5-9
mine the desired input level. For the sweep to arrive at the active
device input 10 dB below the level of other services in the reverse
spectrum, subtract 10 dB. Next, add the passive losses within the
amplifier, including any internal splitting, the reverse sweep inser-
tion test point loss, and/or any probe loss. The result gives the proper
output level setting for the 3SR. For example, let us say that the
return manufacturer specifies an input level of 20 dBmV (assuming 4
analog video channels). Subtract 10 dB to get 10 dBmV for the sweep
input level to the amplifier. The path loss from the Model 3SR to the
input of the return amplifier equals - 3.5 (splitter to enable transmis-
sion of reverse sweep and reception of forward telemetry) -30 (test
point) -1.5 (diplex filter) -3.5 (internal coupler for bridged ports. This
gives 10 dBmV + 3.5 dB + 30 dB + 1.5 dB + 3.5 dB for a sum of 48.5
dBmV for reverse sweep output level.
An alternative method for determining the optimum reverse sweep
output level is to observe the reverse spectrum at the headend
reverse sweep receiver (Model 3ST or 3HRV). The spectrum should
be 'max held' for an extended period (one half hour or more), then
printed or uploaded to a PC using StealthWareTM. This will identify
the active digital service frequencies and their level as they arrive at
the headend reverse sweep receiver. Next, a CW signal at an unoccu-
pied frequency is injected at the node sweep insertion point. The
level is adjusted and monitored by the technician in the headend
until it is 10 dB lower than the digital services as displayed on the
'max held' spectrum. The attenuator setting is subtracted from
+50 dBmV to obtain the proper reverse output level.
5.2.2 Generating a CW Test Signal
The 3SR may be configured to generate a CW signal for diagnostic
purposes. Proceed as follows:
NOTE
NOTE
NOTE
NOTE
NOTE: The unit must be in General setup mode.
The unit must be in General setup mode.
The unit must be in General setup mode.
The unit must be in General setup mode.
The unit must be in General setup mode.
1.
Cursor down to Diagnostics.
2.
Press Enter and cursor down to Transmitter Diagnostics.
Summary of Contents for 3SR
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