LOOP AERIAL OPERATION

Radio Record, Volume I, Issue 42, 4 May 1928, Page 12

LOOP AERIAL OPERATION

------- TWO SUITABLE CIRCUITS N furtherance of the article on loop aerials given last week, two circuit diagrams are shown suitable for frame acrial operation. R.F. amplification is not an absolute necessity in loop operation, but it is necessary that all unnecessary R.F. damping be eliminated. The Browning-Drake circuit is not very suitable for frame aerial operation. | REINARTZ REACTION.

V ITH the tuning condenser across part only of the inductance, we get the Reinartz type of reaction, which has proved to be so effective in ordinary selective reception with outside aerials. Here a fixed reaction coil is wound continuously with, and in the same direction as, the main tuning inductance, either on to the same former or closely adjacent so as to Le close coupled magnetically with the first. In other words, two or three turns of the loop are utilised to secure reaction. This is fed via a small variable reaction condenser from the anode of the detector valve, the high-frequency impulses being prevented by an efficient radio choke from passing to "earth" via the distributed capacity of the phones or transformer windings and H.T. battery in mcdern versions of the circuit. The reaction control is then carried out entirely by this small condenser; and with proper design of the circuit and with low-loss inductances it is of an extremely fine and, at the same time, manageable type. The number of

turns required in the reaction coil is surprisingly small with valves of high amplification value and liberal electronic emission. The reaction condenser can be of low maximum capacity: .0001 mfd., the usual troublesome change in wavelength, with alteration of reaction coupling is then almost entirely avoided over the small range necessary for. fine adjustment; whilst the reaction demands vary but slightly with frequency over the whole tuning range. This greatly facilitates ‘‘searching"’ in practice. A "super" circuit for loop operation will be given later. PUTRI OTA ANORORUNTHR URAHARA HHUA M RMT

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