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output impedance, thereby minimizing signal reflection or
power loss on the line due to impedance mismatch.
MODEL 180
RECEIVING
INSTRUMENT
OUTPUT
IMPEDANCE
5on
OUTPUT
RG58 OR
EQUIVALENT
50r2
LOAD,
EFFECTIVE
CIRCUIT
RESISTANCE
-AAA^
1
1
(SIGNAL
LOAD)
V.
Figure 3-4. Signal Termination
The input and output impedances of the generator con
nectors are listed below:
Connector
50S2 OUT HI
50^2 OUT LO
PULSE OUT (TTL)
SWEEP OUT
VCG IN
GCVOUT
Impedance
50^2
son
60on
2kn
60on
•The PULSE OUT connector can drive up to 20 Transistor-Transistor
Logic (TTL) loads (low level between OV and 0.4V. and high level
between 2.4V and 5V).
3.2.2
Manually Controlled Operation
For basic operation, select the waveform to be output, and
set the output signal frequency and amplitude. The following
steps demonstrate manual control of the function generator:
Step
Co ntrol /Co n nector
1
50n OUT
2
FREQMULT
3
Frequency Dial
4
Waveform Selector
5
DC OFFSET
6
AMPLITUDE
Setting
Connect circuit to either
HI or LO output (Ref:
paragraph 3.2.1).
Set to desired range of
frequency.
Set to desired frequency.
Set to desired waveform.
See figure 3-5.
Select desired amplitude.
TRIANGLE
WAVEFORM
FROM HI OUTPUT
INTO 50I2 load
•f6V
OV
-5V
GDC
OFFSET
POSITIVE
DC OFFSET
NEGATIVE
DC OFFSET
+5V — n—
EXCESSIVE
POSITIVE
OFFSET OR
LOADING
EXCESSIVE
NEGATIVE
OFFSET OR
LOADING
Figure 3-5. DC OFFSET Control
3.2.3
Voltage Controlled Operation
Operation as a voltage controlled function generator (VCG)
is as for a manually controlled function generator, only the
frequency within particular ranges is additionally controlled
with dc levels (±2V excursions) injected at the VCG IN
connector. Perform the steps given in paragraph 3.2.2, only
set the frequency dial to determine a reference from which
the frequency is to be voltage controlled:
1.
For frequency control with positive dc inputs at
VCG IN, set the dial for a lower frequency limit.
2.
For frequency control with negative dc inputs at
VCG IN, set the dial for an upper frequency limit.
3.
For modulation with an ac input at VCG IN, center
the dial at the desired center frequency. Do not
exceed the maximum dynamic range of the selected
frequency range.
Figure 3-6 is a nomograph with examples of the frequency
dial effect as a reference for VCG IN voltages. Example 1
shows that with OV VCG input, frequency is as determined
by the main dial setting, 1.0 in this example. Example 2
shows that with a positive VCG input, output frequency is
increased. Examples shows that with a negative VCG input,
output frequency is decreased. (Note that the 50S2 OUT
Frequency Factor column value must be multiplied by a
frequency range multiplier to give the actual 50^2 OUT
frequency.)
3-3
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