AM RX using a 555 Timer IC

Nick 2E1LOK posted a pointer to this interesting blog entry on the GQRP list, and I thought that others would enjoy seeing it:

http://tubetime.us/?p=85

Stewart/G3YSX

Hans Summers QRSS TX kit

Those club member who have built the Hans Summers QRSS TX kit may be interested in an article by Kevin ZL1UJG on modifying the kit for 12V PA operation.

This can be found at http://www.knightsqrss.blogspot.com/

Stewart/G3YSX

GB3VHF - Our Local 2M Beacon

Crawley Amateur Radio Club wishes to thank the Sutton and Cheam Radio Society for permission to re-publish this article from their February 2011 newsletter.



Our speaker at the January meeting (of the Sutton and Cheam Radio Society - ed) was Chris Whitmarsh - GØFDZ. Chris is beacon keeper for our local 2m beacon, GB3VHF which is located at Fairseat in Kent. GB3VHF is just one of many hundreds of beacons located around the world, operating from HF right though to the microwave bands. The purpose of this network is for checking propagation, for the optimisation and testing of equipment & antennas and for various scientific experiments.

Most amateur radio beacons operate within the amateur bands although others operate at 5Mhz, 40Mhz and 60Mhz and require special licences. Each beacon is the responsibility of its own licensed beacon keeper who needs a variation on his or her amateur licence in order to operate the beacon. A fairly long a tedious approvals procedure is necessary to establish a beacon and this requires the involvement of Ofcom, various government organisations and the military. In the case of shared bands, such as 70cm, the procedure can be very lengthy indeed.

The UK’s beacon project started in 1958, which was 'International Geophysical Year'. The first amateur beacon to be established in the UK was GB3IGY, located near Orpington. In 1960, the beacon was moved to Wrotham where it remained for many years using the current callsign GB3VHF. The most recent move was in February 2010 when the beacon was set up at Fairseat, just 4km from Wrotham.

There have been a few changes of hardware and keying methods over the years. The original 1958 beacon had morse generated by paper punch tape, which proved to be unreliable and was soon changed to electromechanical transistorised optical disc keying with further moves to microprocessor controlled keying and EPROM keying.

The current beacon was designed and built by a team of 4, namely:- G4JNT, G4DDK, G0MRF and G0FDZ. 19” Rack construction has been used with all external connections on the front of the equipment for ease of servicing. The latest incarnation of GB3VHF now sends its callsign and locator using on/off A1A keying rather than FSK as in the past. The latest version also transmits information using WSJT JT68 mode and is locked to GPS to provide exact timing for the start and finish of each period of WSJT or Morse transmission. The Morse sequence start at each odd minute and lasts for 13 seconds and the WSJT sequence starts at each even minute and lasts for 48 seconds.

An added feature of GB3VHF is that the WSJT transmission carries accurate time information and can be used for 'Time of Flight' calculations. The time for the beacon's signal to reach an amateur’s station should be predicable. If it takes longer, the signal is not taking the shortest path indicating that some interesting propagation conditions could be about.




Getting back to the relocation of the beacon to Fairseat, GB3VHF had been operating for many years at Wrotham. However, the site has ‘changed hands’ and is now operated very much on a commercial basis by Arqiva. The combination of withdrawal of funding, high rent and difficult emergency access made relocation necessary.

The site at Fairseat is owned by BT and is used for research and scientific studies. 15 months of negotiation were finally successful and the new beacon was installed at the site by professional BT engineers. Chris showed us some photographs of the repeater hardware including the two Jaybeam 3 element beam antennas mounted on BT’s mast. These are connected (via a phasing harness) to the beacon transmitter, located in a building near the foot of the mast, using 100 metres of LDF-550 coaxial cable. The antennas are set at beam headings of 288 and 348 giving good coverage of most of the UK.

Many signal reports have been received from all over the UK and much of Europe. The addition of WSJT mode has also extended the coverage to many parts of the world.

Many thanks to Chris for his detailed, informative and enjoyable talk. Further information on GB3VHF, its history and a selection of photos can be found at: www.g0afh.com/GB3VHF

John - GØBWV

SOS Radio Week

Malcolm, G3NZP, sent the following message to his sponsors:

"A big thank you to everyone who sponsored me for the RNLI Radio week, your support was much appreciated. As you can see I raised £242.

"My other silly hobby is sailing, so I must confess to a vested interest."

Derek Hughes (G7LFC), Chairman - Lifeboat Amateur Radio Society (www.lifeboat-amateur-radio.org.uk) thanked Malcolm for his help during the event and said "we look forward to welcoming you aboard SOS Radio Week 2012.

Well done Malcom, a very worthwhile cause.

Stewart/G3YSX

Coaxial Connectors

I happened across quite an interesting article on the history of RF connectors at http://www.maurymw.com/datasheets/5A-021.pdf by Mario A. Maury, Jr. Maury of Microwave Corporation written in 1990.

I include a few exerts, but I recommend the interested reader download the whole article.

Some Early History

With the beginning of World War II, and the emergency need for higher frequency applications above 300 MHz, it was determined that the UHF connector was not suitable and that new connector designs were required. A joint Army-Navy RF Cable Coordinating Committee (ANRFCCC) was established in the early 1940s to develop standards for RF cables, rigid transmission lines and connectors for radio and radar equipment. The task of this committee later was incorporated into the Armed Services Electro-Standards Agency (ASESA) when it was established in the late 1940s and eventually was reorganized into the Defense Electronics Supply Center (DESC) that continues the important work of connector standardization for the military today.
Under ANRFCCC guidance, the type N connector was born in 1942 and featured a threaded coupling nut for connection and an air coupling interface. The N derived from Paul Neill of Bell Laboratories (New York) who was on the committee and worked on the connector. This was followed by the HN connector that was a high voltage version of the type N and featured an overlapping dielectric interface. The type C connector followed next with a twist-lock coupling mechanism for quick connect and disconnect. It was named after Carl Concelman of Amphenol. Then, as smaller coaxial cables became available, the BNC connector was developed jointly by Neill and Concelman, hence the N and C and the B for baby because of its size.

Why 50Ohm Connectors

In the United States, the predominant impedance for coaxial transmission lines and connectors is 50 Ω. The theoretical impedance for minimum attenuation is 77.5 Ω and for maximum power transfer is 30 Ω; the average of these two impedances is 53.75 Ω or rounded off to 50 Ω (see Figure 2 at right). Therefore, 50 Ω is a compromise between minimum attenuation and maximum power transfer in a coaxial transmission line, and that is why it was selected. There are connectors available with other impedances, the next most popular impedance being 75 Ω (approximate minimum attenuation performance) that is in fairly wide use internationally and in long line communication systems.



In the early days because of the lack of knowledge and the unavailability of accurate RF measuring equipment, military specifications for connectors were based on detail mechanical piece part drawings, which were non-optimum designs from a microwave standpoint, with no performance specifications. This limited manufacturers from making improvements or risk noncompliance.

The SMA Connector

The SMA connector is the most widely used micro- wave connector in the world today. It originally was designed at Bendix Research Laboratories by James Cheal in 1958 and began life as BRM connector for Bendix real miniature connector. Its development was continued in 1962 by Omni Spectra (now a division of M/A-Com) when the connector became known as OSM for Omni Spectra miniature. It became popular under that name. In 1968, it was incorporated into MIL-C-39012 where it received its current designation of SMA for subminiature A. A more detailed description on the early evolution of the SMA connector is described in a previously published work (see paper - ed).

The SMA connector was designed to be a low cost miniaturized system connector. It is a coplanar pin socket connector with a dielectric interface. It is an excellent adaptation for use with 0.141 diameter semi-rigid cable in its simplest form. It found ready application for use with stripline and microstrip circuits because of its size. People have complained about their longevity in a measurement environ- ment, but it was not intended for this application. The APC3.5 connector is a well suited test connector for SMA and is being used for this purpose on a regular basis6. The principle of interface error correction using software and a VNA was advanced6 and later implemented.

SMA connectors will operate mode-free to 18 GHz and certain versions to 25 GHz (higher order modes can exist in the 22 to 24 GHz frequency range). There is also an improved version available from Amphenol and M/A-Com that operates to 27 GHz.

An interesting statistic is, "What are the most used coaxial connector types?" In 1985 based on shipments, the top seven coaxial connectors were SMA, BNC, N, UHF, TNC, SMC and SMB. (it would be interesting to see statistics for 2010 - ed)

BEHIND THE SCENES AT BLETCHLEY PARK DURING WW2

By Dr Brian Oakley

On 24th November CARC members were delighted to welcome Dr Brian Oakley, accompanied by his wife Marion, to give a talk “Behind the Scenes at Bletchley Park during WW2”. As a wartime wireless operator Dr Oakley is well qualified in this field, and is a Bletchley Park Trustee, historian and tour guide. He is also a former President of the British Computer Society.



Aware from his military service in South Africa of the importance of secure communications, Winston Churchill as First Lord of the Admiralty created in 1914 the Cryptographic and Intelligence unit within the Admiralty, which became known as Room 40. Between the wars this went on to become the Government Code and Cipher School, which at the outbreak of WW2 moved to Bletchley Park in Buckinghamshire. Here a young generation of mathematicians and scientists was recruited and they together with the veterans of Room 40 set out to break the German Enigma codes. It was here that one brilliant man, Alan Turing, saw the need for and designed a machine to help and to speed up the decoding process. Churchill continued throughout the war to provide strong support to the BP team providing both staff and finance to meet their urgent requirements.

During WW2 8,900 people were based at Bletchley Park, many of them working to decode messages that the German forces transmitted, most notably by Hitler to the German high command. The high-level intelligence produced at BP, codenamed Ultra, was crucial to the Allied war effort. The cracking of the German codes and the use of the intelligence gained, together with the subsequent related actions of the Allies was a vital part of the Allied war effort and is said to have shortened World War II by as much as two years, with the related saving of many million lives. The critical importance of Bletchley Park in world history is therefore undeniable.

Bletchley Park is also the birthplace of the world's first programmable, digital, electronic computer - Colossus. Colossus as an idea came from the operational needs of Bletchley Park during World War II to speed the reading of Enigma-encrypted German messages. Colossus Mk 1 was designed and built by a team led by engineer Tommy Flowers at the Post Office Research Station at Dollis Hill North London and went into service at BP in early 1944. by the end of the war there were ten Colossus machines in operation at Bletchley Park.

The Enigma cipher was the backbone of German military intelligence communications. The Enigma machine dated back to 1919, when Hugo Alexander Koch, a Dutchman, patented an invention that he called a secret writing machine. It was originally designed to provide secure banking communications, but the banks showed little interest. However, in 1926 the German military, initially the Navy, saw its potential and adopted it in quite large numbers, thinking it unbreakable.

However, they had not reckoned on the ingenuity of the Poles, who by 1932 had broken Enigma, when the encoding machine was undergoing trials with the German Army, and managed to reconstruct a machine. At that time, the cipher altered only once every few months. With the advent of war, it changed to at least once a day, thereby preventing Polish intercepts. By mid-1939, the Poles had passed on their knowledge to the British and the French, thus enabling the British code breakers based at Bletchley Park to work out the order in which the keys were attached to the electrical circuits, a task that had been impossible without an Enigma machine in front of them.




Fig 2. Bletchley Park mansion today

The early attempts to break the Enigma settings and coding used an equipment called the Bombe, the initial design of which was produced in 1939 at Bletchley Park by Alan Turing. The bombe was an electro-mechanical device that simulated the Enigma by trying all possible scrambler settings,its function being to discover the daily settings of the Enigma machines on the various German military nets: in particular, the set of rotors in use and their positions in the machine and the settings of the alphabet rings.

The code breakers, armed with this knowledge, were then able to exploit a loophole in Enigma's armour. One particular design flaw meant that no letter could ever be encrypted as itself: the letter A in the original message, for example, could never appear as an A in the code. This gave the code breakers a toehold. Errors in messages sent by stressed, lazy or tired German operators also provided clues. In January 1940 came the first break into Enigma.

These messages, in the form of radio signals, were initially intercepted by the network of monitoring stations (Y-Stations), which were British signals intelligence collection sites, originally established towards the end of WW1 and revived during World War II, and the traffic was then sent onwards either by motor cycle despatch rider or land line (teleprinter) to BP for de-coding and analysis. The Y-Stations were operated by a number of agencies, including the Armed services and also the Foreign Office (MI5 and MI6). Typically more than three thousand coded messages arrived at BP each day from the 'Y' Stations. Incoming messages were then routed to specific 'Huts' for decoding, depending on whether the messages had come from the German army, navy or air force, or another source. Despite the large and imposing BP manor house building, these wooden huts - Huts 3,6,4 and 8 - were where much of the Enigma decrypt work was carried out.

The huts operated in pairs and, for security reasons, were known only by their numbers. Hut 6 contained the code breakers concentrating on the German Army and Air Force ciphers, supported by a team in the neighbouring Hut 3 who turned the deciphered messages into intelligence reports. Hut 8 decoded messages from the German Navy, with Hut 4 the associated naval intelligence hut. Their raw material coming from the 'Y' Stations: the web of wireless intercept stations scattered around Britain and in a number of countries overseas. A radio station known as Station X was also sited at BP, in the mansion’s water tower, but due to the long aerials was moved to nearby Waddon Hall in 1940.

Of those working at BP more than half were women including many WRNS. Of the men, probably the most well known were mathematicians Alan Turing and Gordon Welchman. Dilly Knox, a classics scholar, was one of the original Room 40 SIGINT cell in WW1 and moved to BP in 1940 as one of the great early code breakers.

Radio was at the heart of the work of BP, because the code breakers relied on the Y station intercepts of German encrypted radio messages on which to work. Whilst Brian’s talk concentrated on the code breaking operation, there was also a huge radio network associated with the Park that carried the resulting Intelligence material to our forces round the world - including the first point-to point microwave radio relay (The No.10 set) to Montgomery after D-day - on which Dr Oakley worked as a Royal Signaller.

Dr Oakley says of these days "As a young Army signaller in 1945 I worked with many of those who had spent the war years intercepting the enemy's communications, and sending the resulting information on to Bletchley Park, where that remarkable bunch of geniuses stripped out the encoding to read the enemy's mail, something that of course gentlemen do not do! Almost in passing they launched the computer age, building what were some of the very first digital machines".

Thus the story of places such as Beaumanor Hall in Leicestershire, Denmark Hill in North London, RAF Chicksands in Bedfordshire and some thirty other widespread stations comprising 'Y' service, the Royal Signals Regiment, and the code breakers of Bletchley Park are all inter-twined.

This was a most fascinating insight into the workings of Bletchley Park and we are indebted to Brian Oakley for setting out the importance of its massive contribution in the outcome of World War 2.


John Longhurst G3VLH

CARC Training Double

After 10 weeks of regular evening classes for five Intermediate students and a sustained period of self-study by two Foundation candidates, a joint exam day for both levels was held on Saturday 5th February. This meant that the cumulative number of questions answered between them amounted to 275, of which 261 were correct. To put it another way, their overall exam performance was 95%. How impressive is that! Now fired with enthusiasm both groups are keen to progress to the next stage and discussions about when have already begun.



As tutors, Ted and myself have received some very supportive feedback following this most recent training programme and I'm sure I speak for both of us by saying it has been a pleasure helping them towards achieving their amateur radio objectives. Last but not least, thanks to Dick Lupton for undertaking the somewhat exacting task of Examination Invigilator.

73 Malcolm (G3NZP)
Training Secretary