Tuning Proceedures
9
A temperature-compensated 10.000 MHz crystal oscillator provides
the frequency reference for the synthesizer. The oscillator frequency
is divided down to 25 kHz and remultiplied in the synthesizer to one of
the 256 transmit frequencies as selected by the operator via the
microcontroller. The output signal is generated by an integrated VCO.
The reference oscillator is a temperature-compensated, voltage-
controlled crystal oscillator. During manufacturing of the transmitter,
the potentiometer that sets the control voltage is adjusted so that the
reference frequency is 10.0000 MHz. This is accomplished by
adjusting a representative transmit frequency to its correct value by
means of a frequency counter. Typical frequency tolerance using this
method is +/- <0.001%.
The VCO and power amplifier operate from precision regulated power
supplies. These, and the use of close-tolerance components, fix the
output power level. During manufacture the output power level is
confirmed with a wattmeter, and adjusted when necessary by
changing the value of the resistor which biases the RF power
amplifier.
