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.

Hill top excursions to Reigate Hill - lousy weather is usually obligatory, particularly when taking part in a contest! The 6M WAB contest was particularly notable for Sandie Looker - M3XSL as she made her first contact outside the UK (to Hungary) on this occasion. Oaks Park is also a favourite operating location, with cold & wet weather thrown in!

One major activity for the group was JOTA. This included a radio talk for the scouts, some kit building, morse tuition and an opportunity to send greetings messages on VHF & HF. A further radio ‘play day’ has also taken place at the Banstead scout hall.

The second part of Martin’s illustrated talk was a brief report on the foundation course that was run at the 7th Banstead scout HQ in April. The course consisted of 2 days training, 1 week to study the course work, a revision session on the second Saturday morning with the exam itself in the afternoon. A group of youngsters and adults (12 in total) sat the exam. The net result was 5 band new M3s! We understand that a least one of the youngsters who only just failed the exam is hoping to try again in the future. Further foundation courses have been planned.

The final part of Martin’s presentation was on the subject of Multimeters, particularly the comparison of the characteristics and operating techniques of Analogue and Digital meters. Basic advise was given on purchasing a good quality analogue meter, particularly making sure that it has high sensitivity of 20K.Ohm per Volt or greater on DC voltage ranges. Anything less would be unsuitable for electronic testing. Extreme caution should be exercised when purchasing a cheap meter although it should be possible obtain a suitable instrument for as little as £15.00.

Anyone purchasing their first multimeter may find a digital one easier to use, particularly as they have a very high internal resistance (at least 1M.Ohm & often 10M.Ohm) and take negligible power from the circuit the are testing.

With an analogue meter it is often necessary to account for the internal resistance of the meter to calculate an accurate reading.

Martin described the various common sense precautions that are recommended when using mutimeters along with an explanation of the internal circuitry and the various techniques employed for testing, diodes, zener diodes, transistors, thyristors, coils, chokes, fuses, bulbs and batteries.

It seems that Martin is an avid collector of multimeters and he bought along a variety of his treasured instruments for everyone to study at the end of the meeting. He packed a lot into the meeting and it was greatly appreciated by those members who came along. Many thanks to him for an excellent presentation.

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.

It was something of an appraisal of Yaesu equipment for the most part with the following transceivers on display:

• FT857
• FT817
• FT847
• FT897
• FT690
• FT290

FT290RI	FT897	FT817

Also present was a Kenwood R-1000 receiver, an Icom IC703 transceiver, a Diamond RHM5 multiband antenna and a SMB Electronic 2m/70cm antenna complete with a 9m long telescopic fibreglass pole.

Having reached the end of our discussion on all of the above equipment, Martin told us that he had brought along a PSU and offered to ‘fire-up’ any rig or rigs that we might be interested to see working. Strangely enough no-one seemed in the least interested in this idea - perhaps having a working radio at an amateur radio society meeting was rather too radical a thought!

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

It’s been a while since we have covered HF aerials, so it’s high time we re-visited the topic. Also, recent changes to the licensing structure have led to a whole new group of radio amateurs becoming active on the HF bands for the first time.

Roger started with a few of the basics of HF propagation, including the properties of the different layers of the ionosphere, such as frequency versus absorption and reflection for each layer. The relationship between vertical critical frequency and Maximum Usable Frequency (MUF) was explained. MUF being approximately 2.5X the critical frequency.

The longest possible ‘single & multiple hop’ propagation is achieved with the signal hitting the highest ionised layer at the shallowest possible angle. For this reason, the radiation angle of the antenna is very important, which led us neatly onto the basic types and characteristics of various antennas.

Horizontal aerials are affected by the ground, which acts as a reflector. In the typical back garden environment, this means that they radiate at a high angle with a short skip distance. Fine for working around Europe, but not well suited for DX operation. Beams are an option and to keep the radiation angle nice and low they should be located 3 - 5 wavelengths above the ground - totally impractical for the lower HF bands ! Single element verticals are a simple option, giving omni-directional low angle radiation.

A few practical aerials were explained, including horizontal centre-fed dipoles, trap-dipoles, end-loaded dipoles and end fed wires (such as the Inverted ‘L’). For practical reasons, these antennas can be ‘dog-legged’ to fit into the average suburban back garden.

As most modern transceivers are designed to work into a 50 ohm resistive load, matching is particularly important. Either the antenna can be designed for a correct match, or a suitable ATU will need be used.

It’s also possible to check the level of mis-match with an Antenna Analyzer. Various commercial devices are available from manufacturers such as MFJ and Autek. Everyone had heard of MFJ, but no one seemed to be familiar with Autek. Details of this range can be found at autekresearch.com/index.htm

Roger covered some of the basic designs of matched antennas, such as wires for single bands with ¼ wave resonant lengths and including the effect of length versus diameter on bandwidth. Harmonically related dipoles could be used. For instance, a dipole constructed for use on the 7MHz band would be a reasonable match at it’s third harmonic at 21MHz. Alternatively, a ‘Nest of Dipoles’ could be used. That is several dipoles all fed at one point.

Many modern transceivers have a build-in matching unit, but this is usually only suitable at an SWR of no greater than 3:1. An external ATU will be necessary in most cases.

Practical common sense advice was offered, such as keeping the antenna clear of earthed objects such as trees and buildings. Feeding inverted ‘L’ antennas from the far end, well clear of the house. EMC considerations were covered, such as keeping the antenna well away from house wiring, TV aerials and burglar alarm wiring etc.

On the subject of planning permission, Roger drew our attention to an RSGB booklet, which is free to members. The ‘4 year rule’ was mentioned. Basically, if your antenna has been up to 4 years and no one has complained, you shouldn’t have any problems and don’t apply for permission for what you’ve already got !

All in all it was an interesting evening of basic common sense advice and information. No complicated mathematics or theories, just a bit of encouragement to either start or carry on experimenting with elevated wire.

We finished off with a short Q&A session and then let Roger escape back to deepest Hertfordshire. I’m sure all those there present enjoyed the meeting and would like to thank Roger for coming along.