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 Post subject: 8 channel crystal controlled AM broadcast transmittet
PostPosted: Sep Wed 22, 2021 5:26 pm 

Joined: Mar Thu 01, 2018 1:30 am
Posts: 839
Bit switches S1 to S8 covers eight different MW radio frequencies. Number of crystals required is five. A single 2n3904 colpitts oscillator should drive the divider IC CD4040 as its CLK input is biased at half the supply voltage. The 2n3904 output voltage swing should be enough to trigger it. A ferrite rod with untuned primary and tuned secondary will decide the performance of this circuit. It's part 15 compatible as the DC input power to the pushpull mosfet amplifier should never exceed 100mW with no audio present. The inout impedance of 2n7000 is around 3K at 1.5MHz so a CD4013 easily drive the pair. The symmetrical drive maintains output symmetry of upper and lower side bands and great sounding audio. The pushpull arrangement attenuates even order harmonics which is an added plus point.

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