Service Manual

8. Press Toggle Bias 1 in order to enable the PA Bias softpot.

9. Increase the softpot value to obtain Z until Z-Y is within the

range for Bias Current as indicated in Table 13.

10. Press Toggle Bias 1 again to disable the PA Bias softpot.

11. Program the Bias softpot into the radio’s codeplug via pressing

Program.

12. Exit the PA Bias High Power function.

13. Under Tx Align, select PA Bias, Low Power. (If UHF, skip to step

15 and continue to Procedure 2.)

14. Repeat steps 3-11.

15. Exit the PA Bias Low Power function.

PA Bias Tuning for UHF

Low Power VRS750s

(Procedure 2)

NOTE: Failure in the instructions below means that you

cannot get a reading which is within the range of the

current window as speciﬁed in Table 14 for each

individual step.

Ensure that the radio’s antenna output is terminated to a 50 Ohm

load. This is to prevent self destruction of the PA.

STEP 1 1. Under Tx Align, select PA Bias, select Low Power.

2. Measure/read the dc current drawn from radio (speciﬁcations will

vary from radio to radio). Call this X. This value should typically

range from 70-100 mA or 0.07-0.1 A.

3. Press Toggle Voltage to enable the PA control voltage edit box/

spin control.

4. Increase the Voltage softpot value and measure/read from current

meter. Call the new value Y.

5. Increase Y until Y-X is within the range given for PA current in

Table 14 (STEP 1) below.

****** If a failure occurs, go to STEP 2 otherwise proceed

6. Press Toggle Voltage again to disable the PA control voltage edit

box/spin control.

7. Press Toggle Bias in order to enable the PA Bias softpot.

8. Increase the softpot value to obtain Z until Z-Y is within the

range for Bias Current as indicated in Table 14 (STEP 1).

Table 13. PA Bias High Power Speciﬁcations UHF/VHF VRS750s

RF Band PA Current (mA) Bias Current (mA)

VHF 90-110 90-110

UHF Band 1 30-45 600-700

UHF Band 2 30-55 400-480