Company Confidential
38
Raveon Technologies Corp.
2. Transmit random data on the center of the band, using the
ATTD 1
command. This command will cause the
M8T
to automatically key up,
and send random data for one minute.
3. Verify the DC center of the demodulated data is stable. The random data
should be randomly timed 1s and 0s, and have little to no AC component
on them. See pictures below for details.
4. If necessary, change the
ATR9
setting so that the long data bit have the
same amplitude and DC value as the shorter ones.
5. On the low end of the band, adjust
ATRL
so that the modulation is proper.
6. On the high end of the bamd, adjust
ATRH
so that the modulation is
proper.
11.6.
Carrier Detect
The Carrier Detect (CD) signal from the modem is output on pin 3. It may be
asserted by the 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.
Note: “Asserted” means low. “Negated” means high. The CD pin will sit at about
3.3V when CD is not asserted. A digital 1 (3.3V) on the CD pin is the standard
convention used to indicate no carrier detect. This allows the digital signals like
the CD pin to be connected to standard RS232 line driver circuits and operated
with the correct polarity.
Mode 0 - RF CD
On this line the modem indicates to the DTE that it has received a carrier from a
remote device. It will assert this signal any time there is a carrier detected. The
modem may be configured to assert this when an RF carrier is detected (any on-
channel RF, voice or data), assert it only when another RF modem signal is
detected, or always assert it. The operation of this line is configured with the
ATR1 command. The default is 1 (asserts when
M7
data is detected on the radio
receiver).
Mode 1 - Data CD
In this mode, the CD pin is asserted whenever the modem detect a valid data
modem signal on the air. If RF is present, but it is voice or some non-data single,
then the CD pin is negated.
Mode 2 - CD ON
In this mode, the CD pin is always asserted.
