Sweep Out; External Sweep; Amplitude Modulation - TTI TG550 Manual De Instrucciones

Sweep Rate
The generator sweeps both up and down at the speed set by the RATE control, i.e. it does not
reset rapidly after the upward sweep. This has the advantage that the suitability of the selected
sweep time can be continuously monitored.

Sweep Out

When INT SWEEP is selected the SWEEP IN/OUT socket becomes an output providing a 0V to
3V ramp from 600Ω impedance to drive the X-input of an oscilloscope or chart recorder.
Terminating this output with a resistor will reduce the output amplitude. Terminating with 600Ω will
halve the output giving 0V to 3V.
Holding in the SET STOP button holds the ramp at the maximum and can therefore be used to
set full scale on the oscilloscope or chart recorder.
Note that when SWEEP IN/OUT is used as an output to drive the X-input of an oscilloscope, the
oscilloscope should be set to DC coupling and not AC coupling which will cause a double image
at slow sweep speeds.

External Sweep

When EXT SWEEP is selected the SWEEP IN/OUT socket becomes an input. The generator
frequency can be swept, DC programmed or modulated by a suitable control voltage applied to
this input. The instrument sums the SWEEP IN voltage with the internal control voltage derived
from the FREQUENCY vernier to determine the operating frequency; the display shows the
resultant frequency.
A positive voltage increases the frequency; for frequency control with positive-going DC inputs the
vernier should therefore be set to the lower frequency limit of the range to be swept. For example,
a 0V to +3V signal will sweep the generator 3 decades up from range minimum, set by the
vernier, to range maximum.
Similarly, a negative voltage decreases the frequency and for negative-going DC inputs the
vernier should be set to the upper frequency limit of the range to be swept. For example, a 0V to -
3V signal will sweep the generator 3 decades down from range maximum, set by the vernier, to
range minimum.
To use a sweep signal which is symmetrical about ground, the vernier should be set to give a
frequency at approximately the centre of the band to be swept.
In external sweep mode the LIN/LOG selection is inoperative, i.e. the FREQUENCY vernier is
always operating linearly, as marked.
Note: Non-linear operation may result when the sweep input voltage is excessive; that is, when
the attempted generator frequency exceeds the range limits.

Amplitude Modulation

Depressing the AM ON/OFF button selects AM. The depth of modulation can be adjusted over a
0% to 100% range using the modulation DEPTH control. When AM is selected the output
amplitude will drop to 50% at 0% modulation.
With the AM INT/EXT button in the INT (internal) position, the modulation source is an internal
400Hz sinewave oscillator. The INT-AM annunciator is displayed.
With the AM INT/EXT button in the EXT (external) position, and the EXT COUNT/EXT AM button
in the EXT AM position, external AM modulation is possible via the AM/COUNT IN socket; the
AM-EXT annunciator is displayed. The modulating signal applied should have no DC offset or
should be AC coupled. A 2V peak-to-peak signal gives approximately 100% modulation with the
modulation control at maximum. Modulating the generator with a squarewave gives step changes
in the output amplitude which are suitable for testing signal compressors and automatic gain
controlled circuits.
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