Sweep Function - Deviser DS2831 User Manual

Part II: Settings and Measurements
13-1.1 Settings
The following parameters can be adjusted in the USG mode.
Freq. range: 5~120MHz. This range allows network characterization over 42 MHz [NA] or 65 MHz [EU],
as diplex filter field upgrades continue.
Standard: J.83A, J.83B
Symbol Rate: 1.00 ~ 7.00MS/s
Level: 0 ~ 60dBmV
Modulation: Annex A: CW, QPSK, 16 / 64 / 256 QAM
Annex B: CW, 64 / 256 QAM
SHIFT: -6dB~+6dB (used to compensate for the test cable length or input port insertion loss)
13-2

Sweep Function

The USG application offers a frequency stepping (sweeping) function. Follow the instructions below to
activate it.
Press Sweep> (F2) to open the frequency sweep submenu. Here, press Freq (F3)to open a dialog for setting
the start/stop frequencies of the sweep. You can set up to 4 guardband frequencies.
The shadowed parts on the display screen will show the currently programmed guardbands. For a CW
signal sweep, the frequency steps are 1MHz, and the sweep will only jump over guardband frequencies. For
modulated signals, since the bandwidth occupied by the signal is large, the guardbands are equal to half
of the generated test signals, directly related to the symbol rate of the test signals selected. This may limit
the symbol rate required, depending on spacing available between live (desired) signals.
Even if the instrument has started transmitting test signals, amplitude adjustments can be made by pressing
the [+1dB] and [-1dB] function keys to ensure that the amplitude of the transmitted test signals is exactly as
desired. The frequency and amplitude of the sweep test signals will dynamically update on the screen. This
helps to prevent measurement errors; unlike levels, frequency cannot be adjusted during a measurement.
The Interval key allows the user to set a delay between each of the test carrier frequency steps to be
generated, speeding up or slowing down the sweep motion. This delay may range from 100~1000ms.
Single/Repeat, meanwhile, is used to control the frequency sweep to run a single cycle or on a running
loop until you press the Stop key.
By default, the DS2831's RF port is used for test signal output. Press RF/COM (F4) to toggle the output port to
COM instead.
As a general safe practice, always initiate a USG test signal transmission with levels as low as possible at first
and work your way up to a level quasi-equal to that of your live DOCSIS signals. This prevents introducing
unnecessary additional RF power, potentially overdriving your lasers, and introducing non-linear distortions
on your network.
Finally, press Zero (F7) to self-calibrate the USG. The cable connection of self calibration is shown as Figure
19 2 to connect RF port and COM port. At this moment, COM is USG output port, the output signals will
enter RF port and are received by DS2831 itself spectrum function, then execute self calibration and
generate the compensation data. If user select
calibration and generate the compensation, but if user select
the compensation data but use signal generator itself original calibration data.
106
C AL ON , the application will execute self
【 有 效 】
CAL OFF
【 无 效
, signals emission will not use
】