IEEE

First-Hand:Philips Telephone Exchanges and Denmark before 1960

SHARE |

From GHN

(Difference between revisions)
Jump to: navigation, search
Line 65: Line 65:
 
<p>Lately standardisation also applies to conditions within the national networks, e.g. between user equipment and network. This is e.g. the case for the frequencies used by the telephone sets to set up a call. The more equipment using the same standard, the cheaper it is to produce.</p>
 
<p>Lately standardisation also applies to conditions within the national networks, e.g. between user equipment and network. This is e.g. the case for the frequencies used by the telephone sets to set up a call. The more equipment using the same standard, the cheaper it is to produce.</p>
  
<p>What does it imply to make a simple telephone call? I think it can be best explained with a quote from a book issued in 1958 on the occasion of the 40 years existence of Philips Telecommunicatie Industrie in Hilversum. Villem Vogt describes what happens when you just make a call (and remember that the whole network operates as one big exchange) in this way:
+
<p>What does it imply to make a simple telephone call? I think it can be best explained with a quote from a book issued in 1958 on the occasion of the 40 years existence of Philips Telecommunicatie Industrie in Hilversum. Villem Vogt describes what happens when you just make a call (and remember that the whole network operates as one big exchange) in this way: </p>
  
*The exchange discovers that a user wants to make a call,
+
*The exchange discovers that a user wants to make a call,  
*It must decide who this user (the caller) is.
+
*It must decide who this user (the caller) is.  
*It must see to it that other users, who want a connection to the caller, get busy tone.
+
*It must see to it that other users, who want a connection to the caller, get busy tone.  
*It must check if there is equipment in the exchange, which can serve the caller in choosing a connection and connect this equipment to the caller.
+
*It must check if there is equipment in the exchange, which can serve the caller in choosing a connection and connect this equipment to the caller.  
*It must notify the caller (with a dial tone) that it is ready to receive his wishes.
+
*It must notify the caller (with a dial tone) that it is ready to receive his wishes.  
*It must receive information from the dial or keypad of the caller, telling it who the caller wants a connection to.
+
*It must receive information from the dial or keypad of the caller, telling it who the caller wants a connection to.  
*It must find the line, corresponding to the called number, among thousands of lines.
+
*It must find the line, corresponding to the called number, among thousands of lines.  
*It must determine if the number really corresponds to a paying user and – if yes – determine if this user is already busy in a call.
+
*It must determine if the number really corresponds to a paying user and – if yes – determine if this user is already busy in a call.  
*In the latter case it must tell it to the caller with a busy tone.
+
*In the latter case it must tell it to the caller with a busy tone.  
*If the called user exists and is not busy, it must inform him that he is called by sending a ringing signal to him and – if he does not answer immediately – repeat the ringing signal.
+
*If the called user exists and is not busy, it must inform him that he is called by sending a ringing signal to him and – if he does not answer immediately – repeat the ringing signal.  
*It must inform the caller about the obtained connection by sending him a ringing tone.
+
*It must inform the caller about the obtained connection by sending him a ringing tone.  
*It must switch through the speech connection when the called party lifts the handset in answer to the ringing signal.
+
*It must switch through the speech connection when the called party lifts the handset in answer to the ringing signal.  
*It must take care that the connection is not interrupted by others than the two parties.
+
*It must take care that the connection is not interrupted by others than the two parties.  
*It must take care that when the two parties put their handsets down again they both become idle (and can be called by others or make a new call themselves) and that all equipment used during the call also become idle and can be used by others.
+
*It must take care that when the two parties put their handsets down again they both become idle (and can be called by others or make a new call themselves) and that all equipment used during the call also become idle and can be used by others.  
*It must take care that data about the call are stored for later billing of the caller.
+
*It must take care that data about the call are stored for later billing of the caller.  
 
*It must, if the called party does not lift the handset, take care that both parties and the equipment becomes idle without (in most cases) any payment.
 
*It must, if the called party does not lift the handset, take care that both parties and the equipment becomes idle without (in most cases) any payment.
  
Line 247: Line 247:
  
 
<p>The exchange itself was built as a thick metal plate with recesses for the “relays”. Each recess of about 5x1x1 cm held a telephone lamp and 3 photo conductors. It was covered with another plate and all electric wires went through this plate. The contacts were not good. A mechanical contact changes between 0 Ω and infinite many Ω, while these contacts changed between about 50 Ω and 50kΩ. More light would of course decrease the contact resistance, but the temperature would increase and neither lamps nor photo conductors could stand this. Thus, used as selector contacts the photo conductors gave a too large attenuation of the connections through the exchange.</p>
 
<p>The exchange itself was built as a thick metal plate with recesses for the “relays”. Each recess of about 5x1x1 cm held a telephone lamp and 3 photo conductors. It was covered with another plate and all electric wires went through this plate. The contacts were not good. A mechanical contact changes between 0 Ω and infinite many Ω, while these contacts changed between about 50 Ω and 50kΩ. More light would of course decrease the contact resistance, but the temperature would increase and neither lamps nor photo conductors could stand this. Thus, used as selector contacts the photo conductors gave a too large attenuation of the connections through the exchange.</p>
 +
 +
<p></p>
  
 
<p></p>
 
<p></p>

Revision as of 21:22, 10 May 2010

Contents

Preface

Since 1959 telephone exchange technique was both my work and my hobby. A number of events from this long period (and some from before it) may be of interest for others. That is why I wrote this story. It is written from my memory, with no access to notes, and is thus a subjective presentation. The persons mentioned – and others – may have a quite different perception of the events (if they remember them) and that perception is as good as mine.

July 1946: 130 km/h backwards!

Why does one choose just the work one has? For my part I wanted to become a medical doctor until I was 13 years of age. Then I changed to a wish to become an engineer and along the road it became “something with electricity”, electronics and telephone exchanges.

What caused this change? My first trip on the “lightning train”. These trains started operation on 14th May 1935 (incidentally my wife’s birthday) when the bridge over the Little Belt was opened, and while some lightning trains went from Copenhagen in the morning to the other ends of Denmark and back again before night, others went in the opposite direction. They were streamlined diesel-electric driven trains, running as a routine with the (then) formidable speed of 120 km/h and were the only trains to be ferried over the Great Belt. They had stood still during the occupation from 1940 to 1945 but were in operation again in 1946.

I had been in a holiday colony near Blokhus on the western coast of Jutland and then on a farm in Northern Jutland for a fortnight. Then I should go to Copenhagen to participate in a boy scout camp on Ermelunden north of Copenhagen. For the trip from Northern Jutland to Copenhagen my parents had succeeded in getting a ticket to the lightning train. I could get on in one end and off in the other with no change of trains in between. I remember the anxiety of my hosts whether I could find my place and get on board – according to the schedule the train stopped for only one minute!

At that time place tickets were sold for all places in the train, as they were very much in demand. I got a ticket for a chair in what was originally a small restaurant in one end of the train. Here I sat while we went quickly down through Jutland and over Funen and Sealand. At this last leg of the trip I was in the rear of the train and a railway man came along on his way to the driver’s cabin (i.e. that is what it would have been if we went in the other direction). He asked me what I would be when I grew up and I answered that I wanted to become a doctor. Well, but if I liked it I might still come with him and see the driver’s cabin. I was enthusiastic and followed him. Along the diesel engine with its generator hanging in its elastic suspension, shaking and noisy, into the cabin. The rails disappeared under us, the landscape in the dusk flew along and the speedometer showed (logically enough) minus 130 km/h From then on I wanted to become an engineer!

The boy scout camp started another important part of my life: The connection with Holland. We were asked one day if we would have a Dutch boy scout who had been in the camp with us home for a fortnight. I phoned home and got an OK from my mother. The day we were to meet our guests I first saw Jan van Dorsten, a tall, skinny boy about 9 months younger than me. We followed each other for 39 years and visited each other. I was in the Senate’s Room in the University of Leiden when he was promoted on a dissertation about an English poet and warrior, Sir Philip Sidney, and I was a witness at his second marriage in the Town Hall of The Hague, both in 1962. He suddenly died from a heart attack in the summer of 1985 from his third wife and two small girls of 2 and ½ years.

My background

My dreams about first becoming a doctor and then an engineer were supported by my parents. They had not become students but finished with a middle school exam. Both had the ability but the means of their families or the support were inadequate.

The parents of my mother came from farmer families not far from Copenhagen. They had moved to the town in the end of the 1900ies as so many others, as there was not enough work to find in the country. My grandfather had no professional schooling and worked in the gas works of Copenhagen. He worked under the gasification ovens, where the cinders fell down when the gas had been extracted. A tale says that once a man had fallen into the nearby harbour due to too much drinking. He was saved and laid in the hot room under the ovens to dry. When he woke up and saw shapes moving around on a background of glowing cinders, it was hard to convince him that he was not dead and landed deep down. That was the working place of my grandfather.

They had 10 children in all, 8 girls and 2 boys. One girl died as a small child. They wanted to live in a more open environment than in the high-rise parts of Copenhagen (although high-rise here only means 5 stories) and could buy one of the houses in a group built in an open field some 6 km from the center of Copenhagen. My mother was 6 years of age then.

The children had to start working soonest possible for the family to stay in the house. However, my grandparents had the opinion that if there was the ability to study on, it should be encouraged. So my mother went to the middle school. She would not go on after that but support the family. I think also that she did not see herself as a person with her own career, so the middle school was enough. It gave access to an office job until she got married.

The girls were mostly married to artisans and lived in apartments around in Copenhagen. It was a great flock when we all assembled for celebrating Christmas! My mother was the last surviving of them all, she died at the age of 101 years in 2007.

One of my uncles was a sensation back in 1948. He was a tool maker and was in connection with the Marshall-plan invited to USA to learn some new tricks. Imagine back then: Such a long journey and he should even go by airplane!

No wonder that my grandparents were social democrats. Without this political party it had not been possible for them to get their own house and raise the many children. On the wall they had an embroidery “Do your duty, demand your right – freedom, equality, brotherhood”. They lived according to this – with the right sequence of duties and demands!

My father’s family came from several places. A branch had even lived in Copenhagen already in the 1700ies, before the big invasion from the country. My grandfather on that side also worked for the gasworks, but laying down tubes in the streets and caring for the street lights.

My parents met each other when they were in middle school and their two schools should make a school comedy together. In the play they were married, their daughter was a school friend of my mother, their valet one of father’s. These two were also married later.

My father got a training job in the East Asiatic Company (EAC) and was later stationed in Warsaw. In EAC it was not allowed to get married before you were 35 years (!), but my parents married when he was 25. A couple of years later I was on my way and my mother went to Warsaw too. It was in the years of depression, my father was discharged and we moved back to Copenhagen when I was only two months old. They started out having a dairy shop, later he started peddling insurances and finally got a job at the offices of the insurance company.

We became as time went by five children and our parents wanted to give us the possibilities they had not had themselves. We all became students, myself as the first in the family on both sides. Without their support I doubt if I had become an engineer and got the job I liked so much.

Just one remark more about their support: When the first part of the engineering study was over they gave me a book. Father had written in it “In case you pass the examination / there is only ground for satisfaction / but if your efforts were in vain / you will come back and win again”.

Autumn 1953: Praxis

At that time the studies for mechanical and electrical engineers lasted a year longer than the studies for civil and chemical engineers. We had namely one year of practical work as apprentices in relevant firms. I had chosen electrical installations in one firm, work in the Telephone Factory Automatic and then a time at the army’s signalling service. I broke off the latter after having heard about going with a ship from EAC to the far east as an extra assistant engineer. In this way I came to India, Pakistan, Ceylon and Burma in the summer of 1954. I just made it home for school start on September 1st!

After having worked on installations in the new town hall of Frederiksberg I came to install light in the new telephone exchange in Kastrup, a suburb of Copenhagen. Before 1953 Denmark had had manual exchanges, however with a partial automation in Copenhagen. since the 1930ies. Here you choose with a dial an exchange and an operator in that exchange put you through to the wanted number. If you would call a number in Jutland you ordered the call at the National Telephone Company and after some hours they called you back and put you through. After the 2nd world war the administrations started on a full automation. They choose exchanges from L. M. Ericsson and transmission systems from Philips. The exchanges were crossbar exchanges, i.e. the contacts sat in crosses between horizontal and vertical bars. One of each was selected and the contacts at that crosspoint switched through the connection. Also the transmission systems had to be expanded considerably, as there should be a large probability that when you made a call you also came through at the first attempt.

Kastrup was one of the first fully automatic exchanges in Copenhagen. It was also built to a much too tight time plan. When we should install fluorescent lighting the exchange was already in place and it could not tolerate any dust. But we had to hammer Rawlplugs into the concrete ceiling and crawl on the racks of the exchange to do it. We had to cover the racks with canvas covers and avoid pressure on the telephone cables over the racks. They were in lead sheets and pressure would cause the wires to short-circuit. But still: It was probably this glimpse of the telephone exchange technique which gave the final push to what I choose for work.

“What is a telephone exchange?”

I think it was in the early 1980ies I was at a party at one of my sisters, who had also invited former school mates. We talked about our different jobs and one of them asked me “what is a telephone exchange?”. I was astonished over such ignorance, but on the other hand: What did I know about her specialty? I had lived by and for such exchanges for 25 years and it was quite chocking to meet somebody who did not know what it was.

But maybe we all working with telecommunications should take this as a compliment. Our technique exists but nobody takes notice of it in daily life because it works and is easy to use. In any case when it is used for normal telephony. With some new services one can come in trouble because they are not always working in the most logical way.

But what is a telephone exchange or the telephone network? I think Siemens first used the expression “the biggest machine in the world” in their advertisements. A good expression, throughout the world there are in 2009 more than 5 billion (5 times 10exp9) telephones connected to the network, most of them mobile, or more than 1 telephone set for each 2 persons. From any telephone one can via exchanges and transmission systems choose a connection to any of the other telephones (if there are no special restrictions). With a telephone on a small Danish island one can control what happens in an exchange in e.g. Japan. And when the connection is made the two parties can talk over it with such quality that you can recognise your partner and perceive his mood.

All this is only more fantastic when one realises that there are thousands of suppliers of equipment to this network, whose devices work together without big problems.

What ties all the equipment together is the international standardisation. It started before the telephone was invented with agreements about telegraphy across the borders. It went on to standards for the interfaces where country meets country and for signals across the interfaces. There is e.g. a standard for the minimal power a call shall have when crossing a border. In one country you can have powerful microphones and a corresponding large attenuation in the national network. Another country chooses “weak” microphones and little attenuation. There are arguments for either, but on the border the standard shall be complied with.

This international standardisation got a large significance for the development of the national networks. Equipment had to be developed to comply with the standards, so it was most economical to use such equipment also within each country. It could also be easily adapted to the conditions on the border.

Lately standardisation also applies to conditions within the national networks, e.g. between user equipment and network. This is e.g. the case for the frequencies used by the telephone sets to set up a call. The more equipment using the same standard, the cheaper it is to produce.

What does it imply to make a simple telephone call? I think it can be best explained with a quote from a book issued in 1958 on the occasion of the 40 years existence of Philips Telecommunicatie Industrie in Hilversum. Villem Vogt describes what happens when you just make a call (and remember that the whole network operates as one big exchange) in this way:

  • The exchange discovers that a user wants to make a call,
  • It must decide who this user (the caller) is.
  • It must see to it that other users, who want a connection to the caller, get busy tone.
  • It must check if there is equipment in the exchange, which can serve the caller in choosing a connection and connect this equipment to the caller.
  • It must notify the caller (with a dial tone) that it is ready to receive his wishes.
  • It must receive information from the dial or keypad of the caller, telling it who the caller wants a connection to.
  • It must find the line, corresponding to the called number, among thousands of lines.
  • It must determine if the number really corresponds to a paying user and – if yes – determine if this user is already busy in a call.
  • In the latter case it must tell it to the caller with a busy tone.
  • If the called user exists and is not busy, it must inform him that he is called by sending a ringing signal to him and – if he does not answer immediately – repeat the ringing signal.
  • It must inform the caller about the obtained connection by sending him a ringing tone.
  • It must switch through the speech connection when the called party lifts the handset in answer to the ringing signal.
  • It must take care that the connection is not interrupted by others than the two parties.
  • It must take care that when the two parties put their handsets down again they both become idle (and can be called by others or make a new call themselves) and that all equipment used during the call also become idle and can be used by others.
  • It must take care that data about the call are stored for later billing of the caller.
  • It must, if the called party does not lift the handset, take care that both parties and the equipment becomes idle without (in most cases) any payment.

These are the tasks, according to Villem Vogt, which a telephone exchange shall perform. In addition it shall be so simple to make a call that anybody can do it. Even if the called party is found in the other end of the world.

The telephone administrations have indeed succeeded in this. Otherwise the telephone would not be so ubiquitous and used.

Philips had only started making telephone exchanges after the 2nd world war. Villem Vogt writes that the time was accidental, but that Philips entered the area was not accidental. It was a natural extension of an area in which they were already busy: transmission systems. It was also clear that the exchanges given time would become electronic after the development of computers (with largely the same functional details as the exchanges) during the war and the invention of the transistor in 1948. But it was also clear that Philips would have to start developing their own electromechanical system, electronics would for years be both too expensive and too unreliable to compete with the well established technique. For many years the optimists foretold that “in five years all exchanges will be electronic”. It only became true in the 1970ies.

The beginning was due to the Dutch telephone network having been smashed by the Nazis as they withdrew from Holland. Should a totally new network be made (this would take years) or should what was left be repaired? In the latter case the important traffic would sooner get going. In addition the Dutch state had as a compensation taken over all German property in Holland including the Siemens factory for exchanges in The Hague, with drawings of all parts for the exchanges (only Rotterdam used Ericsson exchanges and Amsterdam (I think) ITT exchanges, otherwise it was Siemens all over Holland). That factory was sold to Philips, who got the obligation to repair the exchanges.

It was not always easy. I heard about a problem with the selectors in the Siemens exchanges. When a selector turned and came to the wanted contact a pawl stopped the selector. In many selectors the pawl from the past had survived and worked well. In others the pawl had been replaced with a new one, made according to the same drawings. They often broke causing much speculation at Philips. All specifications had been adhered to. It turned out that the important point was the direction of the rolling of the sheet metal in relation to the orientation of the pawl when it was stamped out of the sheet. That was not part of the specifications!

1954 to 1956: Crossbar exchanges

As part of the education at the technical university Ib Carlsen from Copenhagen Telephone held a series of lectures about the crossbar exchanges from L. M. Ericsson, which had been introduced since 1953. Here I met again the equipment I had crawled upon in my practice year.

It was an extension on the course by professor Rübner in telephone technique, which laid the basis for our knowledge about exchanges (mostly systems from before 1950) and transmission systems (where it curiously enough mostly was about systems from after 1950). As to exchanges Rübner told us about magneto exchanges (my grandfather in Hvidovre had for several years yet such a telephone until a set under a fully automatic exchange replaced it) and the semiautomatic system peculiar to Copenhagen (which I knew from home), about the dimensioning of exchanges (A. K. Erlang had about 1910 started calculations of how little equipment one could use without the users noticing it. Saving of resources is not a new idea!). He also told about the telephone sets where switching and transmission technique come together but which must not cost much because there are so many of them.

With Ib Carlsen we came from the rotating selectors (mostly beautiful examples of fine mechanics) to the crossbar selectors with their horizontal and vertical bars and their use of pressure contacts. In this they were like relays, but due to the big number of contacts with roughly the same function it would be too expensive to let them be controlled individually. Therefore the common bars. 100 sets of contacts could then be controlled by just 20 coils to operate them. The change to having only 10 outlets from a selector (a vertical bar) also required another dimensioning than the rotating selectors with their typically 100 outlets. There was even an L. M. Ericsson selector called the layer cake selector with 500 outlets per selector. Such selectors were in use in Stockholm from 1931 even up to the early 1990ies!

“Transistors are so expensive”

We also had in 1955 and 1956 practical training in the laboratories of the university. Some years ago we had started making drawings where the Indian ink lines had to have the thickness of just one line when they met. Now we met with real electronics.

We worked not only with amplifier technique but had also training with switching technique. Not due to its use in exchanges, that was still some years away, but due to its use in the new invention, the computer. Thus we had training with multivibrators, both monostable and bistable (flip-flops), and with other types of binary circuits, i.e. circuits with two stable states, corresponding to the 0 and 1 of the computer technique.

All training was with circuits using radio valves (or tubes). We did learn about transistors, which were invented at Bell Labs in USA and where the first devices using them came on the market around 1957. At prices only affordable for those, who absolutely wanted the latest new gadgets. At the university it was Georg Bruun who took care of the teaching in these new components, but for my part I did not learn much. Bruun soon went into details about their properties while I had not yet grasped the basics of their working. I felt the same about field theory taught by Lottrup Knudsen: The practical connection was lacking, one could not use the theories to dimension an antenna!

The first transistors appeared at the laboratory in multivibrator circuits which we could look at during the training. Yes, look – we did not work with them and were not allowed to put power to them. The explanation: “The risk is too great that they burn out and transistors are so expensive”.

50 years later pocket calculators cost a few USD (if you do not get them for free as an advertisement) and they contain each maybe 100.000 transistor functions on a chip of a few mm², having each more computing power than all computers in the world anno 1955!

Summer 1956: Study trip to Germany

In the autumn 1955 I was elected representative in the study council of the Students Society for my fellow contemporary students. I was elected for 1½ years, as we were due to finish at the university in January 1957. Ivar Ammitzbøl had been elected first, but as he became chairman of the Society another had to be found. There was also a club council arranging parties and here Poul Vintersø had been elected.

This position implied that I should arrange a study trip for my fellows in the summer of 1956. Agreements with the companies we were to visit were taken care of by professor Rübner. After some discussions and evaluation of the possibilities (including the economical) we choose to go to the Southern Germany.

We went by train from one town to the next and Rübner had prepared many fine visits. First in Munich, where we visited Siemens (telephone exchanges) and Rohde & Schwartz (measuring instruments). Then Ulm to visit Telefunken (components) and then on to Fernmelde Technisches Zentralamt (FTZ) in Darmstadt (telecommunication networks).

Siemens showed us their newest development, the EMD-selector. EMD means noble metal motor rotating. It had a practical way to avoid noise on speech connections by using a noble metal to make the contacts (as proponents of crossbar exchanges preach). A rotating selector will imply wear on its contacts and noble metals are too soft for that. In crossbar selectors the contacts are not worn out, they just move to and from each other. For those telecommunication administrations, who had bought the idea about having noble metal in the speech contacts, the EMD-selector provided a solution: The noble metal speech contacts were withdrawn while the selector turned. Only when a test contact (of other metal) had found the right outlet did the speech contacts move in to meet their fixed counterparts.

It should be noted that Telephone Factory Automatic in Copenhagen already used a similar selector in their PABXes (Private Automatic Branch Exchanges, Business Exchanges). In it the speech contact was a silver roll. It was withdrawn when the selector turned and pressed between two fixed contacts when the selector stood still.

During the visit to FTZ we visited a relay station in their radio relay system on Grosser Feldberg. We saw something quite new at that time: Travelling wave tubes. The trip to the station was by the newest bus of the FTZ, equipped with an ultra short wave radio telephone, such that we could phone home while the bus moved along! This mobile radio was of course built with radio valves and probably took up a space corresponding to most of a cars baggage room. But already then the beginnings of public mobile telephony could be found.

There was time for more than the technical visits. In Munich we visited the Deutsches Museum, which I think is still the biggest technical museum in the world. It was quite an experience to see Rübner throw himself over an arc sender. It was the Dane Valdemar Poulsen who as the first made a radio sender for music and speech. This invention is now one of the IEEE Milestones. The spark transmitter of Marconi was only good for Morse signals. Poulsen used an electric arc in a magnetic field to generate a continuous carrier wave, the prerequisite for modulating the carrier with speech. In no time Rübner, who had obviously worked with such a sender when he was young, had taken all covers off the museum piece so he could explain where the arc and all other parts of the sender were placed. Arc senders were used up to the early 1920ies when valve equipment took over.

From Munich we went on a weekend to Salzburg and spent a couple of fine days there, including a trip to St. Wolfgang am Wolfgangsee (Summer in Tyrol, although this is far from Tyrol!). In Salzburg we visited the ruin of the old castle as a terrible thunder came along. It was weird when all lights went out, one could really believe in ghosts in the long passages!

On our way to Darmstadt we stayed a couple of nights in Heidelberg and were at the castle to see the play “The Robbers” by Schiller. With the ruin of the broken down tower as a background it was an enchanting scenery. Again we had bad weather, this time only rain, but the performance was cancelled after the first scene. Well, we went to a beer hall in the town and there a photograph was made of the whole group with Rübner on one side, all with a big glass of beer in the hand, really living up to the traditions around “Der Herr Professor und seine Studenten”!

From party to pressure

In January 1957 the examinations were history and I was an electronics engineer. There was an unbroken row of parties in the end of January, in the family and at others, culminating in the “Engineers Society of Denmark” on February 2nd.

2 days later we were due to meet for military service, and that was something of a change. Meeting early morning, being marched to get the “king’s clothes”, which were distributed to us according to the eyesight of the personnel (who luckily had quite some training). Getting the new clothes on, and then off by bus to the first training camp. Of course we did not know how the sailors’ clothes were to be put on, including the collar with the three stripes commemorating Nelson’s victories (Abukir, Copenhagen, Trafalgar, even we Danes admit to the defeat at Copenhagen!). Thus when we joined the queue for our evening meal we got a lot of demeaning remarks from the other “older” guys in the camp. Well, in a few days we discovered that they had only been in the camp for a fortnight.

Two months here, two months in a sergeants’ school and then the officers’ school in order to become lieutenants (R) the second year. We were in total 80 engineers called up to the navy that year, and of these only 5 were permanently on ships, the others came to offices. I had sailed with the EAC before and found that this was the last chance to see other than an office chair. So I asked to be one of the 5 and sailed most of my second year in the navy on the Italian-built frigates on patrol in the Baltic Sea, right close to the Sovjet Union!

Spring 1958: Exchanges with time multiplex

During the spring 1958 L. M. Ericsson made a series of lectures about a new development at the Technical University. They were about exchanges according to a quite new principle: time multiplex.

The known exchanges (space multiplex) had a separate path through the exchange for each call, and all calls existed simultaneously and at the same frequencies. The new exchange had in principle just one common path (a highway) for all calls, but each call had only access to this path for a small part of the time (maybe one millionth of a second 8000 times each second). In this short time the two ends of a connection told each other what the instantaneous value of the speech signal from its terminal was. The idea was called “resonant transfer”: The two capacitors at the ends and a coil in the highway formed a resonant circuit. The ends were connected to the highway for a time corresponding to half a period of the oscillating frequency of this circuit. The voltage could then be passed on to the other terminal. From these samples all frequencies up to 4000 Hertz (cycles per second) could be reconstructed. This is also called PAM, pulse code modulation. A connection occupied the highway 8000 times a second, possibly for only one millionth of a second each time. This is 1/125 of each second, and between the instantaneous values of one call instantaneous values of other calls could use the highway. Not quite for 125 calls, the highway had to be discharged between two samples to prevent spill-over (crosstalk) from one call to the next..

It lasted to the 1980ies before the principle was developed so far (and there were components to do the job economically) that time multiplex was introduced at a large scale in the exchanges. The first was Northern Telecom’s SL1 PABX, introduced at Jutland Telephone. The next was L. M. Ericsson’s MD110 PABX, introduced at Copenhagen Telephone and Funen Telephone. They both used PCM, pulse code multiplex, where each sample was transferred as a digital code indicating the nearest of 256 amplitude levels. At this time Copenhagen Telephone also introduced Philips’ TBX PABX , which used PAM. This was at the time a much more economical way to transfer the samples and TBX was installed at several hundreds of the administration’s business customers.

Back to 1958, 22 years earlier! I had a liking for telephone exchanges since I crawled on top of the racks of the Kastrup exchange in 1953. The liking had increased during the lectures by Ib Carlsen from Copenhagen Telephone at the technical university on crossbar exchanges. My final study project treated “ring-shaped ferrite cores with a rectangular hysteresis loop and their use as switching and memory elements” and was done at the Teletechnical Research Laboratory under professor Jens Oskar Nielsen. Thus, when Gunnar Svala from L. M. Ericsson lectured on a new type of exchanges in 1958 I was interested, although I was in the navy and most of the time sailing in the Baltic Sea to supervise Sovjet activity there. Luckily we were during this period often in Copenhagen and I got time off to follow the lectures.

One day a gentleman asked me if I profited from the lectures? He had observed that I made copious notes. This was Max Hansen, head of Philips Telecommunications in Copenhagen. He was looking for an employee to take care of switching, and this led to us making an agreement about employment already in the middle of 1958, long before I was due to leave the navy on February 1st, 1959.

Our first agreement was that having done with the navy I should move to Hilversum and work in the development laboratory. I had married in March 1958 and my wife was to go with me. Philips could only promise us a rented room to live in, due to the housing shortage in Holland, which was much worse than in Denmark.

After some considerations we decided that the idea of a rented room was not attractive. Thus in a weekend when I was in Copenhagen (otherwise I sailed again in the Baltic on board “Diana”) we talked it over. We did not yet have our own apartment, I was sailing and we were going directly to Holland when that was over. My wife therefore lived in with her parents and so did I in the weekends. It was not very satisfactory to wait such a long time before we got our own place.

The result was that I wrote to Philips that after all I would not go to Holland for a prolonged time. They had to find another. And we started looking for our own apartment. This was easy if you would pay. We got our place in a new settlement in Hvidovre. It was very modern, only one store and with a small garden and it had been difficult to find tenants due to the price (corresponding to 50 USD a month and 500 USD as a downpayment, but my wages in the navy were only 150 USD a month, there has been quite some inflation since then). We were approved of even if we had no children to rent one of these houses. This spoiled my wife’s dream about buying a scooter, she paid the “entrance fee”!

Philips wrote back that they were willing to change the agreement so I were to work in Copenhagen. There would be some travel activity, especially that I would have to spend some months in the beginning in Hilversum. This was then the final arrangement.

The policy of Philips towards their employees was outstanding, in a large measure due to the CEO S. A. Windelin and the HRM Jørgen Holm. From the beginning I came under the pension arrangement, and although I might have preferred a 10% higher wage it is a large benefit now that I am retired. Jørgen Holm also said that they knew well that the navy did not follow the law of the land. I would not get money from the navy for my holiday in 1959, although I had worked as an officer almost the whole of 1958. But Philips would nevertheless give me 3 weeks paid holiday in 1959!

January 1959: Hidden agenda (1)

My first travel with Philips was half a month before I should actually start with them. But it fitted with an appointment with Copenhagen Telephone that they should see the development of an electronic exchange, ETS1, my future area.

I learned what the most important aim with the trip was when we after an interesting and thorough explanation of the exchange went to another demonstration. The chief engineer J. A. R. Nielsen from the administration was seated comfortably, while we all formed a semicircle around him. Then Philips explained and showed their new transistorised carrier frequency equipment. Remember that we were only about 10 years after the invention of the transistor, and here Philips dared use it in professional equipment that were for sale and should last for many years with a guaranteed reliability!

The demonstration must have been convincing, as must the price. In any case this led to the installation of this 24-channel equipment in the North of Sealand, from Hillerød northwards, such that Copenhagen Telephone could handle the demand for subscriptions and calls without investing in new cables.

ETS1, Electronic Telephone System 1

Let me come back to the electronic exchange. I learned in 2009 something about its earliest days, even before the visit in January 1959.

This came about in the following way: I had in 2005 or thereabout seen the name of a former colleague, a Norwegian MSEE working in Hilversum, in the IEEE Foundation “List of Donors”. With the name E. A. Aagaard he would naturally be at the head of any alphabetical list! I asked IEEE for his mail-address, which I got (after IEEE had checked with him that it was OK) and we wrote some mails to each other. After retirement some 20 years earlier he lived in Sevilla, Spain (he was already in Hilversum married to a Spaniard).

We did not work together on a daily basis, as he was the whole time busy with predevelopment. And after having read in the GHN what I wrote about my work in the development of ETS3, a later version of the exchange, in the early 1960ies, he filled me in on the very early days of these exchanges, as follows (in my translation, we wrote to each other in Norwegian and Danish):

“ETS3 was originally based on an idea (a patent) issued to Alfons Heetman, MSEE and later professor at the Technical University Eindhoven. My (i.e. Aagaard’s) first task at Philips Hilversum was to investigate and solve problems with the implementation of the idea (modelling and specification of the thyristor ATZ10 and its use in telephone exchange circuits), such that the later planned development of ETS3 would be possible without surprises during test and use. For the technical and planned development of the logical control similar electronic basic problems were investigated and solved by the MSEEs Kok (the core amplifier) and Kager (ferrite core properties). A larger group of employees got the job to use these basic techniques in the construction of an ETS-prototype (ETS1) for trial operation. The responsible head of this was Count Six, also an MSEE. This took place before the actual development of ETS3”.

Summer 1959: Electronic metering

One of the first devices developed for public telephone exchanges by Philips was a metering device. Such an equipment was set up for testing at Copenhagen Telephone in their exchange in Valby. There is a description of it by telephone engineer Borup in “Teleteknik” sometime in 1960.

There were a number of ring shaped ferrite cores (2,5 mm outer diameter) per subscriber. One was magnetised by the same current that went to the normal electromechanical counter, the next was written by the control circuit when the first had been read and found magnetised (to ensure that each metering pulse was only counted once). There was also a row of 16 cores forming a counter with 4 digits.

The control circuits used core amplifiers to make the logical decisions. They had proved their reliability in telegraph exchanges which were a large area for Philips Hilversum in these years. A core amplifier consisted of a transistor and some ring shaped ferrite cores in such an arrangement that when the magnetisation shifted during a read out (if the cores had been magnetised beforehand) the transistor conducted and ensured that the cores were thoroughly demagnetised. The result was a well defined current pulse which could magnetise other core amplifiers in the logical circuits and left this core amplifier totally demagnetised (or rather: magnetised in the other direction).

The equipment showed the strength of electronics, the high speed. This speed made it possible to have just one control for all 400 counters, where the electromechanical counters have individual controls to e.g. make the tens go one step forward when the units change from 9 to 0. The equipment worked by having the control look at one counter at a time. It read the cores and - if there was a new metering pulse – the counter was increased by 1 and it was noted that this pulse had been seen. The control could handle all 400 counters in such a short time that it could definitely detect every single pulse and every single interval between pulses. The latter was important. While it was less important if a counter was read during a pulse (the core remained magnetised until the control came along the next time), it was important that the control came along twice in each interval. The first time it would still see the magnetisation caused by the pulse and set the second core. But next time the core would be demagnetised and not give an output. Thus also the second core was left demagnetised by the control and the counter was ready for the next metering pulse.

The concentration to a single control gave another advantage: When the counters were to be read out after a month or a quarter-year it could be to a data medium which could be treated electronically all the way through. The electromechanical counters were photographed once a quarter-year and the pictures read by “punch-ladies”, who keyed the counter states into the computer. Naturally the boxes around the counters were also photographed, so on each picture there were some boxes on which a directory number could be seen to ensure that the correct subscribers were billed. With the electronic metering equipment the read-out was to a teleprinter with possibly a paper tape puncher added. A read-out started with an identification of the equipment and then followed all counter states in their proper order. A punched paper tape could be directly read into the billing computer.

One thing was neglected in the development. A teleprinter is after all a mechanical device with motors, blowers etc. It was built to last for e.g. 10.000 hours of operation, but that is in constant use only a little more than one year. The experts in electronics, who had developed the equipment, had not thought about this. However, teleprinters can be so constructed that they automatically stop if new data have not come during one minute or so. The only thing active in that case is the receiving circuit itself. As soon as new data arrives the teleprinter starts again. But it takes a couple of seconds before the motor has reached the correct speed and data can be received correctly.

Thus, we changed the equipment such that each time it should give a read-out, it sent an arbitrary character to start the teleprinter, waited for 3 seconds and then began sending the data. The teleprinter could now be adjusted to stop in the pauses between read-outs, and the 10.000 hours operation was extended over many years.

A problem remained which only appeared in Denmark. When the equipment was installed and connected to a teleprinter borrowed from the telegraph administration it all seemed to work. However, the print-out was gibberish. It turned out that there were different standards for the two states on the telegraph line in Holland and in Denmark. Where Holland used no-current, Denmark used current. This caused all characters to be changed into others, mostly quite arbitrary. It was easy to repair when the reason was found. A simple change of two wires to the contacts of the telegraph relay, which sent data out of the equipment, solved the problem.

The power supply to the equipment worked in “switched mode”, i.e. a power transistor shifted between full blocking and full conduction such that there were no losses in it (ideally). A coil gave a constant current to the control circuits. A power diode supplied current to the coil when the transistor was blocking. This type of SMPS (Switched Mode Power Supply) was used in all equipment from Philips Hilversum years before they became more common.

The head of development of telephone equipment with electronic control was M. J. Schmitz. We had a very good relation. He visited Copenhagen a couple of times in connection with the metering equipment and Max Hansen asked me to invite him out an evening with my wife. She was at that time secretary for a major industrial CEO and had the contacts, so she arranged tickets for “My Fair Lady” for the same evening (it was shortly after its opening, so all was sold out long time beforehand). We got the places on the 1st and 2nd row, which were kept open for the director of the musical (in case he came along). Schmitz also visited us at home, as I visited him in his home in Hilversum.

At that time we lived in Hvidovre and that name was impossible for Schmitz to remember. But he found a way: He remembered it as “widower” and you can not come much closer than that!

Another of his ways to remember: One person at Copenhagen Telephone, with whom we discussed, was a mr. Hulvej, a friendly elderly man with much knowledge about the Copenhagen telephone system. Schmitz remembered his name through another friendly elderly gentleman, viz. Maarten Toonder’s king Hollewijn, a well known figure in a strip then.

The metering equipment never became more than a field test. A general introduction of it would not pay off. One reason was the price at which it could be sold. Electronics was still rather expensive and the control could only serve a limited number of meters. The reliability was also a problem. It was too risky to entrust metering data for a large number of subscribers to just one control. In addition the routines about photographing meters and punching the readings were well established and not too expensive. That was what the equipment was compared with, and just as for telephony switching in general the old ways with relays and electromechanical meters were fast enough and were more reliable (unless the control was duplicated, as would be its price). Thus an analysis of price against performance would favour the old technique each time until the middle of the 1970ies, 15 years later.

UB49: Auxiliary functions with ferrite memories, relay controlled

Around this time (1959) electronic circuits were also introduced for auxiliary functions in the UB49 PABXes (business exchanges) of Philips Hilversum. They were electromechanical exchanges with 100-point rotating selectors which could search over 300 outlets per second and stop at the right point. The selector was invented by professor Unk. The electronic circuits had some magnetic cores per exchange line (line to the public network) and showed for the operator the number of the exchange line and the number of the extension (internal telephone set) to which an operator had connected the line. When a call returned to the operator (e.g. because there was no answer) she could see immediately whom the external party was waiting for. Writing and reading of the cores was controlled by relay contacts!

The selectors used by Philips had moving arms of phosphorous bronze, thus not a noble metal. But when such an arm slid over the fixed contacts any oxidation was worn off. There was in this way no noise on the speech connections.

UB49: Group calling

Philips had a UB49 exchange in service for their own offices, as the Danish administrations allowed three types of subscribers to have their own PABX. It was embassies, public authorities with their own technical specialists (e.g. the State Railways) and suppliers of PABXes, who might have a commercial reason to have an exchange of their own in operation in Denmark. Thus, Philips Copenhagen had since 1954 had their own exchange in operation. This also gave flexibility if there were special requirements from the users. Such a requirement from Philips Light was that calls to their ordering office should not go to the individual telephones, which might be busy while another telephone was idle, but to a free telephone if there was one.

The solution was of course group calling, where a call to a busy number automatically goes on in a series of numbers until a free number is found. Only if all extensions are busy will a caller (such as the operator) get a busy signal. Such group calling was not yet a part of the PABX functions.

UB49 had a marker for the whole exchange, divided in a marker for the group selectors (i.e. in which 100-group the called number was placed) and one for the final selectors (i.e. for the two last digits). The job for the marker is, when the called number is known, to steer the selectors to the right outlet. It is in use in about one second for each call and therefore one marker is sufficient for the whole exchange. Naturally it has to work with a large degree of reliability and therefore its relay coils and contacts were doubled.

I found how for Light (with all extensions in one 100-group) a relay could indicate if an extension was busy. The contacts of this relay could then shift the test voltage (which would stop the selector) to another outlet of the selector. In this way e.g. no. 741 could be marked, but if it was busy the test voltage would stop the selector at no. 743 (if that number was free, otherwise the test voltage would pass on to the next outlet). I sketched this solution and sent it off to Hilversum for confirmation. The confirmation came, but with a number of diodes put into all test paths. I found them not motivated and said so to Max Hansen. But while I stood there I realised that the diodes were very much required, otherwise the markings in the 100-group of Light would be extended to all 100-groups! And even worse: The marking voltage would go back and forth in the wires between the groups, marking several numbers. So I said “Oh!” and Max said later he had never seen it so obviously that somebody realised he had made a fault. The group was set up with diodes and worked as intended.

The Meadow Road Arrangement

Another example of the adaptation of the telephone exchange to the users was the Meadow Road Arrangement. Further out on the island of Amager than where the main offices were placed Philips had a factory on Engvej (Meadow road) for Neon tube signboards. They made individually designed signboards for each customer, and both sales, drawing office and production were under one roof. They were dissatisfied with the telephone system, because if somebody was not on his place and the telephone rang, there was no answer. They might use single transfer keys, but expected that people would forget to use them. An alternative would be to have a battery of telephone sets at the reception, one parallel with each office telephone. It would be difficult for the people in the reception to distinguish which telephone rang, and this killed the idea. Then the transfer keys could be placed in the reception and be switched over by the people there. But when somebody was not in his office it was not always because he was out of the building, he might visit the production and then the reception did not know he was away from his office.

My task was to solve this problem. I started with a talk with the people in the Neon factory to define the problem and learn their reaction to possible solutions. Then a proposal and a new discussion until we agreed on a feasible solution. Finally the drawings were made, such that the small workplace of Telecommunications could make the arrangement.

The result was a box with two lamps and a key with contacts for each extension at the Neon factory. One lamp was on during ringing to an extension and a common buzzer made the attendant notice the ringing. The other lamp was on when the extension was off hook. Thus the attendant could see if the user answered himself. The key had three positions, in the first the line was extended to the user, in the second it was extended to a common telephone set in the reception, in the third the attendant could speak with the user while the line to the PABX was held busy. If an incoming call was not answered the attendant could answer it. If the user should go off hook during this, the attendant could see it, connect to the user and put the call through.

It was not only the electrical diagrams I had to prepare. The workplace which mostly took care of minor adaptations during the introduction of carrier systems in these years also needed mechanical drawing of how to make the box. It resulted in a wooden box with a metal plate as a slanting upper side. The whole electrical system was mounted on the rear side of this plate. The plate was recessed in the sides of the wooden box and I remember I had indicated spacious tolerances around it, as the edge on which it rested was rather wide. The technician in the work place did not like this, he did not need a tolerance of ±1 mm, when he could make it with a tolerance of ±0,1 mm!

The equipment fulfilled a need and was in operation for several years until the Neon factory was disbanded. Neon signboards were not the fashion in the 1970ies. I had forgotten all about this arrangement until it appeared at my 25 year jubilee in 1984. There my “first project” was shown together with an operator desk from the TBX exchanges, which were sold in great numbers these years. More about that later.

PABX with “optical relays"

It must also have been in 1960 that J. L. de Kroes, daily head of telephone developments, visited Copenhagen and Århus to show a development project from the laboratory. There was a hectic search for electronic means to replace relays and selectors in the telephone exchanges. The problem was that the new means should compete economically with the established ones, and that was difficult. In addition it was not the same means which were the answer for all sizes of exchanges.

This development project was a small PABX for only 10 extensions. It should have both logic circuits and selectors in the same technique, and for this “optical relays” had been chosen, i.e. incandescent lamps as “relay coils” and photo conductors as “contacts”. This was not something de Kroes wanted to reveal, it was a big secret. His assistant Reichenberger set the exchange up with the assistance of Max Andreassen, our head of telephone installations, and me. We asked of course all the questions we could imagine and found out how the exchange worked. At the lunch, when the exchange was ready and de Kroes grilled me about it, Reichenberger was quite sorry that he had told us so much. However, de Kroes took it in his stride, it was not more than he had expected!

He asked me what was the most characteristic about this exchange compared with exchanges with electromechanical relays? I think that my answer “Its technique uses only make-contacts” was exactly what he himself would emphasise.

The exchange itself was built as a thick metal plate with recesses for the “relays”. Each recess of about 5x1x1 cm held a telephone lamp and 3 photo conductors. It was covered with another plate and all electric wires went through this plate. The contacts were not good. A mechanical contact changes between 0 Ω and infinite many Ω, while these contacts changed between about 50 Ω and 50kΩ. More light would of course decrease the contact resistance, but the temperature would increase and neither lamps nor photo conductors could stand this. Thus, used as selector contacts the photo conductors gave a too large attenuation of the connections through the exchange.