Topband: Vertical antennas aren't always best for DX everywhere - the facts
vk6vz at arach.net.au
Sat Nov 24 06:08:40 EST 2018
Hi Frank (and Rick)
Somewhere I have a map of the lines of geomagnetic latitude superimposed on a Mercator projection of the world, but I can’t find it right now. Unlike the ruler-straight lines of conventional latitude, geomagnetic latitude lines wander across the world like a collection of snake tracks.
As a result of how geomagnetic latitude snakes across the globe, a comparison can’t be directly made between similar geomagnetic latitudes in the northern and southern hemispheres – where Tom W8JI lives is probably very different to me in terms of the closeness of his geomagnetic latitude to the electron gyro-frequency. As Carl K9LA points out, the geomagnetic latitude relates to polarization and involves the ordinary and extraordinary waves that propagate through the ionosphere, and how 160m is affected by being close to the electron gyro-frequency.
About 10 to 15 years ago, Carl, Nick Hall-Patch VE7DXR and Bob NM7M (SK) (also a physicist like Carl, as I’m sure you recall) helped Mike VK6HD (SK) and I to understand why our horizontal cloud-warmers outperformed efficient vertical antenna systems in SW WA.
You are quite correct, the Fresnel zone where I live (the mostly far field region where ground gain is developed) has very poor conductivity. And, to repeat your point as this is not as widely known as it should be, poor Fresnel Zone conductivity has very little impact on the performance of horizontally polarized antennas, while having a major impact on vertically polarised ones.
While the Fresnel (far field) zone of my location, is basically rock (granite and ‘coffee rock’), Mike’s final location beside the Kalgan estuary appeared to have much better Fresnel zone conductivity, with less rock than me and, in around half the compass directions, salt water. However, his inverted-L with an 80’ vertical section over 120 buried quarter-wave radials at Kalgan performed only marginally better than our previous attempts at vertical antenna systems did.
On this basis, I came to the conclusion that the dominant problem was likely to be the geomagnetic latitude issue, rather than poor conductivity in the Fresnel zone – which it certainly is also an issue here.
To investigate this further, I sought out the opportunity to operate directly by the sea here with a good vertical antenna. After much paperwork, I managed to get permission to operation from the Cape Leeuwin lighthouse, which is 40m-plus high and on a narrow finger of land surrounded by sea for over 300 degrees.
In a Stew Perry TBDC in the early 2000s, with the assistance of my friend Phil VK6PH, we put up a full-sized quarter-wave wire vertical on the most seaward side of the lighthouse, less than 60 metres from the sea. This was fed against a quarter wave counterpoise and the feeder decoupled with a large ferrite choke to stop common mode effects. On the other side of the lighthouse was an inverted vee half-wave dipole. Both antennas were supported from the lighthouse balcony (at about 40m!) and detuned when not in use. An Yaesu FT-1000MP was used, running less than 100W
Unfortunately conditions were poor during our evening time into North America, but at about three hours before sunrise the 160m band opened into Europe. Right from this point, the vertical was slightly down on the inverted vee by a few dB, but I would always call on the vertical first and then switch onto the inverted vee if I got no response. All the way until just after sunrise, the inverted vee outperformed the vertical, mostly raising the stations who did not hear us on the vertical.
The only time this situation was reversed was when 160m started to go out as the sun started to rise and I had by then switched over to just calling stations on the inverted vee.
After about five minutes of this, the Europeans I could still hear were not coming back to me anymore. Out of curiosity, I switched to the vertical – and found I could still raise a few of them. I recall vividly the last QSO with a CT1 using the vertical about 20 minutes after sunrise, exchanging 559 reports.
The crazy thing is that the vertical appeared to be doing exactly what a dipole is known for doing on 160m in the northern hemisphere in some cases – extending the sunrise opening. However, this was the only time the vertical outperformed the inverted vee.
As far as I know, Mike VK6HD never experienced this phenomenon when he was comparing his inverted-L quarter wave antenna against his inverted vee dipole. However, my vertical antenna was directly adjacent to the sea, surrounded by sea, which may have helped.
The final event was highly interesting, but did not sway me into repeating the experiment the following year when I also operated from the lighthouse in the Stew Perry TBDC.
The fact was the inverted vee had been responsible for 80 to 90 per cent of my QSOs - can’t remember exactly how many – while the vertical had only accounted for three or four.
Mike VK6HD, Phil VK6GX and I are not the only ones to have experienced the “verticals aren’t always best for DX” situation here. About five to ten years ago, I understand a group of German DXers came here and operated in the CQ WW CW (I think).
The group operated from the the Northern Corridor superstation VK6ANC/VK6NC, using a quarter wave vertical on 160m. After disappointing results, one of the ops (Mar DL3DXX, I think) recalled Mike, Phil and I used inverted vees at 90 to 110’ and suspended a inverted vee dipole as high as they could and changed over to using this. My understanding is then they found they could work a much larger amount of DX stations on 160m.
What Steve and Nick VE7DXR were referring to is the geomagnetic latitude in relation to polarization - not ground conductivity.
This involves the ordinary and extraordinary waves that propagate through the ionosphere, and how 160m is affected by being close to the electron gyro-frequency
From: donovanf at starpower.net
Sent: Friday, November 23, 2018 12:56 AM
To: Topband reflector
Subject: Re: Topband: Vertical antennas aren't always best for DX everywhere - the facts
Hi Rick and Steve,
Steve's QTH is almost directly north of the south geomagnetic pole.
His latitude is approximately 32 degrees south geographic latitude
and approximately 43 degrees south geomagnetic latitude. His QTH
is at approximately the same geomagnetic latitude as the Georgia
in the northern hemisphere.
I can't comment on the actual horizontal vs. vertical polarization
experience of topband operators in the Georgia.; however, W8JI lives
in Georgia and his experience with a very high horizontally polarized
dipole was mostly unfavorable compared to his 4-square vertical
array. Georgia probably has reasonably good soil conductivity.
My suspicion is that the soil in the Fresnel zone of Steve's vertical
antennas (the mostly far field region where ground gain is developed)
has very poor conductivity. Poor Fresnel Zone conductivity has very
little impact on the performance of horizontally polarized antennas.
AM broadcast antenna engineers who have worked in VK6 may have
some experience with soil conductivity impacts on the effectiveness
of AM broadcasting antennas in that area.
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: "Steve Ireland" <vk6vz at arach.net.au>, n4is at n4is.com, donovanf at starpower.net, "Topband reflector" <topband at contesting.com>
Cc: "Dave Olean" <k1whs at metrocast.net>
Sent: Thursday, November 22, 2018 3:40:10 PM
Subject: Re: Topband: Vertical antennas aren't always best for DX everywhere - the facts
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.
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
> 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 at n4is.com
> Sent: Saturday, November 17, 2018 8:38 PM
> To: 'Steve Ireland' ; donovanf at 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.
> This email has been checked for viruses by Avast antivirus software.
> Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
More information about the Topband