Sailor RE2100, Техническое руководство

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5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RE2100
PAGE 5-18 9324
PRESCALER BUFFER
From the oscillator buffer transistor Q36 the signal is fed through the network consisting of R159 and C180
to the grounded basis transistor Q38. The local oscillator signal is amplified here and fed through the
attenuator R168/R170 and the amplifier transistor Q40. The result is an amplitude stabilized signal which
is fed to the prescaler U36.
PRESCALER AND DIVIDER
The programmable divider consists of a dual modulus divider U36, dividing by 32/33 and a programmable
divider included in U35.
The division ratio is determined by the number latched into U35 and together with U36 the divider works
as a conventional dual modulus divider with the modulus control from U35 controlling the prescaler U36.
The reference frequency divider is included in U35.
The reference frequency input on pin 1 has the frequency 5,365.760 MHz and the reference division ratio
R read into U35 is 131 leading to a reference frequency of 40.96 kHz which can be monitored on pin 13.
This 40.96 kHz signal is used as the reference signal to the phase detector. The variable frequency to
the phase detector is the VCO frequency divided with the read in “division ratio”. This ratio is 1447 when
USB mode is chosen, and by LSB mode 1971 leading to the two phase lock frequencies in USB of
59,269.120 MHz and in LSB mode 80,732.160 MHz.
PHASE DETECTOR AND LOOP FILTER
The phase detector is an integrated part of U35. The input reference frequency f
R
is 40.96 kHz which can
be monitored on pin 13 and the input variable frequency f
V
can be monitored on pin 3. The three-state
output of the phase detector produces a loop error signal which is used with the loop filter to control the
VCO. The phase detector output is for frequency f
V
> f
R
or f
V
leading, negative pulses. For frequency f
V
< f
R
or f
V
lagging, positive pulses and for f
V
= f
R
and phase coincidence, the output is in high impedance
state.
The loop filter consists of two parts. The first part of the loop filter built around the amplifier U34 and the
R/C network R118 and C131 take care of the loop characteristic. The second part of the filter consisting
of L34, L35 and C141/C143/C146 is a passive lowpass filter which removes the remaining part of the
40.96 kHz reference signal from the VCO control signal.
OUTPUT LOCAL OSCILLATOR BUFFER
From the oscillator buffer transistor Q36 the VCO signal is amplified in transistor Q34 and filtered in the
lowpass filter consisting of C176, L40, and C177. Before the signal is fed to the output terminal it is
amplified in transistor Q37 and fed through the relay RE2.
When the relay is activated the VCO signal is fed into the first mixer on the transmitter module. The diode
D26 is conducting and thereby grounding the remaining part of the signal to the receiver module. When
the relay RE2 is not activated the diode D26 is reversed and the VCO signal is fed to second mixer on
the receiver module.