Sutton & Cheam Radio Society

EME (or Moonbounce), is subject that we have covered in the past, but the techniques described have usually been far too ambitious and expensive for the typical amateur to consider.

Our speaker for the February meeting was Paul Watton – G4DCV, who was able to describe what is possible on a more modest scale. Paul started his presentation by showing a variety of EME antenna installations including that of W5UN (32 x 17ele Yagis) and RB6BN (32 Long Yagis on Transmit & 64 Long Yagis on Receive). The installations looked very impressive, but not really practical for the average ‘postage stamp’ British back garden. Fine though, if you have a convenient field and very deep pockets!

Getting a signal from one earth station to another, via the moon, is a quite an achievement. At 144Mhz, the path loss is 252dB, the moon is 250,000 miles away, there is a 2.5 second delay on the return signal, the moon subtends an angle of only 0.5 deg, polarisation is a ‘hit & miss’ affair, the moon absorbs 97% of the signal, and it moves!

Paul’s first experiments with EME were back in the 1980s. The station consisted of a Yaesu FT221R with BF981 Mutek Mod and a Linear Amp with 2x 4CX250Bs and 2x 14ele Yagis or a single 19ele Yagi. Contacts were CW and the technique was to answer CQ calls.

For various reasons, there was quite along gap in Paul’s EME activities until he gave it a further try in 2004. WSJT Low Signal Software was now available and this made pulling very weak signals out of the noise much easier. Typically, a CW signal on the return leg of the EME path can be 10db below the noise floor.

Once again, Paul was using a very modest station. Yaesu FT221R, 100W Microwave Modules Linear and a single 9ele Yagi. The first contact was Franco I2FAK. It was a difficult contact, but the QSO was completed with much patience at each end. Further contacts were made with RN6BN and W5UN. Total number of EME contacts in 2004 was just 3. More power required!!

The need for a few more watts led to the building of a new Linear Amplifier. Paul’s the purchase of a couple of ridiculously cheap Russian GI-7B Triodes were used in the construction of this 700W Amp (no more than 400W at the antenna though). This made life a lot easier as it was now possible to make random CQ calls and be heard.

As mentioned earlier, most EME antenna arrays are massive. One evening, in a moment of madness (or supreme clarity), Paul replaced his usual antenna with a small 3ele (6dBd) ‘Fox Hunting’ antenna (made from metal tape measures). It was pointed in the general direction of the moon and he heard W5UN calling CQ. Paul answered and the QSO was completed although he practically cooked the antenna’s balun in the process! This could be a record for the smallest antenna used in an EME contact.

Paul is now using a 2x 19ele array and is making many regular EME contacts. As he lives in an area with a lot surrounding houses and most of his contacts are made when the moon is high in the sky. This reduces the background noise quite significantly.

By demonstrating that EME contacts are achievable with a fairly modest station, Paul may have tempted one or two people to ‘have a go’. We would like to thank him for his excellent presentation, which was well received by all present.

Our guest speaker, Nick Read – G7DND/M5DND provided us with excellent live demo of meteor detection. The timing of this meeting was particularly critical as it occurred within the Leonids meteor shower. This is a predictable event as the Earth passes though the tail of the Temple Swift comet every year. Under clear and moonless conditions, the shower can be observed with the naked eye, although a full moon would have made observation quite difficult on this occasion.

Nick was able to demonstrate a method of detecting the reflected signals originating from a couple of very convenient East European 50MHz TV transmitters. The receiving antenna was a simple 6m Delta Loop, strung up just outside our clubroom. The reflected signal could be detected audibly in the 6m band as a series of tones lasting from a fraction of a second to several seconds. In addition to just hearing the tones, Nick was running some software on his computer that was providing a visual representation of this event.

As each meteor burns up in the earth’s atmosphere, it leaves an ionised trail behind it. There is also an ionised area around the meteor itself. The graphical image Nick had displayed showed each meteor as a straight line and if Doppler shift has been detected, the line started as a curve before straightening out. This particular software can also keep a log of the strikes, so the station can be left unattended for many hours if necessary.

The second demo of the evening was meteor scatter. Nick had set skeds with two stations, one in the south west of England and the other in Poland. The plan was that both stations were to put out a series of calls for Nick between 2100 and 2115 gmt. One station was to call in the first half of each minute and the other was to call on the second half of each minute.

Detection of the signals was made possible by using WSJT4 software by K1JT. (WS = ‘Weak Signal’). The designated time came and we all watched the screen for signs of recognisable call signs. Several minutes passed, but then we saw G4PCI (the west-country station) along with Nick’s call M5DND. Unfortunately no luck with the Polish station.

Finally, it’s worth noting that most meteors range in size from a grain of sand to a small pebble. The vast majority of those that enter the earth’s atmosphere, burn up long before reaching the ground!

Many thanks to Nick for coming along to Sutton & Cheam. It was a very enjoyable evening. Nick doesn’t drive, so we’d also like to thank Steve – G1LJR for providing the transport.

Our guest speaker at the April meeting was Brin Thomas from the Amberley Working Museum, near Arundel in West Sussex. Many of the staff at the museum are volunteers and Brin is the current driver & maintenance man of a certain 1920s Leyland Bus that some of our members will be familiar with. Back in 1985, a group of Sutton & Cheam members caught the bus at Horsham Station at travelled to the museum at a maximum speed of 15mph! These days, the bus ferries visitors around the 36 acre site and doesn’t venture onto public roads any more.

The site of the museum is a former chalk quarry. The owners of the site were Messrs. Peppers & Co. and the chalk was a major constituent of lime mortar. As the site is right next to the River Arun, it was fairly easy to ship the chalk to Southampton by barge.

The site was derelict when it was taken over and one of the first exhibits was a Radio Exhibition that was set up by Ron Ham in 1979. Over the years, many of the buildings on the site have either been removed on renovated. Development has continued over the years and the museum now includes a vast range of craft and industrial exhibits, a working narrow gauge railway with fully restored steam engines & rolling stock, a varied collection of vintage vehicles, radio & electronics exhibits, displays of domestic electrical equipment over the ages and a working radio shack.

Brin’s presentation also included details of the recovery of a bus body. One of the buses on the site dates back to 1909. Originally, the museum only had the chassis and engine(s). It is a petrol-electric affair without a conventional gear box, just a simple forward and reverse control. At the time it was built, it was thought that the drivers, who up until that time had been driving horse drawn buses, would have trouble mastering a ‘crash’ gearbox (no synchromesh) and clutch! A suitable body for the bus was eventually sourced in someone’s back garden. It was being used as a summer house. It’s recovery was a fairly involved process.

Several buildings have been erected on the site over the years, including a telephone exchange, a ‘Southdown’ bus garage and the EDF Electricity Museum. In addition to all this, the site includes a variety of shops and a restaurant.

Brin also informed us of the wide range of special events that take place throughout the ‘open’ season that runs from mid March until the end of October. A full list of these, along with full details of the museum can be found at amberleymuseum.co.uk

It’s 20 years since we last visited the museum and there have been quite a few changes to the site over this period. It has been proposed that we make a return visit. Several of our members expressed an interest in this at the meeting and I’ll probably ask for a ‘show of hands’ at our AGM. If the numbers look favourable, we should be able to organise a club visit. Travelling time by car from the Sutton & Cheam area should be less than 1½ hrs.

I’m sure that all those present would like to thank Brin for his lively and entertaining presentation.

John – GØBWV