CIRCUIT FOR SUPPLYING AN AMPLITUDE MODULATED CURRENT TO AN R.F. STAGE OF A RADIO TRANSMITTER

摘要

In pulse width modulation circuits for supplying amplitude modulated current to the anode of the R.F. stage of a high power radio transmitter, problems arise from carrier compression and from the need to protect the voltage source against excessive currents in the event of one or both of the switching valves breaking down. The protection circuit needs to handle an extremely large power: namely all the power supplied to the anode. The invention overcomes this problem by using two voltage sources (1, 9) one (1) of which provides carrier power whilst the other (9) drives a pulse width modulation amplifier (8) which modulates the carrier. Varying demand for power to the amplifier (8) thus does not effect the carrier. Therefore carrier compression is reduced. Also, only that voltage source (9) which feeds the amplifier needs a sophisticated fast acting protection system (11, 12) and since this does not supply all of the power to the anode the protection system is able to operate reliably.