMMV. Thanks for your great posting of what most of us didn't know
(I know I didn't). Do you have any numerical data concerning the ground
conductivity in VK6 vs the VK east coast? The conductivity at my
QTH is around 30mS, so obviously you are in an alternative universe
by comparison. I am trying to separate out ground conductivity vs
geomagnetic latitude. Isn't the VK east basically at the same
latitude as VK6? It would be interesting to try a vertical on
the beach on the Indian Ocean in VK6. This would presumably eliminate
the ground conductivity issue, leaving only the geomagnetic stuff.
73
Rick N6RK
On 11/22/2018 1:49 AM, Steve Ireland wrote:
Hi JC
In my experience, here in the southern hemisphere and relatively close
to the equator, I wish that "Vertical TX antenna is the only way to work
DX on topband!"
Unfortunately vertical antennas mostly don't work here well where I am
in south-western WA - there is too much ground loss in the far field and
poor geomagnetic latitude for them.
When I lived in the UK and was G3ZZD (1971 to 1989) , I used verticals,
inverted-Ls and inverted-tees over elevated radials exclusively for
low-band DXing. It was very disappointing to find that when I moved into
the Perth Hills in 1995 and got back on 160m that verticals didn't work
like they did at my previous QTHs in the UK.
Mystified by this situation, I contacted Dr Nick Hall-Patch, a
radio/physics scientist at a university in British Columbia, who
explained the wonders of geomagnetic lat/long to me - and pointed out at
my geomagnetic lat/long a (mainly) vertical polarised antenna might only
break even with a (mainly) horizontal antenna, even if the ground
conductivity was good.
Mike VK6HD, who was my mentor on 160m, had learnt about the favouring of
our location for predominantly horizontal polarisation many years before
- and, after trying a raft of inverted-Ls and various ways of
shunt-loading his tower, settled on using a flat-top dipole or inverted
vee dipole as high in the air as he could get it. Independently, Phil
VK6GX (formerly VK6ABL) went a similar journey to Mike and also settled
an identical philosophy for 160m antennas.
As outlined in my tribute on Mike's QRZ.com page, when Mike moved to his
final QTH, near Albany, on several hectares besides the Kalgan River
estuary, he finally thought he had found a location where a vertical
would work. Over about 18 months, he laid down a full-size broadcast
ground screen of 120 quarter wave radials and put up an inverted-L with
an 80 feet vertical section over it. He compared this very carefully
against an inverted vee dipole at 90', which was detuned/shorted when
the vertical was in use.
Mike then embarked on 18 months of testing - and much to his
disappointment discovered that the inverted-L was mostly up to two 'S'
points down on the inverted vee dipole. The only times the vertical was
better was occasionally over one and half hours before sunrise - and
similarly it could sometimes be better over one a half hours after sunset.
The good news is once in a blue moon the vertical would work better than
the dipole on long distance DX - and enabled Mike to work P4 (Aruba) and
HC.
Almost entirely the rest of Mike's 260+ countries on 160m were worked on
flat-top or inverted vee dipoles.
After another year or so, Mike quietly took the inverted-L down - and
concentrated instead on improving his 160m reception through the use of
Beverage antennas.
For many years, Mike and I were treated by several knowledgeable 160m
DXers as being either incompetent or deluded about a simple horizontal
cloud warmer being better than a vertical in south-western WA. I used
to get angry about it, but Mike (who was older and wiser) would just
laugh and say let those in the rest of the world have their own beliefs
about what actually happens where we live.
If the books in English on 160m antennas and operating had been written
in VK6, rather than in high latitude USA and Europe, they would say very
different things about verticals, along the lines of: "Don't torture
yourself." ;-) Note also that verticals seem to work just fine in the
rest of Australia on 160m, but not in relatively coastal south-western VK6
Practically for me, verticals of all kinds are occasionally useful at
this QTH in working middle distances around 1,000 to 5,000 km, such as
in the western Pacific. Later this year, I'll carry out the switching
arrangements so I can use my 160m doublet as a top-loaded vertical, but
I'm not expecting much in the way of good results, except at these
distances (in which I've already just about worked all the countries
there is ;-)).
By the way, I have a ground screen of over 30 x 30m radials and a K2AV
counterpoise over them - for all the good they (don't) do me. If I was
back in Kent as G3ZZD they would do very well for me.
Vy 73
Steve, VK6VZ (also G3ZZD and VY2LF)
-----Original Message----- From: n4is@n4is.com
Sent: Saturday, November 17, 2018 8:38 PM
To: 'Steve Ireland' ; donovanf@starpower.net ; 'Topband reflector'
Cc: 'Dave Olean'
Subject: RE: Topband: Vertical and horizontal polarized antennas in the
same space (was Propagation improves from VK6 into Europe)
Hi Steve.
You are 100 % right, the V works like a top hat for a vertical TX antenna.
I it simple to detune any vertical TX antenna. Vertical TX antenna is
the only way to work DX on topband!
You may ask about the inverted V or low dipole, they are not 100%
horizontal, actually they are 50% horizontal on the broadside and 50%
vertical along the wire.
Ground reflects horizontal signals -1, it means 180 degree out of phase,
and the reflected signal cancels the arriving signal, The Arriving
signal is maximum only near 1 1/2 wave high above ground 750ft!!!.
The vertical reflected signal has +1 and add to the arriving signal
producing gain, ground gain.
Detuning a TX antenna is like a LC circuit, you need high impedance
between the antenna and the ground. The UNIPOLE or cage antenna works
very well to detune grounded towers up to 30 db, and it is easy to feed
with 200 ohms, becoming a very large broadband antenna. Isolated towers
or inverted V is the same, they need high isolation from ground.
I sed the same configuration for over 20 years, the open line works very
well 80 - 10m.
Regards
JC
M4IS
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