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Page last updated on:
Wednesday, November 10, 2010
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Gas Mantles and Amateur RadioHarry Heap, G5HF, was first licenced as 2BZZ in 1932. In this article he tells how he got started As far as I can remember, I started life as a small boy. We lived near Wimbledon Common, which has numerous ponds where, in winter, we skated and when warm enough I sailed my model boats with friends- sailing boats, electric boats and Toc-Tocboats (remember them?). It was the mid 1920s and I was reading several books about the sea battles of the Great War, the Battle of Jutland, the Battle of the Falklands and two or three more. Looking back at those battles now, I feel that they must have been horrendous, as many thousands were killed and injured in terrible conditions. But to a small boy they looked very exciting and great fun! I was 8 or 9 at the time. I used to day-dream of being able in some magical way to control my model boats so that we could have model sea battles on Wimbledon Common, with guns, smoke, torpedoes and great sinkings. Then about 1928 I saw an article in Boys Own Paper entitled "How to build a wireless controlled model boat." Eureka!! This was it! I assumed that the article described the state of the art on wireless, but I now see that the circuits were the same as Marconi used thirty years earlier, but the advantage was you could make almost all the components needed. The transmitter was spark, using a Ford ignition coil, and the receiver used a coherer, which they said could be purchased from Gamages for five shillings. The coils were made from the inside of toilet rolls dipped in paraffin wax and the condensers (capacitors to the young) were made from 2lb jam jars lined inside and out with tinfoil. This was REAL tinfoil stripped from the insides of tea chests and beautiful material to handle and solder. No araldite then, so we used Secotine, a glue made from animal bones, very smelly, but a good sticker. The Ford coil was a wonderful construction, being mounted in a wooden box with dovetailed corners and filled with paraffin wax. Almost bomb-proof and fitted with a trembler on one end, so all you needed was a 6 volt battery. I used a 12 volt battery and got sparks up to 2 inches long with needle spark gaps. The next problem was how to make a coherer. I couldn't afford 5 shillings to buy one as my pocket money was only about 2 pence per week, and it all went on sweets. So I said to my Dad, "How do I get a coherer and one or two other bits, like relays?" He was manager of a gas mantle factory in Wandsworth and he took me there to get help from the chief engineer and the chief chemist, who were friends of mine as I used to spend time there during school holidays ("We must be nice to him. He's the boss's son"). The engineer machined up a piece of ebonite to make a cup-shaped coherer and fitted it onto an old bell for a tapper. The next problem-was to get iron filings. Every chemical laboratory had a bottle of "Iron Filings" but this material was made chemically pure by reducing a chemical salt to pure iron but this was much too fine for a coherer. So the engineer said he would file some iron in his workshop. The workshops in those days were very simple as they dealt with either steam or gas engines. so the main tools were the blow-torch and the sledge hammer. but as steel and iron were the main materials the whole place was saturated in oil and grease. Taking an oily file and an oily piece of steel, the engineer produced some beautiful filings liberally coated with oil the chemist degreased them with Ether. Why Ether? I'll explain. Gas mantles are made from Ramie fibre from China. This is a very fine, strong fibre like a silky kind of cotton and very strong. The mantles were made on knitting machines in many shapes, domes, tubes and the Max Miller. This last one was so- called because Max Miller used to describe a pretty girl as "A little bit, some more and then not quite so much" and this described the mantle perfectly! The knitted mantles were then attached to a clay ring by tying and then dipped in Thorium Nitrate solution. Thorium is radio-active but nobody bothered in those days and although the whole factory was thick in Thorium dust nobody seemed to suffer. My Dad was handling Thorium all his life and lived to 93. He said radiation was good for you! There is no truth in the rumour that the cemetries in Wandsworth glow in the dark'. Next the mantles were tired on high pressure gas flames to burn off the fibre and convert the Thorium Nitrate into Thorium Oxide ash, which took up the same shape as the original knitted fibre. Thoria ash has the same strength as cigarette ash and is very fragile, so the finished mantle could not be despatched to all countries of the World and parts of Glasgow. I mention Glasgow because huge quantities of mantles were purchased by the occupants of the tenement buildings where gas lighting was widely used. as it provided heat as well as light. In those days (perhaps even today) it was customary to drink a glass of whisky on Saturday night and they found by bubbling coal gas (containing 30-40% carbon monoxide) through the whisky, the drinker got an extra kick! However, in order to bubble gas through the liquid it was necessary to break the mantle and fit a new one later. Hence good business for Dad. To protect the mantle during transit, it was dipped in Nuskin which mothers used to treat small cuts and abrasions on their children. It stung like hell when put on an open wound, but in a few seconds it left a film over the wound and kept out the dirt. Nuskin is a solution of Cellulose Nitrate in Ether. Cellulose Nitrate is also called Guncotton, because it was used as a propellant in the guns of the Great War. Today the police would clear a radius of 5 miles if you reported a tank of 50,000 gallons of Guncotton in Ether; but in those days no one bothered. Father thought it might be a bit dangerous in a factory of 500 girls, so he put it in a little wooden shed. In the 25 years it was there, I never heard of any trouble, though they did call the Fire Brigade to do a test. They put some Ether in a shallow tray, set it alight and asked the Fire Brigade to put it out. Water was no use at all, so they tried foam which appeared to smother the fire, but in a few seconds the Ether pushed its way through the foam and re-ignited. When the foam finally ran out, the Fire Brigade said "Sorry, we can't help you," so they packed up and went home. So, we used Ether to de-grease the iron filings and a better degreasant you couldn't find because Ether dissolves almost anything! One day a small procession headed for Wimbledon Common - the chief engineer, the chief chemist and myself with Father tagging along for a laugh We set the spark transmitter and the boat on the bank, degreased the filings and tested the system. It worked OK. The boat tiller was kept central by a spring and solenoids were fitted to both sides to attract a soft iron strip attached to it. A four way switch operated by a pawl and ratchet allowed selection of the boats heading, position 2 for starboard, position 4 for port and 1 and 3 for ahead. The receiver operated the magnet connected to the switch. We launched the boat, switched on the 6 volt motor and pointed it out to the middle of the pond. I pressed the key, a burst of wireless waves and the boat started turning to starboard. Another burst and it went ahead. A third burst and it moved to port and a fourth and it went ahead. All worked magnificently. When the boat reached the middle of the pond, someone said "Now try and make it come back." I pressed the key and it turned gently to starboard, but when the boat was pointing straight back to us I pressed the key..... nothing! I pressed the key frantically a dozen times but there was no response. The boat was now turning in tight circles in the middle of the pond. As we had half expected something might go wrong. An essential part of our equipment was a highly trained dog - "Go fetch, boy!" And off he went. The trouble with dogs is that they are so intelligent. A dog swims under the surface, with only his nose, ears and eyes showing, so to grab a floating boat he has to stretch up and paddle like mad to bring it back. In a few seconds he discovers that by dragging the boat down and flooding it he can swim back comfortably, but all the electrics are drowned and that is the end of experiments for the day. The trouble (rather obvious today) was that clean, dry degreased iron filings rust over in a couple of minutes in the humid atmosphere which exists just over a pond's surface. Rusty filings don't work a coherer! However, Nickel filings work fine for several days, before they need cleaning with acid. After several trials we got it working quite well but it was rather long-winded and I got more fun operating the spark transmitter. I had learnt Morse by now and it gave a great sense of power - the loud rasping sound and the thought that you could send messages to the Nation. I never got a reply, probably because I didn't have a receiver. I bought a copy of Short Wave World and discovered a Telsen kit for making a one valve receiver for receiving the BBC. This used "Reaction" to feed back the output to the input and so increase the signal strength and selectivity, but too much made it oscillate and, to my great joy, I found that it made a noise on Father's receiver. I could now send Morse and interfere with the Stock Exchange reports when Father returned from work. I also read that if you modulate the anode current of an oscillator, you could transmit speech. I had an earphone in the anode circuit of the receiver (not recommended today in case you hear 120 volts) and if I shouted into the earphone when the set oscillated, my Mother could hear me clearly in the other set. I could now make rude remarks to Father when he switched on. I read somewhere that you needed a licence to do that sort of thing so I joined the RSGB and got an "Artificial Licence" by saying I wanted to carry out experiments on oscillators. Nowadays, we talk of dummy loads, but the term Artificial Aerials suggests dipoles and the like are natural and grow in gardens. My late wife, Pippa, insisted that they did. A well known amateur John Curnow, G6CW, lived nearby and acted as my Radio Father, so I asked him how to get a full licence. He explained that you had to write a letter to the Headmaster (the Postmaster General) detailing experiments you wished to carry out and that were not possible with the Artificial Aerial. Only propagation and aerial design came in that category, so I chose aerial design and got my licence in 1933 - or to be honest my Father got the licence on my behalf. The Post Office would not write to me direct as I was under 21. What a charade that licence business was. The terms made it clear you were not allowed to send CQ. You were only supposed to be carrying out technical experiments, so you had to send TEST. The rest of the world knew that TEST meant a British amateur was calling CQ and from then on we chatted to each other, much as we do today. For some reason the Headmaster never found out that the whole system was widely abused and just as well it was, because so many operators were already Morse friendly when WW2 broke out. If I hear Test today I switch off immediately.
Harry Heap G5HF
Newspaper reports WW2 activities of Radio Amateur G5HF The Chelmsford Amateur Radio Society run training courses for the Foundation, Intermediate and Advanced amateur radio exams.
To find out more speak to Clive G1EUC on Chelmsford Amateur Radio Society (CARS)
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