User Manual

ADCP-75-179 • Preliminary Issue A • September 2004 • Section 3: Operation

Page 3-8

2.3 Determine Forward Path Input Signal Level

The level of the composite RF input signals received at the host unit 851–869 FORWARD RF

IN and 935–940 FORWARD RF IN ports will vary depending on the EBTS, the cable loss, the

number of channels present, and the required forward path composite power. If maximum

composite RF output is required at the RU, the level of the composite RF input signal received

at the HU must fall within a range of –12 to –43 dBm. If the signal level is not within this range,

it must be adjusted using an external attenuator.

When connecting a single HU to a single EBTS, use the following procedure to measure and

adjust the input RF signal level at the HU:

1. Connect a spectrum analyzer or power meter to the 851–869 MHz forward path output

port at the EBTS. The required signal levels and test points are shown in Figure 3-5.

2. If using a spectrum analyzer, proceed to step 3. If using a power meter, measure the

composite signal power from the EBTS 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 EBTS using the following formula:

tot

= P

+ 10Log N where,

tot

is the total composite power in dBm

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 EBTS 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:

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.

Note: Check the input rating of the test equipment and the output rating of the EBTS. To

avoid burning out the spectrum analyzer or power meter, it may be necessary to insert a

30 dB 100W (or similar) attenuator between the EBTS and test equipment.

Note: If the input signal level is already within the required range of –12 to –43 dBm, then

no external attenuator is required.