Service Manual

60
Under Rx Align, select the Front End Filter option.
1. Inject a -70 dBm RF Signal with Frequency F1 (for UHF)/F3 (for
VHF) modulated with 1 kHz tone at 60% rated deviation (see
Table 10) into the VRS750. A 1 kHz tone must be detected at the
RX Audio connector on the test box to verify that the radio is
receiving.
2. Measure the RSSI voltage with a DC voltmeter capable of 1 mV
resolution at test point 111 on the VRS750. It is recommended
that an RCA filter (1.5 K-47 uF) be added at the input of the
voltmeter to reduce RSSI noise.
3. Increment the softpot value by adjusting the slider, keying in the
softpot values in the edit box (press ENTER to confirm selection)
or using the spin control until the maximum RSSI voltage has
been achieved.
4. For UHF and VHF radios:
a. UHF radios: Choose the next frequency and repeat steps 1 to
3 until all seven tuning points are done.
b. VHF radios: Calculate the softpot offset by subtracting the
default softpot value for F3 from the tuned softpot value for
F3. Add the calculated offset to all default values and enter the
results in the edit boxes for the appropriate softpot
frequencies.
5. Press Program to commit the softpot values into the codeplug.
Table 9. Default Softpot Values for VHF and UHF
Frequency Point
Softpot Value (Decimal)
VHF UHF
F1 36 38
F2 57 48
F3 84 79
F4 124 110
F5 166 135
F6 195 161
F7 225 186