RF Neulink NL5000-T - Manual (Page 15)

15
5.4 OPERATING MODES
5.4.1
RECEIVE
Carrier Detect and Squelch Operation
The NL5000-T is a transceiver; i.e. it can receive and transmit, although not at the same time. A
carrier detect system exists within the unit to detect the presence of a carrier which controls the
logic state of the DCD (data carrier detect) output. The RF levels at which this output changes
state are programmable. In addition, the unit may be programmed such that the audio outputs,
AUDIO OUT and AUX OUT, are muted (squelched) in conjunction with DCD operation. In units
where squelch operation has been enabled, the RX MON input can be used to override a squelched
condition. The DCD output is not affected by the RX MON operation.
Receiver Audio Outputs
Two receiver audio outputs are present on the NL5000-T module. The AUX OUT is general
purpose output which can have pre-emphasis enabled or bypassed. Its gain can be controlled and
its output is designed to drive 600 Ω loads. The coupling from the discriminator on the RF board
may be set to AC or DC by the programmer. The output stage is AC coupled, but can be modified
for DC coupling. See the maintenance section of the manual for details on this modification. The
AUDIO OUT is always de-emphasized, but its gain can be programmed. In addition, transmit
sidetone can be programmed as an option, if desired. This output can drive 8 Ω speaker-type
loads.
5.4.2
TRANSMIT
PTT Operation
The transmitter is activated by placing the PTT/RTS (Push-To-Talk/Request-To-Send) input in its
true state. This state is programmable. If the unit is to operate in simplex (transmitter and receiver
on the same frequency), one should check for activity on the channel before transmitting. This can
be done by checking the state of the DCD output. In addition, the unit can be programmed so that
transmit operation is inhibited if the DCD threshold has been exceeded.
CTS Output
The CTS (Clear To Send) output goes to its true state when the unit has powered up the
transmitter, is locked on the correct transmit frequency, and is ready to accept modulation. This
output may be used to signal a modem to start transmitting data. If this output is not used, to
avoid loosing data, a delay of at least 15 ms is required between PTT/RTS activation and the
application of data.
Transmitter Audio Inputs
Two audio inputs are available on the NL5000-T module. The AUX IN is a general-purpose input
that can have pre-emphasis enabled or bypassed and its gain can be controlled through
programming. The input impedance is greater than 50 kΩ and is capacitive coupled with a lower
roll-off frequency of about 25 Hz. The MIC IN input is fixed gain input designed for connection
to a standard electret or dynamic microphone. About 25 mV rms of input signal at 1 kHz will
produce 60 % of maximum deviation. The signal at this input is pre-emphasized. The signals at
both inputs pass through the modulation limiter and post-limiter filter.