2. Transmitter Circuit
IC202 (PLL—LSI), VCO section of IC204 (pins 1,2, and 3) are
operational regardless of the receive or transmit mode. When
the radio is set to the transmit mode, mixer/amplifier section
of IC204 (pins 4,6,7 and 9), Q203, Q301, Q302 and Q303 are
activated. The VCO frequency selected by the channel selector
switch is mixed with 10.24MHz to generate desired transmit
frequency. The mixing is done by a mixer circuit located inside
the IC204•
The resulting transmit frequency from pin 9 of IC204 is filtered
by L301 and L302. Q301 is an amplifier/switch circuit. When
VCO frequency is out of "LOCK" condition pin 14 of IC202 pulls
down bias voltage of Q301 to ground disabling Q301 from passing
possible illegal frequencies. Q302 is a RF power driver circuit
and Q303 is the final RF power amplifier.
A modulation audio signal is applied to the collectors of Q302
and Q303 through an audio power transformer T501. The audio
signal (mic input) is amplified by a single power IC501. The
modulation limiting is accomplished by an automatic level
control circuit which is as follows:
L305 and C317 are sériés résonant , and RFC303, L306, RFC304,
C321, 322, 324 and C326 make up PI-LOW pass filter. C312 is
factory selected and limits the RF output level to within the
FCC limit of 4 watts.
19 PLUS -3-
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