Field Sweeping with the SDA-5000: Loopback Sweep (OPT2)
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4
mode. Sweepless sweep must always be performed using references. After
several traces have been acquired, press the Function and 6 pqr keys to
store a reference. This will now be used as a sample of the ‘perfect’ system
levels against which other test points will be compared.
See Also
½ “Sweep References” in Chapter 11 has more information
about storing sweep references (page 201).
When you reach another test point, press Sweep again. If the desired
reference is not already in use, press the Function and 6 pqr keys to select
the appropriate reference. The sweep display will now show the level of
carriers at this point relative to the levels at the point where the reference
was stored.
It is important to remember that Sweepless sweep data is only as stable as
the carrier levels in your system. Because no transmitter is available to
cancel out headend drift, any change that happens in a channel level will
show up as a frequency response problem. For this reason it is very
important to use only stable channels as sweep points for sweepless sweep.
Also, you won’t see a frequency response where there are no carriers.
Loopback sweep is a new feature of the SDA-5000 with OPT2 (transmit).
With Loopback testing, you can perform a rough frequency response, gain,
and loss test on active and passive devices in the field. It can be used for
amplifier pre-alignment and for testing amplifiers in isolation from the rest of
the system. It is also useful for testing the integrity of a cable before it is
installed.
You set the sweep insertion level and create the loopback sweep plan from
the main SWEEP configuration menu after selecting Loopback as the sweep
mode.
After connecting to the test point, use the up and down diamond keys to
select Loopback from the main SWEEP menu.
The Loopback SWEEP screen shown in Fig. 4-23 is displayed when you
press the Sweep measurement mode key after you have selected Loopback
from the main SWEEP menu.
LOOPBACK SWEEP (OPT2)
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