450Khz signal generators

Last updated: January 29, 2021

450 KHz AM modulated signal generators. The digital version has been used to repair an old tube radio. It's the only version with protection agains high voltage spikes, e.g. plate voltage, on the output.

Analog version 1


Single Li-ion cell Vrf = 400 mVtt Vlf = 1.2 Vtt	Single Li-ion cell Vlf = 1.4 Vtt

Analog version 2


Single Li-ion cell Vrf = 3.5 Vtt Vlf = 0,379 Vrms	Single Li-ion cell Vlf = 0,4 Vrms

Digital version


Single Li-ion cell Flf = 600 HZ	Single Li-ion cell

AM modulation is done by varying the duty-cycle of the output signal. The 1k2 and 2k2 resistors, the 330p capacitor and the last invertor form a rudimentary pulse-width modulator. The duty-cycle varies between 20% en 55%. When used in a circuit there's always the risk of voltage spikes on the output. The 1N4148 diodes and the 1k output resistor limit the voltage on and the current into pin 6 of the 74HC04 to safe values. For use in tube circuits the probe is used.

Microprocessor version

The microprocessor version is a software DDS with modifications for AM en FM modulation. The development version runs on a Arduino Uno R3.

Downloads

Archive Containing sources for the micropocessor version.