RCA SSB-1, Инструкция

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R225 and trimmer capacitor C243 are ad­
justed to balance the output circuit of V207
to achieve a high order of cancellation of
the 250 kc signal.
e. The resultant 249 and 251 kc signals
are-applied to a mechanical filter
FL201
which operates on the magnetostriction prin­
ciple.
Its response is characterized by a
nearly flat top and a sharp drop-off on both
sides of the pass band.
FL201
resonates
with the upper sideband using 250 kc carrier
and
3.
2 kc nominal bandwidth at 6 db down.
It thus passes the 251 kc signal but elimi­
nates the
249 k
c signal. The single side­
band suppressed carrier signal is present
here for the first time: the succeeding sta­
ges are merely to heterodyne it to the de­
sired output frequency and amplify it to the
desired power level.
!_.
The 251 kc signal (upper sideband)
is then applied in opposite phase to the grids
of the 2nd balanced modulator, V206, {another
12AT7 dual-triode) along with the application,
in parallel, of an 1150 kc signal from
crystal oscillator V209. This second bal­
anced modulator operates in a manner similar
to the first one, eliminating the 1150 kc
and generating sum and difference fre­
quencies of 1401 kc and 899 kc. These two
frequencies are applied to tuned rf trans­
former T201 which passes the 1401 kc
signal but eliminates the 899 kc. Output
circuit balance is achieved by the use of
R215 and C234.
g.
The 1401 kc (upper sideband) signal is
then applied to the 3rd balanced modulator,
V205 (another 12AT7) along with the output
of crystal oscillator V208, the frequency of
which depends upon the channel crystal
selected. Assume that the highest frequency
channel is being used and that its crystal
produces an output of 15,650 kc (for a nominal
carrier frequency of 14250 kc). The 1401 kc
and 15,650 kc signals, mixed in the balanced
modulator, produce sideband frequencies of
17,051 and 14,249 kc, the 15,650 kc signal
being balanced out in the same manner as
explained for the previous balanced modu­
lators. Pretuned inductance and capacitance
circuits, selected by sections of the CHAN­
NEL switch, S201, pass the lower sideband
signal, 14,249 kc, but eliminate the 17,051 kc.
_!!.
The single-sideband signal (14,249 kc)
is then fed through the intermediate power
amplifier and power amplifier stages at
output frequency.
The IPA stage, V204,
11
uses a 6CL6 pentode in a conventional Class
A power amplifier circuit having a pretuned
inductance-capacitance network in the plate
circuit as selected by sections of the CHAN­
NEL switch, S20 1. The signal is then applied
to the grids of the power amplifiers, V20 1
and V202, (type 6146 tetrodes in parallel)
in a Class AB1 linear-amplifier circuit.
The plate circuit of the paralleled power
amplifiers is inductance-capacitance pre­
tuned to the output frequency using tapped
coil L202 and variable capacitors as selected
by the CHANNEL switch, S201. The output
signal is fed through a contact of the antenna
transfer relay, K201, and antenna loading
coil L20 1 to the antenna terminal, E204.
i . The modulator indicator amplifier
V203, (a 6BA6 pentode operating off the grid
circuit of the power amplifiers) with PEAK
MODULATION INDICATOR DS201 lamp in
its plate circuit, gives a flash indication on
the lamp when the plate current of V203
increases due to modulation peaks. This
occurs just below the point where the power
amplifier grids go positive. Necessary ad­
justment is made using TRANSMITTER
GAIN control R233 (see paragraph
Q.
above).
i·
CRYSTAL OSCILLATORS.
The three crystal oscillators, 250 kc,
1150 kc and the four-channel oscillator, are
of the electron-coupled type with crystals
connected between screen and grid, output
being taken from the plate circuit. Each
oscillator supplies mixing frequency for both
the transmitter balanced modulator and the
receiver mixer stages. Crystals are mounted
in dual crystal ovens of the plug-in type. The
oven heaters are fed 6.3 v ac from trans­
former T 104.
The 250 kc o s c i l l a t o r, V210, uses a
6BE6 pentagrid tube and the 250 kc crystal,
Y206, is mounted in oven E203.
The 1150 kc oscillator, V209, also uses
a 6BE6 pentagrid tube and the 1150 kc
crystal (Y205) is also mounted in oven
E203. SPEECH CLARIFIER capacitor C268
varies the oscillator frequency over a small
range so the operator may bring the frequency
exactly to that of the station he is working.
The channel frequency oscillator (V208)
uses a 6CL6 power pentode and any one of
four crystals (Y20 1 to Y204) as selected by
CHANNEL selector S201. Diodes CR201 and
CR202 keep the output voltage of V208 at a