What is it?

[TonyDuell]

Does anyone know what this unit is?

The photos show the unit with the carrying case, the internals (the empty space is for a PP3 battery which gives an idea of the size of the unit) and the component side of the PCB

I've also attached a reverse-engineered circuit diagram.

It generates a 1800Hz tone when you press the button. The frequency is determined by a Murata resonator and is therefore quite accurate.

It's clearly a commercial unit (custom moulded case, the carrying case) but there's no maker's name anywhere on it. The transistors are Japanese 2SC... types.

One suggestion is that it's a simple remote control for a telephone answering machine, but does anyone know for sure?

[Nickthedentist]

I think the answering machine interrogator is extremely likely, or some other application which relies on a tone being sent down the phone.

[G6Tanuki]

Some Continental amateur radio repeaters needed an 1800Hz toneburst in place of the then-UK-standard 1750Hz.

I wonder if this 'thing' could have been sold to allow UK hams with a 1750Hz toneburst to access Continental repeaters when travelling?

[Graham G3ZVT]

Originally Posted by Nickthedentist

I think the answering machine interrogator is extremely likely, or some other application which relies on a tone being sent down the phone.

Agreed.
Perhaps from this TAM I have here



although mine is 1900Hz

Incidentally the frequency generating device in the handset is not a crystal, it's a mechanical tuning fork resonator. There is a similar one in my Trio 2200G transceiver for 1750Hz