Example 1; Example 2 - Motorola BLE Series Installation And Operation Manual

3 3 3 3 - - - - 2 2 2 2 A m p l i f i e r S e t u p
that of the LDR must be compensated for by selecting and installing the appropriate SFE-*-*
cable equalizer.
Equalizers are available in 1 dB steps from 0 dB through 22 dB. The following examples
describe how to choose the correct equalizer.
E xa m p le 1
The BLE75/* is used in a cascade of amplifiers which operate with 10 dB of cable. System
records show that 20 dB of cable exists between the line extender and the previous unit.
To obtain the correct equalizer value, subtract 10 dB, the 7LDR/7/II equalizer value, from 20
and the result is the required equalizer (20 − 10 = 10). Therefore, the correct equalizer is a
model SFE-75-10. When selecting an equalizer, choose the next lower value if the exact value is
not available.
Install the proper cable equalizer. To obtain the required output tilt the minimum attenuation
of the cable connected to the input is 10 dB (7 dB slope at 750 MHz).
E xa m p le 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 which 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:
SLOPE eq = TILT out + SIG lo – SIG hi – SLOPE ieq
where: SLOPE eq = required SFE-87 slope
TILT out
SIG lo
SIG hi
SLOPE ieq = 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.
Substituting this information in equation (1) provides the following result:
10.0 dB + 27 dB – 15.0 dB – 8.0 dB = 14 dB
The slope of the required equalizer is 14 dB. Table 3-1 and Figure 3-1 show that 14 dB of slope
is caused by approximately 18 dB of cable at 870 MHz. Therefore the correct equalizer is model
SFE-87-18.
B L E * / * I n s t a l l a t i o n a n d O p e r a t i o n M a n u a l
= required amplifier output tilt
= signal input level at channel 2
= signal input level at 870 MHz