RF Neulink NL5000 Rev B0 - Manual (Page 13)

NL5000 User Manual Rev B0 12
5.4 OPERATING MODES
5.4.1 Digital/Data Mode
The primary mode of operation of the NL5000 modem is that of transmitting digital
data. Data received through the RS-232 pins on the I/O connector are combined
with error detecting and correcting bits along with bit synchronization and framing
pattern bits and converted into a 4-level pattern to be transmitted. The data stream
to be transmitted is also broken into blocks and then into packets or frames (a
collection of blocks) for easier error detection and correcting. The speed (baud
rate) of the stream is dependent upon the channel bandwidth and varies from 4800
bps (2400 baud) in a 6.25 kHz channel to 19.2 kbps (9600 baud) in a 25 kHz
channel. The actual data throughput is about half that of the over-the-air speed due
to the extra bits added as discussed above. At the receiving end, the 4-level data
stream is decoded and the information is passed to the host.
The length of the blocks is fixed, but the overall packet length can vary and
depends upon the timing of the reception of the data through the RS-232 pins.
The packets are formed as the length of the data stream reaches a certain
limit, determined by the modem itself or when a time gap in the reception of
the data occurs.
5.4.2 Voice/Analog Mode
In many situations it is desirable to be able to transmit voice or analog information.
This can be useful in determining whether an RF link has been established and in
troubleshooting situations. The NL5000 modem supports voice and analog input
signals in the 12.5 kHz and the 25 kHz versions; the 6.25 kHz version cannot
support voice due to its narrow bandwidth. The audio path gains on both the
transmitter and receiver are programmable via the Configuration Software. The
receiver has two audio outputs, one for line level operation and one which is able
to drive a speaker.
5.5
ANTENNA PLACEMENT
The NL5000 module is enclosed in a metal housing for RF shielding. However, RF
emitting sources located very close (less than 12 inches) to the unit can at times
affect its operation. It is not recommended that an antenna be connected directly to
the module’s BNC connector unless the RF output power is set for less than 1 watt
or the module is placed within another RF tight enclosure.
In addition, to ensure that persons are not exposed to RF levels above save limits,
observe the antenna to personnel distance limits in section 1.3.3.
5.6
ANALOG/VOICE INTERFACE