Fellow members,

It's been with interest that I've viewed the huge antenna arrays put on top of PRR locomotives and hacks for radio service in the "old" days. How did these "inductive telephones" work in contrast to our "modern" UHF and VHF radio systems?

THX all,

de Don, n2qhvRMLI

http://www.rmli.org
n2qhv@arrl.net

> How did these "inductive telephones" work in
> contrast to our "modern" UHF and
> VHF radio systems?

"Radio" involves radiation of the signal, not induction.

The system was intended to allow the engine and caboose to communicate, not to allow the train to communicate with e.g. an operator or a dispatcher.

The antenna set up an inductive signal in the communication lines (which would have been ferrous or copper "open wire") along the right of way.

JAC

>In re the old PRR trainphones: They transmitted and received on very low frequencies below the commercial broadcast band. The transmitted signals were inductively coupled into the wayside telephone and signal lines via the 'handrail antennas' on locomotives and cabooses, which acted as carriers of the signals, sort of. The system never worked well and was useless in electrified territory where all the telephone and signal lines were in shielded cables to keep out inductive interference from the 25-cycle traction power.

The 'trainphone' technology was abandoned when VHF two-way radio became available.



aeriola@adelphia.net

Gentlemen,

THANK YOU! I was wondering about that "inductance" part of the terminology! Now I get it.

The lo frequency transmissions must have had some serious power output to get into the telegraph wires and produce a useable signal equal to the length of a train, fore and aft. Do you know anything about the transmission equipment used by the PRR, it's history or manufacture? Does anyone know of any technical manuals, books or the like surrounding this historic equipment?

Thanks again,
de Don, n2qhvRMLI

http://www.rmli.org
n2qhv@arrl.net

All the Trainphone equipment was made by Union Switch & Signal. Several manuals were published, but given the limited production (aside from PRR I'm only aware of a test installation on B&LE) they would be pretty rare now. The information posted from others is basically correct. In order to pump out enough power for any kind of reception huge amplifiers were required. Even so, reception was limited to several hundred feet either side of the dedicated line wire that acted as the stationary antenna. The low frequency (typically 30-50 kHz) dictated very large antenna dimensions. All in all it was a limited success. PRR stopped installing it on new locos about 1962/63 and when dependable solid state VHF radio gear came along, all the Trainphone stuff went in the dumpsters quickly. One amusing sidelight was Bessemer's use of portable sets. It consisted of a housing about the size of a lunchbox surmounted by a huge antenna coil at least 3 feet diameter. Can you imagine switchmen or brakemen trying to carry around a thing like that today?

Dave Hamley, K3PRR

> Gentlemen,

> THANK YOU! I was wondering about that
> "inductance" part of the
> terminology! Now I get it.

> The lo frequency transmissions must have had
> some serious power output to get into the
> telegraph wires and produce a useable signal
> equal to the length of a train, fore and
> aft. Do you know anything about the
> transmission equipment used by the PRR, it's
> history or manufacture? Does anyone know of
> any technical manuals, books or the like
> surrounding this historic equipment?

> Thanks again,
> de Don, n2qhvRMLI


K3PRR@verizon.net

> Fellow members,

> It's been with interest that I've viewed the
> huge antenna arrays put on top of PRR
> locomotives and hacks for radio service in
> the "old" days. How did these
> "inductive telephones" work in
> contrast to our "modern" UHF and
> VHF radio systems?

Hello Don,

I was interested in your posting on the railway group. I have been trying to research the early days of radio, before Marconi.

In around 1890 the British Postmaster-General, William Preece, noticed that telephone conversations on an overhead line going up the east coast of Britain could be heard on a similar line going up the west coast, about 100 miles away. He developed an inductive communication system to link a lighthouse on an island in the Bristol Channel with the mainland 4 miles away.

The snag with the system was that to get that distance involved a square of wire around the entire island - not too practical in town!

It sounds like the system used on the railway system you mention made use of the overhead telegraph lines and rails as a sort of
inductive loop - William Preece would have approved!

73, Richard G3VGW

Ambergate, Derbyshire, England



richard@g3vgw.demon.co.uk

Did some round end observation cars have the antennae? Was this for the crew, or for first class passengers' telephone calls?

104577.651@compuserve.com

> Did some round end observation cars have the
> antennae? Was this for the crew, or for
> first class passengers' telephone calls?

The short answers are no, no and no. Longitudinal antennae on the roof of streamlined passenger cars were almost invariably for the radio in the lounge section of the car.

pnichol6@prodigy.net

But.....most company business cars were equipped with the inductive trainphone equipment. Car 120 was equipped with both the transmitting loop and twin receiving coils during it's 1953 shopping at Altoona. By the time we got the car the recieving coils were gone but you could see where they were mounted and the 3/4" stranded copper loop was still inside the wooden support frame. We disposed of the wooden frame, but duplicated with steel angle for appearance sake.

EBL

Elevin120@aol.com