Wireless Telegraph Set Forward Spark 20 watt B
The Wireless Telegraph Set Forward Spark 20 watt B, also known as the Loop Set, was a spark telegraphy set used for forward area communications. The complete set was comprised of a Front and a Rear Station, the equipment not being interchangable. There were three versions produced, a Mk I, I* and II with only minor details different between them. 
The Rear Station consisted of a transmitter and a receiver, either a 50 ft (65 metre version) or 60 ft (80 metre version) horizontal wire on two 4 ft folding tripod supports and a 14 ft earth net.
The Front Station consisted of a transmitter with a collapsible loop aerial 1 metre square and a receiver with a ground aerial consisting of two 35 ft insulated wires to be thrown out on the ground in opposite directions. The 1 metre square transmitter aerial was made of 3/8 inch brass tubing and was mounted on a small ebonite box (5 1/2 x 2 1/2 x 1 1/2 inches) that contained the transmitter spark gap. Fitted on a service bayonet, the unit was driven into the ground. The operator could be 20 feet away connected by a flexible cable to the second transmitter unit compromising an induction coil and Morse key.
- Wireless for the Warrior Compendium 1. Louis Melustee. Emaus, 2009. ISBN 978-90-808277-2-1