Wavetek 147 Spécifications télécharger pdf (Page 347)

Application Notes: Reverse Sweep and Balance

323

into account extra accessory losses such as internal

"feedermakers" and input pads if warranted. The reasoning

behind constant inputs to the port vs. hybrid is beyond the

scope of this application note.

The reference line on the display should also be X dB. Look at M1 and M2

on the Stealth field unit display to verify. The "Ref" on the sweep display is

the middle graticule line, not the actual sweep level.

NOTE: The sweep trace displayed on the field unit will

change if someone in the headend changes the test point

compensation on the Tx. This also affects the Reverse

Alignment mode on the field unit.

Others may use test point compensation and change the injected telemetry

level to account for different test points, different recommended injection

levels, and extra accessories. They then balance to a 0 dB reference line

and the same telemetry reading as was achieved at the reference.

NOTE: The SDA unit works a little differently. The reverse

test probe value adds to the telemetry and sweep values to

give the actual output of the field unit. It also has a Reverse

Alignment mode, which can only be accessed through the

Navigator mode. The markers give actual received levels in

the Headend as if using 2 CW carriers with a "Raw" sweep

behind it.

Another Way

Suppose you have a node with 20 dB test points and a recommended in of

15 dBmV, and a trunk amp with 25 dB TPs and recommended in of 17

dBmV. The Bridger amp with 25 dB TPs has a recommended in of 15

because you are balancing constant inputs of 10 dBmV to the hybrid, and

the internal loss from the test point to the hybrid is 5 dB vs. 7 dB for the trunk

amp. There is also an LE with a 26 dB tap for injection and a recommended

in of 12 dBmV.

After adding all the numbers and the extra loss of 3.5 dB from the

summation network (splitter) used in reverse balancing, the total generator

output would be:

Node = 20+15+3.5=38.5, Trunk = 25+17+3.5=45.5,

Bridger = 25+15+3.5=43.5, LE = 26+12+3.5=41.5

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Wavetek 147 Spécifications Page 347