11) Adju
st the “IF Trim” for equal amplitude of the noise on the top and bottom of the demodulated and band pass limited
square wave as shown in the photo below. This adjusts the 43.2 MHz 2nd local oscillator frequency to center the
signal in the 450 kHz pass band. The DC discriminator output level will also vary as this is adjusted. The adjacent
channel rejection is also affected by this tuning.
Squelch
12) Although squelch levels are not used in NXDN communications the carrier detect amber LED can be set to serve as a
diagnostic of channel activity. Recall that the amber LED will flash when RSSI detection level is exceeded and be a
solid color when and if an NXDN signal is detected.
13) Clic
k the “Alignment” tab then “CD Calibration” and follow the instructions on that tab. Here you will calibrate at two
predefined RF levels and once done set the squelch on and off levels in the two other boxes. This is done by typing in
your desired “Carrier Detect ON” and “Carrier Detect OFF” levels in the boxes. The yellow RX LED will blink when a
carrier is detected in this range.
TRANSMITTER
1) Verify the TX Duplexer Input Port is connected to the TX RF port J201 of the PCB.
TX Frequency Adjustment
NOTE: After each adjustment, click on the “Program Repeater” button then the “Read Repeater” button to save
and read the radio information.
2)
Click the “Alignment” tab, the “Frequency/Power” button, and then click “Center Frequency on Repeater Frequency”
button
. By clicking the “Transmit” button at the top of the form you can now adjust the TX Frequency of the Repeater
to /- 50 Hz. Click
the “Transmit” button to stop transmitting.
TX VCO Band, Modulation Balance and Deviation Adjustment
3) a.
Click the “Alignment” tab and then the “Deviation/Balance” button. Now select “Auto alignment- Upper Edge
Balance”. Click the “Transmit” button. Transmit Frequency is 470 MHz, the VCO tuning voltage at TP201 should
measure 4.0 +/- 0.2 Vdc, if not, adjust C296.