SBE SB-36 OPERATION MANUAL
5. 2 TRANSMITTER CIRCUITRY
5.2.1 Transmitter Signal Path
Stage-by-Stage transmit signal path block diagrams is shown in Figure
5.1. Unless otherwise indicated in the following explanation, it is
assumed that the SB-36 is operating in the Single Sideband Mode.
Audio signals from the microphone connector or phone patch input jack
are routed to TR-l located on the Microphone Amplifier and Side Tone
Oscillator Board. The audio signal is amplified by transistor TR-l and
then routed to the base of TR-2. The amplified output of transistor TR-2
is routed through transistor TR-3, which is operating as an emitter
follower. The output of transistor TR-3 is routed through variable
resister VR-l (Microphone Gain Potentiometer) to the base of transistor
TR-4.
The signal from transistor TR-4 is then routed to one input of the
balanced modulator. The balanced modulator is comprised of
transformer T-9 and Diodes D-1 through D-4. The second input of the
balanced modulator is a 9.0 MHz carrier signal. The 9.0 MHz carrier
signal originates in the carrier oscillator board and is applied to the
balanced modulator by variable resistor VR-5. The balanced modulator
mixes the 9.0 MHz carrier with the audio signal to produce a resultant
9.0 MHz double sideband signal with a carrier suppressed
approximately 40 dB. Third and higher order modulation products are
also suppressed approximately 30 dB below each sideband. The
balanced modulator output is routed to the input of the upper or lower
sideband crystal filter.
The output from the crystal filter is routed by transformer T-10 to the
input of transistor TR-7. The output of transistor TR-7 is coupled by
transformer T-11 to the grid of mixer tube V-1.
A second input to the grid of mixer tube V-l is derived by mixing the
output of the HFO transistor TR-10 with the output of VFO oscillator.
The HFO oscillator output and the VFO oscillator output are combined
in mixer transistor TR-11. The resultant frequency is transformer
coupled to the grid of mixer tube V-1.
The desired transmit frequency is obtained by mixing the 9.0 MHz
sideband output of transistor TR-7 with the HFO/VFO product produced
NoobowSystems Lab. Tomioka, Japan 2003 http://www.noobowsystems.com/ Page 21 / 56
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