RF Neulink NL5000 Rev B0 - Manual (Page 14)

NL5000 User Manual Rev B0 13
5.6.1 Transmitter
The analog/voice input for the modem is on pin 1 (AUDIO IN) of the 15-pin I/O
connector. Signals at this input are modulation limited and filtered before being
presented to the modulator. Via the Configuration Software, the gain of this signal
path can be adjusted and pre-emphasis or a flat audio response can also be
selected. Transmitting a signal from this input normally requires that the pin 12
(TEST) of the I/O connector be taken to the active state. The active state can be
set via the Configuration Software and is normally set for active low logic level.
Note that the TEST pin can be set via the Configuration Software to send other
types of signals such as digital test patterns and must be set via the Configuration
Software to activate the analog/voice channel and transmit the analog/voice signal
when asserted.
5.6.2 Receiver
The receiver has two audio outputs, a line level output and an output which can
drive a speaker load. There are a number of parameters which can be set via the
Configuration Software for these two outputs. The line level output on pin 2
(AUDIO OUT) of the 15-pin I/O connector can be selected to have either a flat or
de-emphasized audio response and its level can be adjusted. Pin 3 (SPEAKER) of
the 15-pin I/O connector is the output of the audio PA and is capable of driving 8-
ohm speaker loads. This output is always de-emphasized and its level is set via
the Configuration Software with the same adjustment as the AUDIO OUT signal.
Note that the AUDIO OUT and SPEAKER levels cannot be set independently since
they share the same adjustment.
In order for audio to be present at either of these outputs, the received signal RF
level must be above the carrier detect level set via the Configuration Software.
Both the carrier detect on and carrier detect off levels can be set and are the same
as the levels used by the data modem when the modem is set to use carrier detect
for the detection of a packet (see below).
5.7
DATA STREAM PACKET DETECTION MODES
In order for the receive modem to properly synchronize to a transmitted packet of
data, the packet data blocks are preceded by a bit synchronizing block and a frame
synchronizing block. The receive modem looks for the bit synchronizing pattern to
determine that a packet of data is forthcoming. The modem can be programmed to
do this continuously on the raw discriminator output or only when a signal has
been detected on the basis of the carrier detect circuitry.
There is a tradeoff in choosing between these two modes. If the radio’s carrier
detect circuitry is not used, the modem must continuously sample the noise and