Heathkit SG-8 Assembly And Operation Manual page 3

INTRODUCTION
and easy to use. This generator has been engineered so that t wi
ham and experiment ange of uses. in additio
im aaaiio
pair man, nam ana experimer nte
highly dependable piece e of test equ
nge Va MOUS,
is made with high quality parts, conservatively
ang and effi
rated, and will give long andeffici
adjusted coils, thereby eliminatin
wmanten ~ Sant im ie brate the finished kit.
patater| Th
ipment. It
+
service. The model SG-8 Signal Generator utilizes factory
he necessity of having costly equipment available to cali-
ga om +
CIRCUIT DESCRIPTION
thereby m maki ng it a closed circuit inductance which is capable of tuning from 25 to 100 mega-
r necessary to maintain oscillations is obtained from a
nce
y ai
Cc of the frequency determining circuit. In the
d by the use of a split-stator condenser. The ad-
v i
apparent from the following explanation. For example, take a ca-
f
capacitive reactance divider across t
model SG-8, a capacitive divider
vantage of this will be made
pacitive divider composed of fixed capacities. As the frequency across the condensers is in-
creased, the reactance
of the condensers is decreased.
Therefore,
using a fixed capacitive
divider, as the frequency is increased reactance would become lower until a point was reached
where
oscillations could no longer be maintained.
By the use.of a split-stator condenser for
both tuning and as the divider network
as the frequency is increased,
the capacity of the con-
denser dividing network is decreased.
The reactance of a condenser for any given frequency is
inversely proportional tothe capacity. This
tendsto maintain
the reactance of the network fair-
a +
t=] U Ll
ly constant, thereby permitting oscillation over a wide range 0
The use of the cathode follower as a buffer stage has the following advantage: The characteris-
tin £ Ai thinAn Frill ial
tics of a "cathode follower" are very low output impedance with an extremely high input imped-
ance. The extremely high input impedance produces little or no loading onthe oscillator circuit .
The very low output impedance provides a very stable output from the signal generator. The
effect is such that a varying load on the output of the signal generator will produce little or no
frequency instability of the oscillator.
The signal generator incorporates a Step attenuator for
coarse control of radio frequency output afd a continuously variable attenuation circuit for fine
control of the radio frequency output.
The audio oscillator is also a Colpitts circuit. By the use o large
core choke and relatively high capacity in the capacitive divider, it is made to "oscillate a
proximately 400 cycles. This type of oscillator was again chosen for its stabili
waveform. With the modulation switch in the INT. position, 400 cycles audio voltage is ap-
plied through a resistance network to the grid of the cathode followers Stage. This audio vo tage
t fro
is impressed as an amplitude modulated signal upon the RF output
At the same time the audio voltage is also applied to the external audio ccnne 'tor marked CUT,
and may be used as an audio signal source for testing amplifiers, etc. Wich the modulition
switch in the EXT. position, any external audio source of any frequency may be used to modu-
late the RF output of the signal generator. The 6C4 audio oscillator tube then becomes an am-
plifier stage for the external signal.
Page 3