2008-10-11
Circuit Diagrams for the AM Walkie-Talkie Experiments
A lot of people have asked for the circuit diagrams for this experiment, so here they are...
TX
The 7 turn link output is resonated with 47 pF to get reasonable power out, but it is still quite a feeble transmitter.
RX
The coil for the detector is described in the original article
Higher Q filters might be better, but these work and are very simple, using the same R and C values - which might be considered a feature.
Comments
To make a full transceiver you'll need a microphone amplifier and probably a loudspeaker amplifier although the output of the AF filter board drives a xtal earpiece just fine and small low-impedance headphones to some degree.
You'll probably want more output TX power, the design delivers about 2 mW PEP! You might consider collector modulating another RF stage driven by the xtal oscillator instead of the oscillator itself.
Design supply voltage is 9 volts.
The xtal case is grounded in the TX. Ungrounded the amplitude modulation linearity is effected - I am not completely sure why.
4 comments.
Parent article: AM Walkie-Talkie Experiments.