The Model SG-83 Standard Signal Generator is a laboratory
test instrument which generates accurately known r-f
voltages in the 360 kc to 30 me range. Either unmodulated or
modulated signals may be obtained. This instrument makes
possible for the first time at moderate cost accurate
laboratory measurements which are essential in communication
circuit development and testing.
Because of its accurate output voltage calibration, the
SG-83 can be used to make quantitative r-f signal
measurements. This signal Generator should not be confused
with the common signal Generator which provides only a
source of signals of unspecified level or modulation
characteristics. With the SG-83, laboratory measurements may
be made which previously required much more expensive
industrial equipment not usually available to individuals.
The SG-83 signal Generator will produce signals of 0.6
microvolt to 16,000 microvolts, accurate to approximately 1
db or + 10%. The output signal is calibrated directly in
decibels with zero db equal to one microvolt across a 50 ohm
load. Other levels up to -I- 84 db (16,000 microvolts) are
obtainable with the switch attenuator and meter. On the
front panel of the instrument is a chart to facilitate rapid
conversion from microvolts to db and vice versa.
The r-f signal is generated by a high-frequency transistor
oscillator. The power level of the Oscillator is maintained
at a level just sufficient to be metered on a panel
microammeter to reduce the strength of leakage fields. The
transistor r-f Oscillator gives excellent frequency
stability since there is none of the long warm-up drift
common in vacuum tube oscillators. The output is extremely
flat over the frequency ranges. Variation in Oscillator
output over any one band is normally less than 1 db. It is
not necessary to readjust the output attenuator continually
as the Generator is tuned over a wide frequency range, which
is a definite convenience in operation.
Output from the transistor Oscillator is applied to a
constant input impedance variable attenuator which is
adjusted by a front panel control. The attenuator is
designed to produce very little change in loading on the
Oscillator as the attenuation is varied, to minimize effects
on the frequency of the Oscillator.
The Oscillator has a fine tuning control which is useful in
varying the frequency in small increments or recalibrating
the main tuning dial against an external Frequency Standard.
The fine tuning control is calibrated from + 2.5 to - 2.5 Kc
when the main tuning dial is set to 455 Kc. This permits
small frequency changes to be read directly when making
response curve tests at the commonly used i-f frequency.