2. Transmitter System
1) Main Unit
a. Microphone Amplifier
The input signal from microphone is amplified by the low noise amplifier 056
through the mic gain VR1. It is possible to bias (8V) the microphone terminal with
R388 for the microphone which needs the power supply, (solder bridge)
In SSB/AM mode, The gain of IC21 (approx. 15dB) is determined by R329 and
R328.
In FM mode, R330 is connected to R320 in parallel by Q55, then the gain is
increased approximately 34dB. Also the cut off frequency is risen, and the signal
is pre-emphasized and operated as a limitter.
In the SSB/AM mode, C345 and R384 are conntected to the feedback circuit by
Q63 when the speech compressor is turned ON. The gain is increased about
15dB, then IC21:B is operated as the limitter.
When the speech compressor is ON, the low frequency is cut by C345.
In FM mode, the gain is risen enough, so the speech compressor has no effect.
The output of Pin1 of IC21: B is attenuated in R326 and R325. The subaudible
tone from PLL unit is applied through R325. (When the Tone is ON.)
IC21: A is LPF amplifier that is the Splutter filter in FM mode, and it is operated for
speech compressor.
This signal is output to PLL unit as the FM modulation, and output to the balanced
modulation of IC2.
The output to IC2 is muted by Q54 in CW/FM mode.
b. Balanced Mixer
!C2 is the balanced mixer, and the carrier is suppressed in SSB mode. To get
more ratio of carrier suppression, the balance adjustment of VR3 and VR4 are
applied.
The carrier is necessary in CW/FM/AM mode, so the input of Pinl is made unbal
anced by applying the DC voltage to obtain the carrier.
By applying the DC in AM/FM mode, or by keying in CW mode, the balance is
broken to obtain the carrier wave. VR11 is used for the adjustment of carrier level.
In the AM mode, the DC and modulation is added simultaneously. In SSB mode,
the modulation is added by R317. In AM mode, D93 is DC-biased and turned ON.
Then the attenuator consisting of R317 and R393 limits the modulation.
c. IF Filter
After the output of !C2 increases the impedance in C177 and L77, it is passed
through D49 and led into band limit IF filter. D52 is isolated highly by connecting to
the output in parallel at receiving. In SSB mode, the output is DSB signal. (Double
Side Band)
The filter is switched by the selection of above-mentioned diode switch. The signal
is passed through the following filer in each mode.
SSB FL3(CFJ455K5) 2.4kHz/-6dB 4.5kHz/-60dB
CW FL2 (CFJ455K8) 1.0kHz/-6dB 3.0kHz/-60dB
FM, AM FL4 (CFW455G) 9kHz/-6dB 20kHz/-50dB
SSB is obtained by eliminati'ng one of side bands of DSB through the filter.
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