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

Some Si570 Circuits

The Si570 is a combined silicon oscillator, that has come to fame in amateur radio circles through its adoption in the SoftRock series of SDRs (or should it really be SDxs)


Silicon oscillators have the property that they are stable, but cannot be manufactures to a precise frequency in the way that quartz can. The Si570 however has an integral frequency synthesizer and so in a tiny package provides oscillator with a computer controlled output frequency.

G4EOP has several interesting pages on the Si570 including some PIC code.
http://g4oep.110mb.com/channels/channels.htm

Crawley Microwave Table - Sunday, September 12, 2010

The Crawley Amateur Radio Club hosted another very successful and enjoyable Microwave Table on September 12th, when yet again we were favoured with good weather and a good attendance which encouraged participants as in previous years to spill out during the informal sessions into the open air on to the forest area immediately surrounding the Clubhouse for ‘eyeball’ chats or outside demonstrations etc.

This event is one of several organised each year at different venues in conjunction with the UK uWave Group and we again had visitors from a wide area of the South and South-east, Oxfordshire and East Anglia with a total attendance of around 45 including CARC members which meant that we had pretty well a full house for the formal technical presentations in the afternoon session.

The general format was similar to that of previous years with an informal session in the morning with tables laid out for the ‘bring and buy’ sale in parallel with an exhibition of home constructed equipment being entered into the competition for the annual G3VVB trophy.

For those not familiar with the history of the trophy, it is awarded annually in memory of Cyril, G3VVB by the judges who in their opinion, entered the best made piece of home construction in the contest. The actual trophy is a beautifully engineered microwave power amplifier cavity in manufactured in highly polished brass intended to accept a ceramic 2C39 valve representative of the many that Cyril used to make each year for the amateur fraternity which enabled many would-be “microwavers” to get on air on 23cm or in the case of your scribe, on 13cm with the moderately high power level for those days of 35W SSB before the days of an affordable solid state PA!



After the lunch break, the results of the constructional contest are usually announced followed by the presentation of the trophy to the winner and then the main technical session with several technical talks until the close at around 16-30pm.




This year the doors opened at 10-00am as usual and by the nominal start time of 10-30am, the tables were almost full of a wide variety of items being offered for sale and the Coffee bar was in full swing with cups tea and bacon butties etc. disappearing at a rate of knots to satisfy the pangs of hunger of the early starters. As usual our two stalwarts Ted Macdonald G4TTY and Dick Lupton M0RXZ manning the coffee were kept pretty busy

Meantime, the informal chat session was well under way with old friends meeting up again and bargains on offer being picked over, - this being a good place to pick up microwave bits not readily available through main dealers.

Around a dozen exhibits were entered into the constructional display with again some excellent examples of home brew in the microwave field on display for the Judges including the trophy itself. Covering a wide range of complexity, the items being judged ranged from a nicely made Mini VNA network analyser through to a magnificent 500W 23cm MOSFET linear amplifier for masthead mounting with a remote a control unit and calibrated power meter.

During the lunch break Ted and Dick were again kept busy in serving their famous burgers and bacon rolls etc. after which the result of the G3VVB constructional contest was announced by the chairman of the judges Allan Wyatt, G8LSD and the trophy presented to the overall winner of the competition, John G3XDY for his 23cm amplifier.

There were three technical papers presented in the afternoon session. The first of these was entitled “What To Do With a Big Dish” by Mike Willis who works at the Rutherford-Appleton Research Laboratory and who described how he made the most of an unusual opportunity recently in having access to one of RAL’s large steerable microwave dishes to use on the amateur microwave bands for a weekend and some the results of the troposcatter and EME signal paths he explored .

The second paper was given by Sam Jewell, G4DDK describing the latest modifications to fine tune the design of his ultra-low noise 23cm preamplifier design which uses a MGF4919G HEMT device in the input stage to achieve a remarkably low repeatable noise figure of around 0.25 dB with an associated overall gain figure around 36dB.

The mounting of the input HEMT device is unusual in that rather than the source leads being soldered directly to the PCB earth plane in order to obtain minimum inductance, the leads are raised up above the PCB with small inductances connected to ground to provide some series negative feedback which optimise the noise figure. There are also small inductances in the gate input circuit to improve the input match and in the drain lead to optimise the output match. The profile of the HEMT looks rather like a small praying mantis insect sitting on the PCB!

Sam reported some impressive repeatability statistics for noise figure varying from a minimum of 0.2dB to a maximum of 0.3dB over a sample size of 25 units. Sample measurements have been verified with NF measurements taken at various EME conferences.
More information is available on Sam’s website at www.g4ddk.com

The final paper was delivered by Brian Colemore, G3NNS who described some of the more recent weak signal modes such as WSJT and JT65 etc. now available for use via a PC and sound card for the enhancement of weak signals. These modes employ DSP techniques and waterfall displays for Troposcatter or EME or JT6M for Meteor Scatter which will reliably decode data signals many decibels below the noise floor and use multi-tone encoding with FEC or forward error correction. These methods allow decoding even when the signal is so weak that it cannot be distinguished by ear alone.

Earlier weak signal modes developed for VLF using very slow morse (QRSS) do not cope with the slowly changing propagation effects experienced such as with EME or with burst-mode propagation as with meteor scatter.

The Round Table formally closed at around 17-00 and judging by the closing comments made by the departing participants, was felt to be an enjoyable and successful event.

One piece of post-meeting feedback was that unfortunately there had been major accident eastbound on the M23/M25 causing long tailbacks and several hours delay for our guests starting from almost immediately after their exit from the Club.

Fortunately for your scribe, realising that the A23 was already blocked northbound from Cheals roundabout, my driver managed to turn immediately right at the Football Stadium roundabout and went up through the town thus avoiding all the local blockage!


Note: the date for the 2011 Roundtable has already been provisionally set for Sunday 11th Sept 2011- Put it in your Diary.

73, de G3GRO

CARC PROGRAMME SECRETARY

I feel privileged to have been the CARC Programme Secretary for the past eight years, however I feel that with the start of the new year and a forthcoming AGM that it is time for a fresh pair of eyes and ears, and a fresh brain to take over.

Anyone who is interested should be prepared to keep a close eye on what speakers are doing the rounds locally (Radcom and other club’s newsletters are good sources), in order to contact them by email or phone. To increase the chances of netting a new speaker you need to be planning ahead by several months so as to give room for manoeuvre on both sides. I have had success with speakers in the Sussex, Surrey, Kent, Hants and London areas, and occasionally further afield. And not forgetting that we have some excellent home-grown speakers from within the club, so there is a need to know who is doing what among our esteemed membership.

Another objective is trying to achieve a balanced programme of events, so a timetable of technical based and operating or Dxpedition type talks seems a good mix. I have always tried - not always with success - to have the event timetable running 3-5 months in advance.

Each month the RSGB needs to be notified of future speakers or events so that it can be published in Radcom and given out over the air in their weekly news broadcasts. This helps us to attract visitors, and very important, potentially new members for CARC.

A prompt email or letter of thanks to a speaker after a meeting is an important final courtesy, and furthermore helps your case if you need them to come back in a year or so’s time.

The above may sound quite demanding but in fact it is not difficult or too arduous and it is fun to do. You will also have the satisfaction of knowing that you have contributed in a major way to the successful operation of our great club and the satisfaction of your fellow members.

So, if you are interested in taking over as CARC Programme Secretary please put your name forward for nomination, ideally before the forthcoming Annual General Meeting on 26^th January. If you are potentially interested but need more information please don’t hesitate to give me a call on 01342 714402 or email me at .

John Longhurst G3VLH

Programme Secretary 2002-2010

Crawley Amateur Radio Club

News of Others

Hon. President, Derek G3GRO reports exchange of greetings over the festive season with long-term CARC DX members Ron, VK6RV in Perth WA; Peter,VA3PJ in Ottawa; Ray, G3LNM near Norwich; and Ken, G3JKF in Seaford who all send their best wishes to the Club.

Ray and Ken both said that they look forward to reading the CARC on-line Newsletter and keeping track of what we had been up to.

Ken reported that he has like several of us more locally, been experimenting with WSPR and has been getting kitted up to carry out some serious comparison of an OCF wire antenna (160m to 10m) and small loops. (sounds familiar!)

Peter in Ottawa has never managed to get up his antenna tower since he moved QTH but has acquired a TS2000 and is QRV on VHF and has a built a transverter for the 900Mhz band available in Canada and the US. - Peter had been very active on 432and 1296Mhz from his previous site nearer in to Stittsville.

Ron and Eileen have unfortunately both been experiencing serious health problems and Ron, like your scribe, is not very mobile these days as a result of an infection picked up after a knee replacement operation!! He reports that he now has a poor site and like many of us he had been experiencing increasing local noise levels. He had been more or less QRT but has recently acquired an Icom IC7600 transceiver and due largely to its impressive digital noise suppression capability has recently had his first QSO on 20m in 6 years.

de : Derek, G3GRO