Company Confidential
23
Raveon Technologies Corp.
3. Adjust the deviation register setting so that the frequency is exactly
2.0kHz low. The deviation is set with a digital adjustment. Use the
ATR0 command to read or set the value. This value is negative, and is
typically around -200.
TX Modulation Balance
1. Transmit an alternating 10101.. pattern using the ATTD 8 command.
2. While monitoring the modulation using an FM demodulator, adjust the
balance digital pot value, by setting it with the ATR9 xx command. xx
= 0 - 127, and is typically around 40 for good modulation and a
deviation of 2.0kHz.
3. Transmit random data, using the ATDT 1 command. Verify the DC
center of the demodulated data is stable.
4. If necessary, change the ATR9 setting so that the long data bit have
the same amplitude and DC value as the shorter ones.
RX DC Offset Verification
To verify that the DC center of the received signal is near the nominal value,
perform the following steps:
1. Generate a test signal, 1kHz tone, 1.5kHz deviation, on the receive
frequency. Connect the signal generator to the antenna input. Set the RF
level to -90dBm.
2. Measure the average voltage at TPRX1 on the modem circuit board.
3. The DC voltage should be between 1.0 and 2.0 volts, and the p-p voltage
of the sine wave should be greater than 50mV and less than 2 volts.
RX Carrier Detect
The DCD signal from the modem may be generated by detection of RF, using
an internal signal called RSSI (Receive Signal Strength Indication). The RSSI
signal is an analog signal representing the strength of the RF carrier. It is
compared with a pre-set value, and if it is above this value, Carrier Detect is
asserted. The pre-set value may be change with the
ATRA
command. To
set it, perform the following steps:
1. Generate a test signal, 1kHz tone, 1.5kHz deviation, on the receive
frequency. Connect the signal generator to the antenna input. Turn the
RF level off.
2. Watch the RSSI value by issuing the
AT$5
command. The current
reading will be sent out the serial port.
3. Adjust the RF level to a point where you would like the RSSI to trigger the
CD signal. This is factory-set to -115dBm.
