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Operation-SW 503
2 .2 .5 Sweep Rate Effects
When sweeping rf circuits having rapid amplitude
changes, errors may occur, due mainly todetectordelays .
Decreasing the detector output time constant will
minimize this effect . Figure 2-5 illustrates sweep rate
effect .
2-6
2.2 .6 Overloading Effects
2.2 .7 Low-Level Measurements
TRUE RESPONSE
RESPONSE WITH
SLIGHT ERROR
DUE TO SWEEP
RATE BEING
SLIGHTLY TOO
FAST
RESPONSE WITH
LARGE ERROR
DUE TO SWEEP
RATE BEING
FAR TOO FAST
Figure 2-5 . Errors from sweep rate effects.
To check for sweep rate effect, first set the sweep width
to its lowest practical amount, then increase sweep time
while closely observing the swept output response . Any
change in the response indicates the sweep rate is too fast
for a true response . When a further increase of sweep time
does not change the response, a true response has been
obtained .
The use of excessive input signals to the device under
test can cause overloading . To assure that this condition is
not present, and that the response is a true representation
of the device under test, turn the OUTPUT dBm
(ATTENUATION dB on SW 503 Option 1) and CAL
controls to minimize output amplitude . Gradually increase
the output amplitude until a response is obtained . Further
increase of the output amplitude should not change the
configuration of the response envelope except in
amplitude . If the response envelope does change, such as
flattening at the top, decrease the outputjust farenough to
restore the proper configuration.
When making measurements at low levels, the effects
of radiation and ground loops may become problems .
Using double-shielded cables for rf signals helps minimize
the radiation problem. Ground loops causing hum pickup
can sometimes be eliminated by completing only one
ground connection between each instrument . Thisapplies
particularly to the oscilloscope horizontal input. If the
ground connection is made at the vertical input terminal,
an additional ground at the horizontal input terminal will
often result in hum pickup .
2.2 .8 TV Receiver Interference
When using the SW 503 with a tv receiver, interference
from the receiver's horizontal sweep circuit may appear on
the response curve, making it difficult to observe a clearly-
defined trace . Therefore, we recommend that thetvsweep
circuit be disabled during testing .
2 .2 .9
Use With Digital Counter
The DOT POS control on the SW 503 functions only
when a digital counter with sweep interrupt logic, such as
the DC 502 Option 7, is used with the system . In use, the
SW 503 sweep generating voltage is interrupted at the dot
position (positionable with the DOT POS control), and the
counter is told to initiate a count. At the conclusion of the
counter gate time, the sweep is resumed . The counter
provides an accurate indication of the SW 503 frequency
at the dot location ; the dot is actually caused by the sweep
remaining stationary during the count.
In order forthe DC 502 Option 7 to work properly, both
An internal switch (S510) in the SW 503 facilitates
operation with X-Y plotters . This switch is located on the
marker selection assembly directly behind the RF OUT
connector (see Figure 2-6) .
zosi a
REFER TO TEXT,
SEC . 2 .2.10
Measurement sensitivity will be determined by the type
of detector used .
Figure 2-6 . Markers selection switch location .
units must be installed m specific compartments m a
TM 500-Series power module equipped with Option 7 .
This option adds the wires necessary to interface the two
units via their rear-panel connectors . See Subsection 5 .2
for further information (also see warning page preceding
Section 3) .
2 .2 .10 Operation With X-Y Plotters
For normal operation, the switch is set toward the front
panel . For plotter operation, with the switch set toward the
rear of the instrument, the high-frequency marker signals
are converted to a lower frequency (rectified) which is
compatible with the operating speed of the plotter pen or
styl us .
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