INTRODUCTION These receivers have been designed to fully comply with the ‘Performance Specification for al Purpose Receivers for Merchant Ships’ as laid down by the General Post Office. The two receivers together cover the frequencies from 15 kc/s to 25 Mc/s. Each receiver has five and on the ‘Mercury’, type 1017, the frequencies of these ranges are:—15 to 40 kc/s, 100 to 250 250 to 640 kc/s, 640 to 1,600 kc/s and 1,600 to 4,000 kc/s. On the ‘Electra’ type 1018, the ncies of these ranges are:—250 to 520 kc/s, 1.5 to 3.0 Mc/s, 3.0 to 6.0 Mc/s, 6.0 to 12.0 Mc/s 2.0 to 25 Mc/s. Both receivers are designed to work from a type 889A power unit which will operate off 24, 110 20 volts D.C. and 230 volts A.C. The type 889 power unit may also be used with both these ;rs. Special features of both receivers include the following: —A high degree of electrical and thermal ty is ensured by the provision of a voltage stabilizer and a temperature compensator. A high-nination log scale is fitted to each receiver to supplement the normal frequency calibration. The ;r type 1018 also includes a set of bandspread scales to expand each of the six H.F. shipping ; when used in conjunction with the built-in crystal calibrator these scales permit the accurate ning of a hitherto unlogged station, knowing only the frequency of the latter. Four degrees of selectivity are provided with bandwidths ranging from 8 kc/s to 150 c.p.s. circuit refinements include an automatically controlled pulse limiter. Protection is afforded against possible damage of the receiver circuits from an associated trans-by the inclusion of high speed relays which can be operated by the back contacts of the jitter key.