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Aviation History
1950
1950 - 0117.PDF
Romac Model 160 R/T and navigation installation for a Rapide. range from a single- -to a six-channel set. There are two sets with a greater number of channels—one with eleven (Ekco CE 40) and the other with 23 (Murphy MR 80)— which might be regarded as outside the scope of private users. In operation one channel may be set up on the universal guard and the others on the common approach and airfield-control frequencies. These frequencies will still be guarded even when the multi-frequency plan is implemented so that the smaller sets will not become obsolete. Typical of these sets is the Murphy five-channel MR 60, which consists of a basic transmitter/receiver unit, which can be stowed away in the fuselage, and a controller for mounting near to the pilot. This control unit contains the crystals for transmission and reception, the channel-Selec- tion switch, volume control and on-off switch. All that is necessary to change channels is to turn the selector switch. Additional frequencies can be set up by inserting the appro- priate crystals, no lining-up being necessary, as it is pre-set. The power output is i£ watt, which should be adequate for ranges up to 50 miles or more (depending on altitude) and the receiver sensitivity is high enough for two-way communication at these ranges. Power consumption is 100 watts. The transmitter/receiver unit fits into the standard R.C.E.E.A. racking and the complete installation, includ- ing aerial, headset, microphone and interconnecting cables, which are all supplied, weighs approximately 20 1b. If the aircraft is not already screened it will be necessary (Below) Twin-channel Ekco set with control box and headset. (Right)Rear connections of the 4-channel (2 twins) V.H.F. T.R. Model CE 17/24. Ekco control box mounted in a Proctor instrument panel. to fit a new ignition harness to avoid interference. On some aircraft the magnetos may have to be replaced by a screened type. These items are not normally supplied by the set manufacturer but by the firm carrying out the installation. Another interesting set is the Plessey six-channel PTR 61. In this, changing from one channel to another requires two operations, selection of the channel required and tuning-up. The latter operation is extremely simple, as a tuning meter is incorporated in the main unit or in the remote controller (if fitted). It is only necessary to depress the spring-loaded tuning knob and turn for maximum read- ing. The same procedure applies if crystals for other channels are inserted. If the set is mounted in the instru- ment panel, as will often be the case, crystals can be changed in flight. A feature of the Plessey set is the low consumption in the receiving position, namely, 55 watts. Ranges up to 78 miles have been recorded. The Ekco CE 17 and CE 17/24, two-and four-channel sets, have been in production for some time and are fitted to some 400 aircraft. Their CE 40 is an eleven-channel set with an average power consumption of only 50 watts. A complete installation weighs about 29 lb. Standard Telephones and Cables produce the STRa. which has now been modified to provide ten channels, and the STR12 with 23 channels. These, in a rather different class, are more expensive than others described' here. The use of MF for communication purposes is giving
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