Service Manual

61
Rated Volume Tuning Under Rx Align, select Rated Volume.
NOTE: The received audio output is taken from the positive
terminal of C189.
1. Inject a -47 dBm RF Signal modulated with 1 kHz tone at the 60%
rated deviation (see Table 10) into the VRS750.
2. Adjust the softpot value by using the slider, keying in the edit box
(press ENTER to confirm selection/send a softpot value), or via
the spin controls. Repeat this until a 1.58 Vrms ±200 mVrms
signal can be obtained at the positive terminal of C189.
3. Press Program to commit the softpot value into the codeplug.
Reference Oscillator
Warp
NOTE: Perform this operation prior to all other transmit
tuning operations in order to minimize heating and
because of the impact of warp on signaling operations.
1. Under Tx Align menu, select Reference Oscillator Warp.
2. There is only 1 frequency point shown which is always the last
non 0 transmit frequency point, which will normally be F7.
3. Click on the slider thumb. Press PTT Toggle to key up the radio at
the corresponding frequency point.
4. Monitor the transmit frequency.
5. Adjust the slider, spin or edit control (press ENTER to confirm
selection/send a softpot value) until the frequency is as close as
possible to the indicated transmit frequency (refer to Table 11).
6. Dekey the radio by pressing PTT Toggle.
Table 10. VRS750 Deviation Levels
Channel Spacing
(kHz)
Rated System
Deviation (kHz)
Signal Generator
Deviation (kHz)
12.5 2.5 1.5
20 4.0 2.4
20 5.0 3.0
25 5.0 3.0
30 5.0 3.0
Table 11. Frequency Error Specifications
RF Band Target (Hz)
VHF (136-174) ±200
UHF Band 1 (403-470) ±200
UHF Band 2 (450-527) ±200