User Manual

ADCP-75-158 • Preliminary Issue A • June 2003 • Section 4: Operation
Page 4-8
© 2003, ADC Telecommunications, Inc.
2. If using a spectrum analyzer, proceed to step 3. If using a power meter, measure the
composite signal power from the BTS and then proceed to step 5.
3. Measure the RF level of a single carrier, such as the control channel, in dBm. Make sure
the resolution bandwidth of the spectrum analyzer is 30 kHz. Maximum power in any
channel should not exceed 5W (+37 dB).
4. Calculate the total composite signal power from the BTS using the following formula:
P
tot
= P
c
+ 10Log N – (see Note)
Where,
P
tot
is the total composite power in dBm
P
c
is the power per carrier in dBm as measured in step 3, and
N is the total number of channels.
5. Determine the total cable loss that is imposed by the forward path coaxial cable that links
the BTS to the HU and also any insertion loss imposed by splitters or combiners.
6. Subtract the total cable loss and any insertion losses from the total composite power
calculated in step 4.
7. Subtract –25 (midpoint of the required range) from the value determined in step 6. The
difference (which should be positive) equals the value of the external attenuator that is
required to reduce the forward path signal level to fall within the required range. The
following formula outlines the required calculations for steps 6 and 7:
P
tot
– (Cable and insertion loss) – (–25) = Value of external attenuator required
8. Select an attenuator that is as close to the value calculated in step 7 as possible. Select a
value that will adjust the signal level of the composite input signal to fall within the
specified range.
9. Install the external attenuator in the coaxial cable that is connected to the FORWARD RF
IN port at the HU.
10. Subtract the value of the external attenuator used in step 9 from the total composite signal
power (P
tot
) and record the result. This value will be required when setting the attenuation
of the HU’s internal forward attenuator.
Note: If calculating the composite power for a CDMA system, reduce the initial result by
16.23 dBm
Note: If the input signal level is already within the required range of –9 to –40 dBm, then
no external attenuator is required.
Caution: The Host Unit can be damaged if it is overdriven by the BTS. Always install an
external protective attenuator at the Host Unit FORWARD RF IN port if the forward path
composite input signal level is greater than –9 dBm.