GAREX TWOMOBILE MK II, Руководство по эксплуатации

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D R A F T D R A F T D R A F T
Garex Twomobile 5 Handbook
RF Unit
The antenna changeover relay contacts RLA1 connect the aerial input to the
RF amplifiers VT1, VT2 which are coupled to the FET mixer VT3 by the tuned
circuit L4. The local oscillator frequency is generated by a temperature
compensated FET variable frequency oscillator having a 2MHz tuning range.
Buffer stages, including VT4, isolate the wanted frequency. The output from
VT3 is the first IF of 10.7MHz.
1st IF Unit
VTI01, VT102, VT103 are transformer coupled cascade amplifiers at 10.7MHz.
The output is coupled by transformer T104 to the second mixer VT203.
2nd Mixer Unit
The mixer FET VT203 combines the 10.7MHz first IF with the l0.245 MHz
output from the local oscillator VT202, producing the 2nd IF of 455kHz,
which passes through a single stage amplifier VT2O1 to the 455kHz bandpass
filter.
455kHz Bandpass Filter
This filter is a sealed unit which determines the selectivity of the
receiver. The bandwidth is 10kHz (±5kHz) which allows a good compromise
between selectivity and satisfactory resolution of frequency modulated
signals with a peak deviation of up to ±3kHz.
2nd IF Unit
The output from the bandpass filter is coupled to the two amplifying stages
VT302, VT303 and emitter followers VT301, VT304. When receiving amplitude
modulated signals a third amplifying stage VT305 is used. Transformer T302
in its collector circuit has two secondary windings, which are connected
respectively to the signal detector MR302 and the AGC detector MR303. The
rectified output from MR303 is fed back via emitter follower VT306 as AGC
bias to the RF stages VT1, VT2, and the IF amplifiers VT302, VT303.
The rectified output from MR302 passes through the noise limiter MR304 the
receiver mode selection switch (S2).
Frequency modulated signals are taken from the emitter of VT304 to the
input of the quadrature detector IC402. The audio output from IC402 is
taken to S2. Audio then passes to the emitter follower VT307 and the
squelch diode MR305.
Squelch Unit
VT40l is a switching stage controlled by the AGC bias level. Under no
signal conditions VT401 maintains the cathode of MR305 at a level less
negative than its anode, which is controlled by VT307, thereby MR305 is
prevented from conducting. When a signal is received the AGC voltage
becomes less negative allowing MR305 to conduct and permit the audio to
pass to the volume control and audio amplifying stages. The setting of VR1
(located on the front panel) determines the emitter voltage of VT401, and
thus the level at which the squelch operates.
AF Section
The AF from the volume control VR2 (located on the front panel) is
amplified by VT503 and coupled via the emitter—fo1lower VT501, to the
driver VT505. Phase splitting transformer T502 in the collector of VT505
drives the push—pull output stage VT505, VT507. T503 is the loudspeaker
output transformer.