User Manual

DE
DANIELS
ELECTRONICS
VT-4R150 VHF Project 25 Digital Transmitter Instruction Manual 3-3
measured by the frequency counter matches the test frequency displayed on the screen to within
+/- 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
Transceiver RF Board disconnected from the amplifier module and continue with the next
alignment procedure.
3.4.4 Transmitter Deviation Balance Adjustment
This adjustment equalizes the modulation sensitivity of the low and high frequency modulation
paths on the Transceiver RF board. To perform the adjustment, disconnect the Transceiver RF
Board from the amplifier module by separating the SMB connectors. Connect the RF output cable
of the Transceiver 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. Se lect 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 d eviation 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 within +/- 2%. When
the deviations match, clic k on the "UPDATE SOFTPOT" button to save the setting in the
transmitter's non-volatile memory. Repeat the adjustment process for each of the test frequencies.
Leave the Transceiver RF Board disconnected from the amplifier module and continue with the
next alignment procedure.
3.4.5 Transmitter Deviation Limit Adjustment
This adjustment prevents over deviation of the transmitter's carrier. To perform the adjustment,
disconnect the Transceiver RF Board from the amplifier module by separating the SMB
connectors. Connect the RF output cable of the Transceiver 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 Digital Signal Processor Board.
3.4.6 Audio Level Alignment
The audio level should be set after all other alignments have been completed. The transmitter
should be programmed to an analog channel for the purposes of the test, since the vocoder in the
transmitter encodes pure sine signals with a large amount of distortion. The transmitter ’s
Unbalanced Audio input (at P1-Z18) should be connected to an audio signal generator set up to
deliver a 1 kHz tone at a level of 308 mVRMS (-8 dBm in a 600 ohm system). The RF output of