of six bits one start bit and 5 data bits directly representing the settings of sw 2 the start bit is a 300 us pulse and the data bits are 5 width modulated pulses with a cycle length of 900 us and a duty time of either 300 or 600 us the random time generator is seeded from the 5 bit code and thus each transmitter will produce a different random sequence this ensures that the outputs of more than one transmitter used simultaneously produce only very limited interference with each other the data signal is used to switch the transmitter oscillator on and off thus producing a suppressed carrier amplitude modulation am signal at the output of the transmitter the transmitter uses a pcb track as a loop antenna tuned by c 4 frequency reference is provided by a crystal xi this oscillates at 13 56 mhz and is internally multiplied by 32 to produce a carrier frequency of 433 92 mhz when recharging power is applied to the circuit q 2 is switched on via r 7 and this in turn pulls the enable pin of the transmitter to ground disabling the rf output when charging of the battery is taking place c 5 c 6 and r 11 form a loop filter for the rf oscillator and have been selected to give a fairly.