Friday, 7 October 2016

VHF from a fairly poor QTH

There are many amateurs who have to make do with a less-than-perfect QTH. Like me for instance. But that is no reason to give up.

This location was chosen for reasons which did not include its radio potential. Sure I knew that it is, more or less, the highest house in the village. However, it was chosen mainly because of its cheapness, its suitability for being gutted and rebuilt, and the scenery.


Once every room in the house was altered, extensions and garages built, and everything was finished I could turn my mind to radio. OK, I now knew about laying drains and driving diggers, but I had left the radio for later. It turns out that this is not a great VHF location ... or is it?

First the bad news.

If you were to come here and plonk down a 2m colinear you would conclude that it does not have much going for it. Judged on the standards of normal conditions or mild tropospheric enhancement it does not do well. Years of working during the RSGB "National" Activity Contests, and the Nordic Activity Contests mean I know now what to expect. Mostly silence.

The site is fairly open to the East and not bad to the North. To the West are the Border Hills, part of the "Scottish Lowlands", a series of hills around 1000 to 1500 metres high stretching from here about 150km to the West Coast (EDIT OK, that was  a bit generous, the Lowlands have eleven peaks over 700m, and the highest is less than 850m , but bumpy nevertheless). To the South is a large headland with the bulk of The Cheviot behind, 815m high towering over our measly 60m. So to the South for sure, there is a big obstacle.

The main feature to the East is the North Sea, stretching away about 500km and bounded successively from North East to South by Norway, Sweden, Denmark, Germany, Netherlands, Belgium and England. That ought to help with sea paths but the ground rises from here to the coast, only 3km away. I cannot complain, as once you reach the coast there are some very nice cliffs. So if I can get over the rise to the cliffs I am well away in that direction.

The North is not as bad as it might be. We are in a dip and to the North of us is the Eastern Extension of the Lammermuir Hills, succeeded to the North West by the Pentland Hills so I cannot hear anyone in Edinburgh 80km away, nor in fact in Dunbar about 30km away. But once past these obstacles the path to the North is not bad and I do fairly well there, as the Scottish Highlands are rendered invisible by the curvature of the Earth. To the North I am impeded mainly by the fact that there is almost nobody there.

Being in a dip in the hills means that local stations are few to non-existent. For example I struggle to work one station due South (G3KML) 11km away in Berwick upon Tweed. Kelso I can just about make, reaching GM6ZFI 34km away to the South West only because Doug uses an 8 element beam pointed directly at me.

It would be easy to conclude that this is a poor location for VHF and give up. But you may have noticed that I did not give up. Or at least I have not given up yet.

During normal tropospheric conditions I struggle, for instance during contests. I may hear one or two stations from the West Coast, a couple in Fife to the North and one or two on hills in Durham or Northumberland to the South. And that is it for "locals". I do not enter these contests, not just because I am not a competitive person, but also because I have almost nobody to work. I hear of stations in the South East of England who can work 100 local stations, whereas within a 100km radius I might have 7.

So how do I do with stations further away? Thanks to Cheviot, the Cheviot Chain and then the Pennines, I find it very difficult to work anywhere in an arc from South East towards the Netherlands to due South about as far as the Isle of Wight. That must cover almost half of the VHF stations in the UK. I can get to certain places further West, such as Lancashire, the tip of West Yorkshire and then Wales, Devon and Cornwall. The Border Hills more or less cut off South West Scotland and Northern Ireland. Not great coverage for a contest if it happens under normal conditions.

The solutions which many operators use involve bigger antennas, taller masts and more powerful linear amplifiers and preamps. I would rather use guile than brute force.

So what do I do about it?

I have my VHF fall back position. I just do not do much standard tropo; I concentrate on what used to be called "the esoteric modes" instead. I have checked it out and my horizon has hills in every direction if you look horizontally. If you looked along the booms of my beams you would see hills for the full 360 degree turn. If you angled the beams up 1 degree (apart from spoiling any chance of working tropo DX) you would still find hills all the way from South East to West to North. It is not until you aimed the beam up 2 degrees that you would find a clear horizon. Not great for DX? Well, not for tropo maybe.

The methods of VHF propagation I use more are tropospheric ducting, ionoscatter, sporadic E, meteor scatter, aurora and a continuing list of less well used methods. I have not tried earth- moon- earth or satellites yet but they would also be possibilities. These modes all work surprisingly well without being fired exactly horizontally. With standard tropospheric propagation your success depends crucially on a good horizontal takeoff, but these other methods are different.

After spending paragraphs telling you why this place is hopeless for VHF, I have to say that for the other methods of propagation it is really very well sited. I could moan that the glass is half empty, but I rejoice in the fact that it is also half full. So a few points arise.

Point 1: Tropo ducting is different

Unlike normal tropo propagation, tropospheric ducting is tolerant of me being in a dip. It is fairly rare and depends on bending of radio signals in the troposphere, so it is a weather effect. Radio signals normally pass through the atmosphere more or less unaffected, spreading out as they do so. Under certain conditions, when the weather systems produce a certain pattern of air density, the signals can be confined to a layer close to the ground. This has the effect of not only keeping the signals low, but concentrating them in certain directions by keeping them inside the duct. The usual rules for path losses do not work as the signal is not moving out in all directions in to free space.

OK, this effect is fairly rare. You usually find it on a still dry day, with similar weather conditions all the way between you and the stations you are hearing. Typically this is caused by a high pressure weather system, slow moving, allowing the necessary conditions to build up. High pressure of itself helps to produce tropospheric enhancements, but it will not usually form a duct. This is where my location does help. Tropospheric ducts often form over water and me being near the North Sea is a big factor. the influence of the North Sea can be seen in the results on 2m on 5 June 2016 (normal activity in that direction would be zero) ...
As usual, click on the photo enlarge if necessary.

In reality the duct only covered small areas of Europe at any one time, but over a day it has moved around to cover various parts of Belgium, Netherlands and Germany. Ducting can be very pronounced on 70cms, sadly a band on which I am not currently active, 2m and also sometimes on 4m. On the same day, 5 June 2016 there was ducting on 4m too:-
I worked two stations in IO94 square and one in IO75, both locations difficult to reach due directly due to my nearby hills. The effect of the duct has been likened to "bending" the signals and though I do not want to take that idea too far, it is a useful way to consider it. Whilst normal tropo enhancement has the ability to gently bend the signals towards the earth, it is nothing like as effective as a duct and the results do not have such a marked effect.

Ducts rarely affect other bands. They can be very tight, sometimes only affecting one or two stations and sometimes even more annoyingly, one or two beacons. Signals can be quite strong.

I accept that ducts are rare, but they are very useful for stations like mine where there is a sea or coastal path and they are very tolerant of the dip I am located in. I probably see good ducting three or four times per year and signals are loud enough to be easily worked with my modest station.

I hope that I have made the point that while tropo lets me down thanks to the hills, ducts are a particular type of tropo which works well here.

Point 2: Using the ionosphere is different again

Ionoscatter and sporadic E are the next modes and I think any reader of this blog already knows how they work. Basically a layer in the ionosphere reflects (or partially refracts and reflects) or scatters the signal back to earth. On the face of it (and as shown in hundreds of text book illustrations which are WRONG) we might think that as we are reflecting our signal off an upper layer of the atmosphere we should direct the signal upwards. This may or may not work, but the object of working dx is to use a layer of the ionosphere above the mid point between you and the most distant station you can reach. And the geometry of this suggests that the best dx will result if you beam horizontally. So that sounds just as bad as standard tropo for me, located as I am in a dip in the land. Horizontal for me is straight into the headland.

Thankfully it does not work like that. Whereas tropo requires horizontal takeoff for almost all distances, iono and Es only require it for the very, very, very longest distances. In real operating situations, given the distances, the patch of ionosphere you are firing at from your location will be reached (thanks to free space propagation) This will result in you reaching the patch you want even if you are a degree or two out. And it only takes two degrees to get past all my local obstructions.

The scenario is much like this (though I am simplifying greatly). Fail to reach horizontal or very near it on tropo and you have lost a portion of your take-off horizon (tropo ducting is different as the signal is confined or "bent"). By contrast, fail to reach horizontal on iono or Es and you lose a bit of signal at the far end, nothing more.

Let me give an example. As I say I can hardly work G3KML, 11km, due to the hills. That direction is blank for normal tropo. It is blank all the way down through England to the coast at JO00 square. I have never worked JO00 square by tropo, and all points in between are very difficult. The hills screen me completely. Here is the same direction in Es on 4m ..
You might think that the same hills would cut out the signal near the horizontal to reach IS0AWZ and IS0GRB in JM49 square along the same bearing. Clearly not. The geometry is complex but the easiest way to put it is this - to work JO00 square involves getting the signal at ground level there, whereas with Iono and Es the signal is passing over JO00 at somewhere near 100km above ground - which is a lot easier to do when you have a socking great hill at the bottom of your garden.

I cannot easily work anywhere along that line into England, but I can get over the hills and let the expanding signal front reach the ionosphere beyond England.

It is almost like an HF skip zone, all the way down inside the normal tropo range. Instead of the HF signal never reaching those areas, my VHF signal could in theory reach England but cannot due to the shadow of the hills which are very near me.

JM49 square used in this example is just on the theoretical maximum distance for a single hop Es path, 2021km. OK, on the day this might have been a double hop path (but I doubt it). Anyway, a double hop makes the path even easier as the angle of departure would be higher. Careful calculation here suggests the optimal angle of elevation for the single hop path to JM49 is 1 degree, which I can probably just about do. But it is not zero degrees. I know I cannot reach zero degrees elevation. at one degree and I suffer on tropo accordingly, whereas 1 degree gets me great distances on Es.

What I am trying to say here is that in my book there is no such thing as a bad VHF location. There may be poor locations for normal tropo, which might be fine for pretty distant contacts using other methods of propagation. And yes, zero degrees elevation might get a bit further than the 2000km which 1 degree gets, but not much. A better site is always a better site, but what is practical might be greater if you do not limit yourself to tropo contacts.

Point 3: Meteor Scatter and Aurora are new worlds

The same approach works for meteor scatter and aurora. There you are relying on the signals being scattered by ions (and in the case of large meteors, ionised layers) in the ionosphere. And handily both these methods occur at similar heights to Es, so the ranges are similar (though the signals are weaker, so it is harder to reach the extreme distances). The WSJT software many of us use actually gives elevations figures, all worked out for us. For example, I have little difficulty working Henning, OZ1JXY almost every Saturday on meteor scatter. Hardly surprising I can get over the rising ground towards the cliffs in his direction, as the optimum elevation is 12 degrees! And, meteor scatter is effective every day, and during the periodic showers, can be very effective.

In practice I find that for meteor scatter in the practical ranges I can work from here, no hills cause me any problems at all. I have never worked anybody below about 4 degrees elevation, so the hills are irrelevant. Maybe if I ran more power and was trying to reach the very edge of my possible range it would play at part, but not yet. The same applies to aurora, which almost always involves beaming North anyway.
Does the above QSO wheel, all worked on 70Mhz SSB on 17 March 2015, look like a man bothered by bad take off to the South? They were all worked with the beam pointing North with the help of auroral scatter. The hills make little difference to aurora if you are located as far North as me. If you are located too far to the south you do not get to hear so many events and hills and the curvature of the Earth start getting in the way.

4. Even if these do not work for you, there are other possibilities

For earth- moon- earth and satellite work, if I ever do any, my one to two degree penalty will not make much difference, except, once again, at the very extreme ends of potential range.

And if, for example, you are too far South for much aurora activity, Trans Equatorial Propagation might be your saviour. Once again, strict horizontal take off is not absolutely necessary. 

Conclusions

So here is what I find. I cannot get out very well on tropo and my success in monthly contests is limited to the point of making them impossible to enter. I could get over that to some extent by putting up bigger antennas and taller masts. You can get software which shows what you need to do (to reach parts of Yorkshire, for example, a 150m mast would do the trick from here). But any improvements to the antennas and masts would help to some extent. I am not going to do any of that.

I do know that using the less popular methods of propagation I can reach really remarkable distances with the limitations I have. 1 or 2 degrees elevation (enforced on me by the surrounding hills) is not really a problem. I do not raise the antennas, I just let the hills have their share and get over it in more senses than one. 1 or 2 degrees are punishing on tropo, but insignificant in the geometry of the other methods.

So if you leave the rather silly idea that surrounding hills are the only factor, then being near the sea for ducting, a reasonably rare square for Es, fairly far North in UK terms for aurora, and a nice quiet spot for meteor scatter all add up to quite a fair location after all. Yes, a huge mountain right at the bottom of your garden will be a tougher nut to crack, but a hill on the horizon may not be such a problem, thanks to the curvature of the Earth and radio's kind property of spreading out into three dimensional free space.

Contests? Who needs them?

Anyone who thinks that a VHF contest run under normal tropo conditions gives any indication of the suitability of a site for VHF work is crazy. UK Activity Contests are a measure of the depth of the pockets of the individuals who buy bigger and bigger towers and linears. While these folk are busy perfecting their stations for the scalp-hunting season, their money is mostly wasted when it comes to the modes I hold so dear.

If you live down a hole then my advice is to save your money and try the other methods. You could be in for a surprise.

Key point: don't give up just because you don't hear many repeaters. In fact, try harder.

73

Jim
GM4FVM
P.S. Thank you all for quite a few emails about this. I am not talking about contests in general, but rather about contests not being a good measure of a VHF site's potential. Some of my best friends are contesters. I am happy to take all the squares I work during contests. Contests are good, I am saying that my lack of success in them does not mean I cannot work on VHF.

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