Crown Low Power Transmitters - Crown Broadcast
Crown Low Power Transmitters - Crown Broadcast
Crown Low Power Transmitters - Crown Broadcast
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4.4 RF Exciter Circuit Board<br />
This board is also known as the Frequency Synthesizer board. The entire<br />
component side of the board is a ground plane. Frequency selector switches along<br />
the front edge of the board establish the operating frequency. The VCO<br />
(voltage-controlled oscillator) circuitry is inside an aluminum case.<br />
Illustration 6–7 and accompanying schematic can be used as reference in this<br />
discussion.<br />
VCO61 operates at the synthesizer output frequency of 87 MHz to 108 MHz.<br />
The frequency is controlled by a voltage applied to pin 8 of the VCO.<br />
A sample of the RF comes from A2 and is fed to the PLL chip U6.<br />
U304 is a phase-locked-loop frequency synthesizer IC. The 10.24 MHz from the<br />
crystal oscillator is divided to 10 kHz. Internal programmable dividers divide the<br />
87 - 108 MHz RF to 10 kHz. Differences between the two signals produce error<br />
RF<br />
Exciter<br />
Board<br />
®<br />
FM250<br />
4–6 FM30/FM100/FM250 User's Manual
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