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SDA-5500/SDA-5510 Sweep Configuration: Sweep History and Theory

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channel. The only element that must be configured to match receiver and

transmitter prior to starting a sweep is the telemetry frequency.

Stealth Sweep

Early cable sweep systems worked by injecting sweep pulses at the points

to be measured. Unfortunately, the pulses generated by sweep transmitters

interfered with the video channels that customers were paying to watch.

The design of Acterna’s Stealth sweep system enables you to sweep

through most continuous carrier channels without injecting any signal. This

means there is absolutely no chance of interference. To accomplish this,

Stealth sweeping uses the channel carrier as the pulse that is measured. At

the designated time (when the channel plan dictates), the transmitter and

receiver both measure the appropriate carrier. In the telemetry channel, the

measured headend level is transmitted to the receiver. The difference

between the two simultaneous measurements is calculated, and thus the

frequency response of the system is measured without injecting sweep

pulses. It is important to note that this system can work only when a carrier

has a fairly stable power level. If the level changes too quickly and randomly,

the measurements in the headend might not match those in the field, and

sweep instability will result.

Reverse Sweep Theory

Sweeping the reverse path is different from sweeping the forward path. In

sweeping the forward path, the amplifier is aligned such that its output is

within set limits (the amplifier compensates for the cable closer to the

headend, before it in the distribution path). In sweeping the reverse path, the

amplifier still compensates for the cable closer to the headend, but this cable

is now after the amplifier in the distribution path. Thus, in sweeping the

reverse path, the amplifier is aligned such that the response at the headend

is within set limits from this amplifier alignment point. This is why it is

necessary to transmit the sweep from the amplifier test point and measure it

in the headend. This ensures that the system is correctly aligned to transmit

signals in the reverse path.

You align a return path system in much the same way as you do a forward

path system. The first point to be aligned is the optical node, or first

distribution amplifier. Sweep pulses are injected from the input to this amp,

then measured at the headend. The system is aligned so that the received

sweep pulses arrive with correct level and tilt. This first test point is now the

reference. Then each amplifier one level further away from the headend is

aligned in order, using the reference from the first test point. At each amp,

the system is aligned to match the response from the first test point as

closely as possible.

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Wavetek 147 Especificaciones Pagina 324