This unusual phone was designed by Mr C Langdon-Davies of London in the mid 1880s. He drew on earlier work by Francois van Rysselberghe (1846-1893), who devised the principles used by the Phonopore. Van Rysselberghe was a Professor of Physics at the Industrial School of the Ostend School of Navigation. He was still in his teens during his early career, and established a reputation for brilliance. He designed a remote-reading weather station while attached to the Belgian Royal Observatory, and it was probably this that led him into the idea of superimposing a telephone signal across a telegraph line. He may have followed on original work done by David Hughes in Britain, published in 1879. Hughes proposed the use of a choke coil to reduce interference between telegraph circuits. Van Rysselberghe patented his system in 1882, and provided details of a number of circuits to handle different configurations of lines, both single-wire and full metallic (two wire). The system caught on rapidly in Europe, where most long-distance telephone lines used his system during the 1880s.
Van Rysselberghe set out to provide a long-distance telephone using the existing telegraph networks owned by the various Post Offices. To do this, he needed to filter out the Morse signals from the voice, and the voice from the Morse. His timing was favorable. There were now many telephones in operation and the subscribers wanted to make longer-distance calls. The huge telegraph network was already in place. In Europe the telegraph networks were owned by the same State-owned Post Offices that owned the telephone trunk lines, so it was sensible that the trunk service be enlarged using the existing infrastructure. In Britain, W H Preece, the Post Office's Chief Electrician, held out on using the circuit not because of any of its own deficiencies but because the the Wheatstone high-speed telegraphy system used in Britain on the main telegraph lines may have had problems with it. In spite of this, it was eventually introduced anyway. It may have been the outcome of a visit by Preece to Paris in 1889, where he saw the system in action and was allowed to make tests on it.
The following quotation is from Poole's The Practical Telephone Handbook , 1912 edition., and it should be noted that the BPO was still using Van Rysselberghe's circuits well into the 1930s.
"By the inclusion in the battery and line circuit of high inductance coils in a telegraph line, as shown in the lower part of Fig. 516, the suddenness of the make-and-break telegraph currents can be so reduced that a telephone connected in a branch circuit of a single wire line would remain quite silent while telegraph messages were passing. As the telephonic speaking current will not affect the telegraph instruments, it was thus possible to work both telephone and telegraph on the same single-wire line, at the same time, quite independently. This system has been extensively used on the State telegraph lines in Belgium, and on a number of railway lines in other countries , and for call-wire circuits for trunk line working by the British Post Office.... By making the telephone return through a second telegraph line fitted in a similar manner (at both ends, of course) as shown in the upper part of Fig 516, it is easy to obtain an inductionless metallic circuit for the telephone. if the lines are properly balanced and twisted."
Van Rysselberghe went to the United States in 1885 to test his system over longer lines, and was able to achieve a call from New York to Chicago, a distance of about 1000 miles. Unfortunately in the United States the situation was different to Europe. Western Union Telegraph and Bell Telephones had settled their legal differences, and part of the agreement was that they would stay out each others' business. This left Bell with the need to build their own long distance network from scratch, an expensive proposition. For this reason Van Rysselberghe's demonstration, although highly successful, did not draw much further attention. Bell could not provide a direct connection between the two cities until 1892. It was not until Pupin's invention of the loading coil many years later that Bell was able to provide true long-distance calls, and by then Van Rysselberghe's work had been forgotten.
Van Rysselberghe set up business with Charles Mourlon in Brussels to make the instruments for his system. Examples of their telephones arte shown at Fred's Old Phones website at http://pagesperso-orange.fr/fredouille/musee/musee4.htm . They licensed their system throughout the world, and its success was such that in 1889 they approached the British and French governments about setting up a cross-Channel telephone line. It would be paid for by the company, and repaid by a royalty on the voice and telegraph calls made on it. The proposal was rejected by both governments, as they were becoming concerned about the amount of private ownership in the new and thriving telephone industry. Van Rysselberghe died in 1893 at the age of forty six. Although recognised and honoured in his own lifetime, his work seemed to be quickly forgotten - except in one area.
The relationship between van Rysselberghe and Langdon-Davies is unknown, but the operation of their two systems is similar. Van Rysselberghe's name lapsed into obscurity, while Langdon-Davies went on to put practical telephones into production in an area that Van Rysselberghe appears to have ignored - the railways.
Langdon-Davies sold his Phonopores through his company , the Phonopore Construction Co. Ltd., from a factory in Southall in Britain. While Van Rysselberghe had designed a system to operate between telephone exchanges or on phone-to-phone circuits, the Phonopore was designed specifically to operate across the slow speed Morse telegraph lines owned by the railways, and to meet their needs. To do this, it needed a filter to cut out the low-frequency Morse pulses from the phone conversation, and to cut out the frequencies of the voice call from the Morse, work that had already been done by Van Rysselberghe. It also needed to signal a voice call without interfering with the Morse. This ruled out magneto bells, as their pulses were in the same range as the Morse. To overcome this, Langdon-Davies needed a ringing frequency that was up in the voice ranges, not down around the Morse frequencies. Oscillators were unknown then, so he devised a "vibrator", a mechanical device that generated a ringing frequency by opening and closing very fast. It worked at about 135 Hertz. This could use a very efficient telephone receiver as a sort of bell substitute. Such a receiver was available from the Collier-Marr company. This was a bulky device and was not selling very well on their telephones, but it made an ideal loudspeaker for the Phonopore. Its output was a harsh sawtooth waveform, and the sound from the receiver was supposed to sound like the squawking of a crow when driven by the vibrator.
The distinctive Collier-Marr receiver owed its high output to the double diaphragm and massive coil assembly. An external horseshoe magnet is used to polarize the iron core of the coil. A diaphragm is set at each end of the iron core, between the core and the magnet's pole pieces. Although very efficient, its size made it clumsy for use as a handheld receiver. It was originally fitted with an earpiece, but Phonopore used a metal trumpet to further amplify the sound. Most of the residual crosstalk between the telephone and telegraph traffic was filtered out by placing a second receiver in parallel with the first. These two features gave the Phonopore telephones their distinctive appearance.
The Phonopore proved efficient and reliable in use, was almost free of induction noise and seemed immune to lightning strikes, in spite of being based on a single-wire earth return system. Much of this was due to the careful design of the filter coils fitted to each Phonopore and telegraph instrument. The Compensating Coil filtered Phonopore signals from the Morse instruments, and the Carrier Coil acted as a condenser and filtered the Morse signals from Phonopore conversations. The company proudly advertised "whereas condensers are continually failing through lightning, no Carrier has ever been known to fail from this cause". The coils were shunted to earth through efficient carbon lightning arrestors and must have worked very well. The New Phonopore Company (the company was refinanced and reorganized probably in the late 1890s to raise capital for expansion) advertised that their phones could work across telegraph lines of up to 400 miles.
Langdon-Davies sourced the transmitter, receiver, and many of the other parts from Kellogg in the United States. His company resold Kellogg parts in Britain for some years. Some early Phonopores were fitted with Phonopore-branded Kellogg transmitters. There is an example held in the Powerhouse Museum in Sydney. Many surviving instruments have WE receivers, but these were probably maintenance replacements.
The Phonopore quickly attracted attention among the Railways, and sold well in Britain and overseas. It was reviewed in the U.S. magazine "Manufacturer and Builder" in September 1885, the earliest known record so far. An early British mention is in the "Pall Mall Gazette" of May 27, 1886, where the author was intrigued by the idea of two separate signals being sent along a single wire. The company was also listed on the London Stock Exchange by 1885.
As the phones went into wider use, Langdon-Davies found it necessary to add two-line Phonopores, switchboards, linesmens' sets and intercoms to the range. A desk Phonopore was also available. He even added some standard CB and magneto telephones to the company's range, and eventually marketed a 50-line step-by-step PAX for the railways' administrative offices.
Mr Arthur Nicholson, the Chief Engineer of the New Phonopore Company, devised a party line signaling system in 1914 that allowed up to twelve connections. He did this by using relays sensitive to particular levels of current. This did away with the need to use code rings or other signaling arrangements, and greatly extended the use of the Phonopore circuit. It required a two-wire circuit, but by this time these were coming into wider use anyway. By adding a pole-changer (a device that switched the current from + to - rapidly) magneto telephones could also be used under some circumstances.
There were few other changes to the technology. The vibrators eventually drifted out of adjustment and the Collier-Marr receivers stopped working. The company designed the Resaphone, which was simply a controlled feedback device. A signal was applied to a Kellogg-based receiver module, and an attached pickup unit generated a feedback howl that was fed down the line to the Collier-Marr units. It was simple and rugged and needed no further adjustment. It probably sounded better, too, than the squawk of the earlier models. In spite of this, Mr A Harrison designed a simple screw adjustment mechanism for the old vibrators as late as 1919 to allow them to be quickly brought back into adjustment by unskilled staff. A self-adjusting unit was also produced.
Some of the telegraph noise could still feed into the Phonopore receiver when the telephone and telegraph were operating simultaneously on long lines with strong signals. Electrical engineer Mr Mark Jacobs devised a number of ways of filtering out this crosstalk by inserting a condenser or a redesigned Compensator Coil into the circuit. He patented this in 1905. Mr Jacobs and Thorrowgood, another engineer, received a patent in 1907 for a similar idea. By careful winding of a Compensating coil into a receiver, a small capacitance could be built in that further cut the noise. In practice few receivers were wound with the receiver coils, it being simpler and cheaper to add the appropriate Compensator coil into the circuit at some convenient point as per Jacobs' earlier design. The Phonopore receiver winding is noted in the catalogue as only being available in the Type RE, and it is also noted that this winding is "somewhat delicate". The later Sterling Type A did away with the extra winding and is noted in the catalogue as being "less liable to breakdown".
The simplicity and reliability of the Phonopore system must have appealed to the railways, who had few technical repair people available to them. Another attraction must have been the Phonopore's simplicity of operation - push a button, wait for an answer, and speak. A Morse telegraph required a trained and well-paid operator at each end, but a Phonopore could be operated by anyone. Because the lower frequencies were cut out by the filters, there were comments that the Phonopore sounded a bit tinny, but that appeared to be its only fault until the railways began to run telephone wires on the same poles. The Resaphone units generated rich harmonics that induced into the parallel phone lines. Since the telephone was steadily replacing the Phonopore anyway, this was rarely a problem.
The New Phonopore Company was not without competitors. Phonopore-type phones are also known from Ericssons, British Insulated and Helsby, Medhurst, Siemens and the Australian Post Office.
The British Ericsson unit was more compact than the Phonopore, and used an Ericsson receiver as the signaling unit. It was their Model N1195. The use of a handset cut down the size of the case required. They also produced a lineman's bagset. The Model N1195 appears to have been used in Australia as its circuit is shown in the 1914 Australian Post Office "Telephone Circuits" Handbook.
The Australian Post Office phonopore, their Tele 41, has been thoroughly described in the Newsletter of the Australasian Telephone Collectors Society, January 1994 edition. It was a composite of parts assembled by the Post Office Workshops in Melbourne. It also used an Ericsson receiver for the howler.
British Insulated and Helsby, a telephone and cable producer, briefly made their Pantophone. It was a compact unit that also used an Ericsson receiver.
The Siemens & Halske phone was their Model 4126, but its details are virtually unknown.
A Medhurst telephone is listed in the 1914 Australian Post Office "Telephone Circuits" Handbook, and its circuit is shown, but nothing else is known.
Around 1914 Mr Langdon-Davies sold the Phonopore business to Sterling Telephone & Electric. They continued production with the phones virtually unchanged. Production ceased in the early 1920s in the face of competition from the growing public telephone networks. Many railways liked their Phonopores, however, and the phones were often reconditioned in the railways workshops. In New South Wales Phonopores were largely replaced by telephones in the 1930s, but the last two were only finally taken out of service in 1962.
Dargan, James "Morse to Micro" 1988
For the information on Van Rysselberghe I have drawn extensively on the detailed article "Francois van Rysselberghe: Pioneer of Long-Distance Telephony" by D. Gordon Tucker, published in Technology and Culture, Vol 19, No. 4 (Oct 1978). Professor Tucker's article gives a well deserved insight into this brilliant but largely forgotten man.