Motorola BLE*/* - Manual (Page 23)

3-2 Amplifier Setup
BLE*/* Installation and Operation Manual
ƒ Perform a bench alignment. Pre-aligning the BLE*/* response on the bench (Section 4,
“Bench Testing”) for a system signature simplifies field alignment.
ƒ Field-sweep the entire bandwidth of the amplifier to correct frequency response for passive
signature and roll-off.
ƒ Close the housing in accordance with the instructions in Section 5, “Installation.”
Cable Equalizer
Select the appropriate model SFE-*-* to compensate for cable attenuation versus frequency and
to obtain the proper output tilt. The BLE*/* is equipped with the 8LDR/*/III interstage
equalizer and flatness board that compensates for cable attenuation. Any cable or passive slope
beyond that of the LDR must be compensated for by selecting and installing the appropriate
SFE-*-* cable equalizer.
Equalizers are available in 1 dB increments from 0 dB through 22 dB. The following examples
describe how to choose the correct equalizer.
Example 1
The amplifier location includes 20 dB of cable (at 870 MHz) between its input and the preceding
amplifier. Consider cable loss only. Exclude any flat loss due to splitters or other passive
devices. The internal equalizer, model 8LDR/8/III, compensates for approximately 8 dB of cable.
Subtract this cable length from the 20 dB of this example (20 – 8 = 12). The SFE-87-12 is the
proper equalizer in this case. With this equalizer installed, the BLE*/* reproduces the output
tilt of the last upstream amplifier.
When selecting an equalizer, choose the next lower value if the exact value is not available or in
cases where the calculated value makes two choices possible.
Example 2
The BLE87/* is used in a link following a fiber node with flat output. There is 16 dB of cable
between the node and the line extender, plus passive losses that are assumed to be flat. Which
is the proper equalizer to achieve the 10 dB of output tilt?
In this case, calculate the equalizer value by using the following method:
SLOPEeq = TILTout + SIGlo – SIGhi – SLOPEieq
where: SLOPEeq = required SFE-87 slope
TILTout = required amplifier output tilt
SIGlo = signal input level at channel 2
SIGhi = signal input level at 870 MHz
SLOPEieq = interstage equalizer slope (8 dB)
From various references, such as manufacturer’s catalogs, you can determine that 16 dB of cable
at the operating frequency of 870 MHz is 4 dB of loss at 54 MHz. This suggests that the channel
2 signal input level to the line extender is 12 dB greater (16 – 4 = 12) at channel 2 than it is at
870 MHz. Our example assumes that the high-end frequency level into the amplifier is
+15 dBmV.