Date of Design : 1926

Frequency range: N/A

Fitted into D/F Outfit SD

Quote.....G21 is a buzzer tester for D/F and was introduced to meet the need for an instrument which could be made to influence each loop aerial to exactly the same extent. If the two loops are identical [as in shore D/F stations] and are equally energised the zero will be found to be at Green 45˚. In a ship where the fore and aft aerial is usually smaller than the beam aerial the zero will be found to be nearer the bow at about Green 30˚.  Unquote.