6881094C28-D July 16, 2004
Radio Alignment Procedures: Front End Filter Alignment 6-11
6.9 Front End Filter Alignment
This alignment procedure adjusts the front end receiver bandpass filters for the best receiver
sensitivity and selectivity. This procedure should be performed for all test frequencies to allow for
proper software interpolation of frequencies between the test frequencies in the band
(see Figure 6-9 on page 6-12).
NOTE: Rx Front End Filter Alignment is required after replacing (or servicing) the transceiver board.
6.9.1 Procedure for VHF
Tuning is not necessary for the VHF band.
6.9.2 Procedure for UHF Range 1 and Range 2
Tuning is not necessary for the UHF Range 1 & 2 bands.
6.9.3 Procedure for 700 MHz Frequencies
To align the 700 MHz receiver front end:
1. Left-click the desired frequency field.
2. Apply an RF signal with no modulation at -90 dBm on the current operating frequency.
3. Start with a softpot value (approximately 10 or 20), increase softpot in ascending order, and
note the RSSI values. The RSSI will reach a peak value and remain stable and then
decrease. Allow the limits of the peak range to be defined as RSSI PEAK - 3. Choose the
middle of the peak range and program the corresponding softpot value as the tuned softpot
value.
4. Repeat the above process for all 700 MHz frequencies.
5. Click on the Program All button to save the tuned values in the radio.
6. Left-click the Close button on the screen to return to the Transmitter Alignments menu.
6.9.4 Procedure for 800 MHz Frequencies
To align the 800 MHz receiver front end:
1. Left-click the desired frequency field.
2. Apply an RF signal with no modulation at -90 dBm on the current operating frequency.
3. Start with a softpot value of 50, increase softpot in ascending order, and note the RSSI
values. The RSSI will reach a peak value and remain stable and then decrease. Allow the
limits of the peak range to be defined as RSSI PEAK - 3. Note the upper end of the peak
range and program the corresponding softpot value as the tuned softpot value.
4. Repeat the above process for all 800 MHz frequencies.
5. Click on the Program All button to save the tuned values in the radio.
6. Left-click the Close button on the screen to return to the Transmitter Alignments menu.
This procedure should only be attempted by qualified service technicians.
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