Heathkit SB-401 - LSB-USB-CW CARRIER GENERATOR AND CATHODE FOLLOWER

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Figure 6-5
LSB-USB-CW CARRIER GENERATOR AND
CATHODE FOLLOWER (Figure 6-5)
V2A and V2B are Colpitts type crystal oscil-
lators, The setting of the Mode switch determines
which of these tube sections will be in operation,
This is done by switching B+ tothe desired gen-
erator, and also selecting the proper frequency
crystal for V2B,. V2B serves as the USBand CW
carrier generator, and V2A serves as the LSB
carrier generator,
The output of the carrier generator is coupled
through capacitor C126 to the grid of cathode
follower V2C, Sideband Amplitude Balance con-
trol R123 is adjusted for equal USB and LSB
output by slightly lowering or raising the B+
voltage on V2A, This adjustment is not critical
and a preset value is sufficient,
For transceiver operation in the CW mode,
the receiver must be tuned one kilohertz above
the frequency of the received CW signal, thus
producing a 1000 Hz beat note, If the trans-
mitter
and
the
receiver
were
tuned
to
the
same
frequency,
as
in
normal
transceiver
op-
eration, no beat note could be heard, With the
receiver tuned 1000 Hz above the received sig-
nal, the transmitter CW carrier generator auto-
matically compensates and transmits a signal
1000 Hz below the receiver dial setting, This
allows the transmitted and received signals to
be on the same frequency, yet allowing the
receiver to produce an audible tone,
For transceiver operation in either USB or LSB
modes, the carrier generator in the Transmitter
is inoperative on both transmit and receive
modes, The required carrier generator signal
for both transmit and receive is obtained from
the receiver BFO, On transmit, the BFO re-
ceiver signal is coupled through capacitor C127
to the grid of V2C, Cathode follower V2C is an
impedance matching stage for the low input
impedance of the balanced modulator,