DE
DANIELS
ELECTRONICS
UT-4B400 P25 Digital UHF Base Transmitter Instruction Manual
2-7
2.5.1.1
Reference Oscillator Adjustment
The reference oscillator provides an accurate frequency standard to which the transmitter's carrier
signal is phase locked. To adjust the reference oscillator frequency, disconnect the RF Board from
the amplifier module by separating the SMB connectors. For this test, the RF board will generate
a 0 dBm RF signal from its RF output. Connect the RF output cable of the RF board to a
frequency counter or communications test set. Connect the transmitter to an IBM compatible
computer using the Programming Cable. Apply power to the transmitter and run the Radio
Programming Software. Navigate to the TRANSMITTER \ SERVICE \ REFERENCE
OSCILLATOR menu, where you will see a test frequency displayed and a slider to adjust the
frequency. Click on the "ENABLE TX" button and move the slider until the frequency measured
by the frequency counter matches the test frequency displayed on the screen to /- 150 Hz.
Click on the "UPDATE SOFTPOT" button to save the setting in the transmitter's non-volatile
memory. This completes the adjustment of the reference oscillator. Leave the RF Board
disconnected from the amplifier module and continue with the next alignment procedure.
2.5.1.2
Transmitter Deviation Balance Adjustment
This adjustment equalizes the modulation sensitivity of the low and high frequency modulation
paths on the RF board. To perform the adjustment, disconnect the RF Board from the amplifier
module by separating the SMB connectors. Connect the RF output cable of the RF board to a
communications test set. Connect the transmitter to an IBM compatible computer using the
Programming Cable. Apply power to the transmitter and run the Radio Programming Software.
Navigate to the TRANSMITTER \ SERVICE TRANSMITTER \ DEVIATION BALANCE screen,
where you will see a list of test frequencies and current SoftPot values for each frequency.
YSelect the radio button next to the first test frequency and click on the "LOW PTT" button. This
causes an internally generated 80 Hz tone to be applied to the modulator. Note the deviation of the
carrier on the communications test set, and click on the "HIGH PTT" button. This causes a 3 kHz
tone to be applied to the modulator. Adjust the slider next to the test frequency until the measured
deviation matches that of the 80 Hz tone. Now click on the "LOW PTT" button again to check the
deviation. If the deviation has changed from the original reading, note the new deviation and
perform the adjustment at the high frequency again. It may require several iterations of this
process to get the deviations to match /- 2%. When the deviations match, click on the
"UPDATE SOFTPOT" button to save the setting in the transmitter's non-volatile memory.
YRepeat the adjustment process for each of the test frequencies. Leave the RF Board disconnected
from the amplifier module and continue with the next alignment procedure.
2.5.1.3
Transmitter Deviation Limit Adjustment
This adjustment prevents over-deviation of the transmitter's carrier. To perform the adjustment,
disconnect the RF Board from the amplifier module by separating the SMB connectors. Connect
the RF output cable of the RF board to a communications test set. Connect the transmitter to an
IBM compatible computer using the Programming Cable. Apply power to the transmitter and run
the Radio Programming Software. Navigate to the TRANSMITTER \ SERVICE
TRANSMITTER \ ADJUST DEVIATION LIMITS menu item, where you will see a list of test
frequencies and current SoftPot values for each frequency. Select the radio button next to the first
test frequency and click on the "ENABLE TX" button to key the transmitter. Adjust the slider next
to the selected test frequency under the measured deviation of the carrier is between 2785 Hz and
2885 Hz. Click on the "UPDATE SOFTPOT" button to save the new setting to the radio's non-
volatile memory. Repeat the process for each test frequency. This completes the adjustment
process for the transmitter deviation limits, and completes the alignment process for the Main
Board.
