Synthesised Radio Modem
Key Transmitter
X8200
X8200HP
The Key Transmitter setting switches on the transmitter so that a radio site survey can be
conducted. . A second Radio Modem can be used to move around the site observing either
the Rx LED or the RSSI Bar Graph. If the Rx LED is on or there are more than 3 bars on the
RSSI Bar Graph then there will be good communications.
RSSI Relative Signal Strength Indicator
The RSSI function is used to detect radio activity on the RF Channel. It can also be used to
measure the signal strength of a transmission from a distant radio modem.
A maximum of nine bars will appear relating to a signal strength of 0.3uV (-112dBm) to
In the Remote Access Mode the distant modem will measure its own RSSI and radio the value
back to the local radio modem were it will be displayed on a bar graph in the menu.
Comms Speed
Two over air transmissions speeds can be selected. These are:
F = 10Kbits/sec
S = 5Kbits/sec
Address Mode
The address mode uses ID numbers to “dial up” distant modems. When the data is transmitted
from a distant modem the first ID number set in the repeater path is added to the data string
and used as a transmitter address. The receiving modem compares the transmitter ID in the
data string with its own ID number. If they are the same the data string is passed to the serial
port. In addition individual modems can be dialled up by using serial ATT and ATA Instructions
to change the transmitting ID number.
The ATT instruction can be used to
“
dial up” distant modems as shown in fig 4. The base
station modern has its ID number (receiver address RXA) set to 01. The four distant stations
have ID numbers 2,3,4 and 5. All of the distant modems have the first value in their Repeater
Path (transmitter address TXA) set to 01. Therefore any distant modem can transmit data to
the base station but not to each other.
The serial ATT instruction is made up of the ASCII characters for A (41), T(54), T(54). This is
then followed by the ID number of the addressed station as two ASCII numbers 30 to 39
The instruction sent by the base station to address modem with ID set to 2 will be:
A
41
T
54
T
41
0
30
2
32
DATA
Modem 3 can be dialled up in the same way with the instruction:
A
41
T
54
T
41
0
30
3
33
DATA
The instruction string will not be transmitted over the air as long as it is sent to the modem
without any breaks.
DS8200-2 April ’07
©2007 RF Solutions Ltd, www.rfsolutions.co.uk
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