|
Here's a circuit that allows one to drive a Class D push-pull amplifier with the output from a linear transmitter or transverter. It should be noted that this is only usable for frequency modulated modes such as RTTY, Pactor, Amtor, MFSK, Olivia, Domino, Throb, WSJT, WSPR etc. It can not be used with amplitude modulated signals such as PSK, BPSK, QPSK, WOLF etc.
X2LinearClassDinterface.pdf
The circuit is a frequency doubler that provides the required Class D drive at two times the final output frequency. Supply a 505 kHz carrier at the input and get a 1010 kHz carrier at the output. The modulation (or frequency shift) is also doubled ... which is exactly what is required. The input to the Class D push-pull amplifier utilizes a flip flop (divide by 2) that provides the two phases to drive the push pull arrangement. This divide by two restores the proper frequency shift.
The hybrid analog/digital circuit makes use of a diode ring mixer as a frequency doubler. This device was chosen in lieu of digital doubler circuits as they can be finicky with regard to duty cycle. Following the diode ring mixer is a 74HCT4046 that squares up the signal and this feeds an IR2110 driver. No doubt there may be other ways to accomplish this task but all components were available within arms reach while piecing it together on the bench!
The input to the multiplier should be in the -3 to +10 dBm range. If the drive level is in excess of +10 dBm consider adding an attenuator between the output of the transceiver / transverter and the input to the doubler.
|