Equipment for communications over wires, such as telephones, telegraphs, and teletypes.

Code Practice Oscillator

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Jun 162013
Code Practice Oscillator

I found this code practice oscillator on eBay, and purchased it out of curiosity. I haven’t seen one like it before. The only markings are “SER NO 1382” engraved on the hinged cover, and a paper instruction label pasted inside the cover. The type of audio connectors used indicate that it was most likely made in the 1950s. It operates on 4 D-cells, with the oscillator potted in a green resin. The potted module appears to contain a piece of perfboard, and looks like it was cast in an ice cube tray. It is marked “CTI P/N AD183”. I haven’t managed to dig out audio accessories and batteries to test it yet… so many projects! :)

Have you seen an oscillator like this one before? Do you know when and where it might have been made? Do you have something interesting that you would like to trade for it?

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Jun 112013
British Telegraph Sounder

I found this neat old telegraph sounder on eBay back in 2008. It appears to be British, and it is marked:


I do not know much about it, other than it is clearly designed to provide both audible feedback and electrical switching. In other words, it’s a deliberately noisy relay which can both repeat an incoming telegraph signal and allow an operator to copy code by ear. It has a wooden base which appears to be intended for mounting on a wall, and it’s covered by a wooden lid with a glass window.

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May 302013
TA-1042A/U Digital Nonsecure Voice Terminal (DNVT)

The TA-1042A/U is a member of the family of Digital Nonsecure Voice Terminals (DNVTs). Basically, this is a field telephone with a 4-wire digital interface to automatic telephone exchanges of the TRI-TAC family. The wireline interface can operate at either 16 or 32 kilobits per second. There is no embedded cryptographic capability, hence the term “nonsecure”.

Two TA-1042A/U field phones may be connected together with 4-wire field line (generally WF-16/U) and operated as plain field telephones, with power supplied by local batteries connected to the terminals on the right side of each phone. They may also be connected to a digital telephone exchange, and receive their power from the exchange over the 4-wire interface. They are not compatible with analog telephone lines, analog field phones, or civilian telephone exchanges. Earlier members of the DNVT family, such as the TA-954/TT, cannot be used without connection to a compatible telephone exchange (i.e., they can’t be used as simple field phones.

Chris Story K6RWJ and I have decided to take on a project to reverse-engineer the digital interface used by these telephones, and create an interface which will allow them to be used as VoIP phones. We have dubbed the project DNVT2IP.

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