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November 2002

Beechlog
 
The on-line magazine of the Burnham Beeches Radio Club.

Blog title

November 2002 Edition

Contents

Welcome to the November BeechLog!

A follow up from the talk about Weather satellites last October
How to make cheap wire aerials
Some photos from 2002
Why we all have Broadband
This months Useful Links.

Welcome to the November edition of BeechLog.

Well, it's that time of the year again. And as I write this, I am in almost exactly the same position as this time last year, i.e. unemployed. Actually I might not be, for although I was made redundant last Tuesday, the Jobcentre told me that my dismissal letter did not breakdown the 'compensation' from my ex-employer in sufficient detail, and so I was not allowed to 'sign-on'.

So I'm not counted in any government figures, no wonder they are still so low. Anyway here I am again, just before Christmas, with no income. It's funny how this seems to happen at this time of the year. It's all damp and rainy outside, so I'm cooped up in here, writing BeechLog. At least you might get it on time!

Roger GØHZK, Editor


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Weather Satellites

Keith Holland, G3MCD, gave the club a talk on 21st October about remote imaging and receiving pictures from weather satellites.

Weather satellites fall into two main groups (1) polar orbiting at about 500 miles up (on 137-138MHz) and (2) geostationary satellites over the equator at about 25000 miles up (on 1700 MHz).

Part of his talk was a demo, and an infrared picture was taken from the polar orbiting American satellite NOAA17 on 137.62MHz as it travelled over Europe at 9.23pm. Keith used an indoor crossed dipole, with a Timestep receiver and decoded the signal with the program WXSat onto a laptop.

There was a lot of cloud over Europe, but we managed to get infrared pictures of northern Holland and The Gulf of Finland with the area around Helsinki plus the Baltic Sea down to The Gulf of Gdansk.

Keith has since extracted part of the pass and processed it so that it shows up a little better.

NOAA17 image This is an infrared picture of the Gulf of Finland and the area around Helsinki with the Gulf of Gdansk in the south.

A summary of the various satellites, their frequencies and pass times was given out at the meeting. If you missed the meeting and would like a copy send Keith an e-mail at:

KOHolland@aol.com

Keith is a retired engineer and the Deputy Manager for the RSGB responsible for London. He has been a member of the Remote Imaging Group (RIG) since the mid eighties and he runs a help line for people setting up weather satellite systems.

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Cheap wire aerials.

During the HF convention I attended a 'lecture' about getting together a cheap HF station. One of the topics was aerials - how to get something up at minimum cost.

When I read articles about wire aerials, it always seems that the writers 'small' garden is a couple of hundred feet long, with convenient tall trees at one end, and the three storey house at the other! Reading the articles, they describe wire lengths of 161.5 feet or some critical figure - with the suggestion that any slight change and the aerial ceases to work.

Of course, in practice this is far from the case. Any bit of wire will radiate if you can get the RF into it. Of course, it may not be very efficient, but then a 50% efficiency means only a loss of half an S point over a perfect radiator. Probably the height has the greatest effect - the lower the bit of wire, the higher the angle of radiation and you cut the chances of getting a good signal into the other side of the earth.

Since I passed the dreaded Morse test, I have played about with wire aerials from time to time. I've got lots of wire, but it's only 7/0.2mm stranded stuff that breaks as soon as the wind blows. So I only get a few days before the aerial is down. Last attempt was a wire to work that Dxpedition to some island off East Africa, can't remember the name, but unfortunately the feeder got mixed up in the Flymo - ah well.

I'm not too bothered about DX, just as well because DX is not too bothered about me. But a few years ago I wanted to talk to some friends up north, so I fashioned a forty metre dipole. This is supposed to be 66 foot long, so I cut the length right and strung it up in my 28 foot garden. Yes, it wasn't straight, and folded around a bit, but the most important thing was that it worked well. Signals from all over the UK were good, and I got impressive reports from the people I spoke to. It worked fine for Europe, and I even had a few contacts into the USA before it fell down.

It just so happened that one of the chaps up north managed to set up a station on a Trinity House vessel that was on a mission to deliver supplies to the lighthouses around the Shetlands and Orkneys. This brave man was winched down from a helicopter onto numerous lighthouses, where he operated using a forty and eight metre 'handheld' connected to a bit of wire that he dangled over the edge of the helicopter platform. No time to tune up this 'aerial', but the upside down ground plane hanging over the North Sea radiated the two watts far and wide.

To make the contacts on eighty, I had to do something about my aerial. My tuner couldn't really manage the task on the forty metre dipole, and folding the 132 feet of an eighty metre version into my 28 foot garden seemed to be a silly idea. So all I did was increase the length of the dipole by soldering a few extra feet on each end. This did the job of allowing the tuner to cope, and so I made those eighty metre contacts, without upsetting the performance on forty.

So ignoring the changes in radiation pattern, what do the figures look like? I've made a few calculations. Here is a basic forty metre dipole, 20.56 metres long, fed by 20 metres of 300 ohm twin feeder. This connects to a 1:1 balun, and then to the radio. The aerial height is 10 metres.

This works out as a purely resistive 74 ohms at the dipole centre, and the feeder increases this slightly to a resistive 78 ohms. So there's a 1.5 SWR at the radio. The system efficiency is about 92%, a loss of less that half a decibel.

On 3.7 megs, this system has a resistance of 6.6 ohms, and a reactance of 100 ohms. At the dipole centre this is 22.6/-1068 ohms. Oh dear. Once you have coped with the SWR of 56:1, you have an efficiency of 17%, nearly an 8 dB loss. But that's only one and a bit S points, but matching it is the big problem.

Looking at this problem, the first thing to notice is the length of the twin feeder - it's about half a wavelength on forty, but a quarter wavelength on eighty. Half a wavelength is fine - it simply presents the same low impedance at each end. But a quarter wavelength has the opposite effect - a high impedance is changed to low, and vice-versa.

So a simple solution is to change the feeder length. Reducing this to 14 metres will reduce the SWR to 19, and increase the efficiency to 25%. But the match of the feeder to the dipole is still not good, so to improve this simply increase the dipole length to 25 metres.

This makes a surprising difference. On 3.7MHz we now have an SWR of 8 at the radio, and when matched an efficiency of 42%. Switching back to forty, the SWR is still 1.4, and the efficiency has risen to 93%.

This aerial also matches well on twenty, but is a pig on fifteen and ten. But it's not bad for a simple bit of wire. There may be a problem with RF in the shack, you could stick the balun outside and feed it with some coax. Simply putting 5 metres of coax between the radio and the balun will not alter the performance much, on forty we will lose about 5%, and on eighty about 8%, but the matching on both bands will be much the same.

The configuration of this aerial is rather like the infamous G5RV, although it is optimised for forty and eighty, and about twenty foot shorter. The function of the coax is just to reduce RF in the shack, and it reduces efficiency by just a little. But contrary to what some people might say, it's worth playing about with these wire aerials.

There are other variables, such as aerial layout, height, and proximity effects. Personally I can't see how I can get an aerial up at 10 metres, let alone three or four times this height which would seem more appropriate for DX.

I suppose much the same thing can be applied to vertical aerials. While it would be nice to erect one of those Titanex top band jobs, we don't all have the space for guying such a beast. And the neighbours may well take exception the 130-foot height of the things. Why, if one of those got blown over, it would stretch across about 10 neighbours gardens. You'd have to wait 'till they all went on holiday together to do a spot of maintenance!

Short verticals usually have all sorts of gizmos up and down the length, lumps here, and spikes there. But by careful calculation of feeder length and the height of the thing, it should be possible to work on two or three bands with a straight bit of wire or tubing and a decent ATU.

You can calculate this stuff fairly easily, but there is software that brings all the necessary formulae together. There's a guy called Reg who has a web site full of such programs, I'll link to it at the bottom of BeechLog.

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Some photos from 2002

Quite a lot has been happening to BBRC during the past year. Despite our small membership, we have had many interesting meetings, manned the GB50 special event station, the HF Convention, the McMichael Rally, run two Foundation Licence courses, held the RAE, and much more. here are some pictures taken through 2002.

Johns antenna HF Convention GB50 Foundation Course

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Why we all have Broadband

From time to time there are reports in the press about the growth of internet connectivity in the UK and elsewhere. You know the sort of thing, "40% of UK consumers connected to the internet" or "67% of Danish families have broadband". The accuracy of such figures are not questioned, but having worked in a marketing department I am well aware of how figures are invented to create impressions, reality is usually different.

I have recently been reading about the uptake of broadband in the UK. Usually we are told that we are far behind everyone else in the world, but I think it all depends on how you define the term 'broadband'. I find it hard to believe that UK families are much different from those anywhere else in the western world - and many families I know are unconcerned with whatever the net offers, they are too busy watching soaps and (un)reality programs on the telly.

The industry is partially aware of this, a few days ago I read a report on the failure of an ISP, partly blaming this on the lack of 'content' provided by the ISP. Which suggests to me that 'the internet' is not what people want from their connection. A couple of years ago, before the bubble burst, we were told that we should expect to use the internet for 'entertainment', and what they meant by this was that it was going to be something like television, with us public folk feeding in 16-digit credit card numbers to see films on demand.

Well, this hasn't happened, but we were offered numerous opportunities to feed in those 16-digit numbers. Unfortunately the businesses concerned didn't do their homework - they didn't think about where we were going to find this money - and so there were collapses all round.

The fact that the 'entertainment' side was not going to happen should have been obvious to those suggesting it. The internet we have today is simply not suitable for this. It was never designed to deliver such content. Even the broadband connections that some people have are not suitable, for while their quoted bandwidth is capable of delivering television, their bandwidth is shared with perhaps 25 or 50 others. And if anyone else is watching internet TV at the same time, bang goes the quality. The size of the pipes needed to deliver, say, 500kbit/s TV to all and sundry continuously, would be a couple of orders of magnitude greater than they currently are.

The only way this can work is to have the servers that deliver the television located at the other end of your own broadband pipe, i.e. on your ISPs premises. This way, the internet is not involved at all, and only the ISP has to beef up its pipes and delivery system. There's another name for this: cable TV! In fact cable TV is much more suited, as this is exactly what it is designed to do. However the cable TV companies in the UK are all losing money, and always have been. So the likelihood of 'entertainment' over the internet being viable just isn't on.

Anyway, back to the internet as we know it. Recently I had the 'pleasure' of setting up a connection to an ISP for someone non-technical. This person had already tried, using the CD supplied, and had failed. She had phoned the helpline, who, after extracting five pounds worth on telephone time, told her that TCP/IP needed to be re- installed on her PC.

Well, it turned out that the ISP was BTOpenworld. This is a large outfit, as you may expect, and I thought that these people ought to know their stuff. However, having known a number of technical types who were exasperated by this ISP, I guessed that the problem was most likely to be with BT rather than the PC, and so armed with numerous Windows setup disks, off I went to sort out the problem.

Now setting up a dialup connection to the net is very simple. I first tried the ISP I use for Beechlog, which meant entering a phone number, username and password, into the Windows DUN dialog. In two minutes I was connected to the net. So there was nothing wrong with her TCP/IP installation. Next I tried the BT pay-as-you-go service, no problems at all, apart from the slowness of BT's network compared with my Beechlog ISP.

So in went the BTOpenworld CD, and off we went. Now, setting up a dialup connection is very simple, but BT has made this process as complex as it is possible. It was no wonder that my friend had given up. Part of the problem is that the money has to be paid to two parts of BT - the ISP and the telephone company. Initially the CD connects you to the ISP, where numerous forms are filled in. When it's got so far, you are routed to the telephone company, to fill in more forms. When that bit was complete, you are left in the lurch! Nothing routes you back to the ISP web site, where you need to fill in more stuff, although to be fair to BT the browser window was still open.

I figured this out, and we were in business. Well nearly, because it asked for the go- ahead to activate the service, and unfortunately the tick box was hidden off-screen.

So what had gone wrong when my friend had tried to set this up? Well, my opinion is that it was solely down to BT's web designers. The process opened unsuitably sized windows, hiding essential information. Then the routing from one site to another was very poorly handled. Both sites operated in isolation from one another. The types of services offered on both sites was confusing, names and jargon were inconsistent, so at the end we weren't quite sure whether we had signed up for the right service!

What annoyed me is that all this could have been so much easier. All that was needed were answers to four basic questions: What username would you like? What password would you like? Which BTOpenworld service do you want? How do you want to pay? This jumping between web sites is quite unnecessary; all the necessary data could have been passed between the web sites in the background. Instead of the 45 minutes we took to set this connection up, it could have been 10 minutes. Bah.

Of course, being a technical bloke, things are easier for me. I reckon I could sort out broadband in a few moments. But unfortunately, although my phone supplier is called "Telewest Broadband", that latter word is exactly what they cannot supply in Slough. I keep intending to remind them of this every time I phone them up to pay my bill, but so far I've let them off. I suppose I could get BT reconnected ("Every day, 400,000 people come back to BT" or whatever they say). I do have BT wiring, although since I had new windows installed, the wires are just dangling outside the window. I must sort this out. If I was reconnected, and didn't use the phone at all, would I get the low use discount? And where would the router go?

Anyway a quick look at the BT web page reveals all. Firstly a phone line. Well, clicking on the link does not actually give a price! It refers me to their on-line price list, Section 1, Part 2, subsection 3. Nice and convenient. Anyway five pages later I find out that BT charge approximately £75 to install a domestic line. The ADSL install charge is only £30 until the end of the year, and the router and filters about £80. So that's about £185 to install BT broadband. Running costs? About £26 on top of the monthly BT phone bill.

So for the first year, BT broadband will cost me roughly £500, assuming I ditch the Telewest 'Broadband' phone and dialup internet service. If Telewest lived up to their name in Slough, it would cost only £25 installation, and £25 per month, totalling 'only' £325.

Ignoring the installation costs, this represents a little over twice as much as I pay now for unmetered dialup. Whether this is value for money is a personal matter. I find my current dialup service is pretty good, it's reliable and fast enough for what I get up to. Obviously I can't really download movies, but then I'm not going to sit watching them on this cheap 14" PC monitor. I don't even download music, legal or otherwise, especially not the sort that times out after a while. Big downloads are not on either, but I can live without those.

To me this market still seems very immature. We put up with poor service and system failures, and use PCs with complex and unreliable operating systems. I'm not even sure whether our IP networking protocol is the right one, it was invented a long time ago when the though of everyone and their fridge being connected was inconceivable (there's another thing, where are the online fridges predicted a few years ago?).

I'm not saying that all these things won't happen sometime in the future. But as far as most people are concerned, they are tied to monopolies. If this is the only way, I would prefer internet connectivity to be handled by a different monopoly, and not tied to a phone company. But the problem will be one of finance. Who will pay for a national fibre network? And will subscribers pay enough to maintain it? I suppose that in the meantime we will have to but up with the current bodges. Oh well.

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Internet links

Various programs for calculating aerial sizes and properties can be found on Reg G4FGQs web site. These are DOS programs, but run easily on an Windows PC.

Where does 'CQ' and '73' come from? Some information and arguments can be found on the W5WWW website.

The Satscape weather satellite program.

Here are the amazing pictures taken by the IKONOS satellite.

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Copyright and Technical Stuff.

BeechLog is Copyright Burnham Beeches Radio Club 2002.
Copyright of individual articles and pictures remains with the authors.

Any opinions inside this issue of BeechLog are those of the authors, and must not be assumed to be also of the BBRC.

BeechLog is written in XHTML version 1.0 and contains a few differences from the last issues. However different browsers handle XHTML and the associated style sheets in different ways, so there is the possibility that you may not see BeechLog as I intended! If there is anything that seems amiss, please let me know:
Roger GØHZK, Editor