It is a completely analog battery-powered wired system that is highly resistant to electronic interception and jamming.

It can be used to transmit voice messaging in ranges between 0.3 and 3.4 kHz, with a calling frequency of 15 to 45 Hz.

Absolute signal level at output of transmission path with a 600Ω load ranges between -3 and +3 dBu.

In OB battery operation, a hand cranked magneto can be used to generate ringing.

[5] The enclosing and body is made of Bakelite and its dimensions measure 22.2 x 16.5 x 7.9 cm, and weighs 2.8 kg.