Wireless Telegraph Set 120 Watt

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W/T Set Field 120 watt CW
Marconi 120 watt set (2).jpg
Production history
Introduced 1918
Manufacturer Marconi
Length 4 ft 7 in
Width 2 ft
Height 2 ft 4 in

450-8000m Receive
600-2200m Transmit (Mk I)
600-3500m Transmit (Mk I*)
120 watts
Range 60 miles
Wireless Telegraph Set 120 Watt CW was a set designed for use down to and including Divisional Headquarters level. It consists of a sending and receiving instruments wired up in a case with a roller desk front. In addition, secondary batteries, aerial and earth are required for operation.[1]

WT Set 120 Watt Case

The main components fitted in the WT Set 120 watt Mk I* case were:

Ammeters, HF, 2-amp
Amplifiers, C, Mk IV* (without case)
Keys, WT, 10-amp, No. 1 or Keys, S.C., W.T
Senders, 120-watt Mk 1*
Switchboards, 120-watt, Mk I*
Transformers, rotary, H.T., 150-watt
Tuners, 120-watt set

In addition, were various inductances, resistances, a rheostat, earth sockets and condensers.

The Mk I differed in that it had a Converter 120 watt (instead of the transformer), a Key, WT 10 amp. No. 2, a switchboard Mk I and included a rectifier.

Complete Station

A complete station weighed 1,630 lb (740 kg) and was composed of the following items:

Item Size Weight
WT Set 120-watt 4 ft 7 in x 2 ft x 2 ft 4 in high 210 lbs
Case spare parts No.1 (Mk I)
Case spare parts No.2 (Mk I*)
20 x 19 x 12 in 20 lbs for Mk I
105 lbs for Mk I*
2 cases mast gear each 4 ft x 1 ft 4 in x 1 ft 320 lbs
1 case aerial gear 27 x 16 x 9 in 20 lbs
16 mast sections each 8 ft 9 ins long 320 lbs
2 spreaders each 10 ft long 10 lbs
Batteries - secondary portable 6-volt 100/125 a.h.
10 for Mk I, 8 for Mk I*
each 13 x 12 x 8 in 530 lbs for Mk I
425 lbs for Mk I*
Mauls and pickets   20 lbs

In addition a Generating set 1 kw (or 1.5 kw), 50 volt charging was used to charge the batteries. It was 4 ft 6 in x 3 ft 1 in x 3 ft 1 in and weighed an additional 335 lbs. For fixed sites, 22 6-volt 16 a.h. batteries could be used in lieu of the primary batteries with an approximate additional weight of 400 lbs.

Canadian Use

In Canada, WT 120 Watt Sets were used to communicate between the R.C.A.F Training Depot at Camp Borden and Rockcliff (Ottawa) in the early 1920s. In addition, early wireless sites of the Northwest Territories and Yukon Radio System were equiped with WT 120 Watt sets.

Related Pages

Related Items


  1. Signal Training Volume III, Pamphlet No. 6, Description of and Instructions for Wireless Telegraph Set 120-Watt Mark I*, 1925