R&S 4200 Series Operating Manual page 134

R&S XU 4200
3.8 In-Band Signaling
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In-band Signaling\In-band Signaling "Radio".doc
This chapter
3.8.1 Introduction/Overview
Introduction
Signaling of PTT PTT can be keyed by a tone with a specified frequency that is present within
AF signal. If the parameter is ON, the in-band tone is detected and controls the
PTT function. The tone itself is suppressed within transmitted signal by a notch
filter. The PTT can be signaled via the TX audio channel with the tones of 2040
Hz, 2300 Hz, 2970 Hz or 3100 Hz.
Signaling of SQ
Audio in-band
tones for RSSI
signaling
6166.5368.02.01
This chapter provides information about the functioning, configuration and
conditions of the radio for the in-band signaling.
To reduce the number of lines, in particular for transmitting signals over long
distances, the use of the bidirectional in-band technique via a 2-pair
AF/telephone line per radio unit (receiver, transmitter or transceiver) is
recommended.
The R&S Series 4200 radios support the following in-band functions:
 Signaling of PTT on transmitter side
 Signaling of SQ on receiver side
 Audio in-band tones for RSSI signaling on receiver side
SQ can be indicated by a tone with a specified frequency that is present within
AF signal. If the In-Band signaling is configured to SQ, the in-band tone is
generated when SQ is open (SQ threshold is met). If the parameter is
configured to INVSQ, the in-band tone is generated when the SQ threshold is
not met. A part of AF signal near the SQ tone frequency is suppressed by a
notch filter. The squelch can be signalled via the RX audio channel with the
tones of 1225 Hz, 2040 Hz, 2175 Hz, 2440 Hz, 2970 Hz or 3300 Hz.
The level of the SQ tone is variable within specified range and is related to
nominal audio signal level set by "RX Audio Level".
At the RSSI selection one of four tone frequencies is generated depending on
received signal strength and is transmitted via the in-band audio channel
(X10.2/X10.3) (see Fig. 3.79 Tone used for RSSI signal quality). The
appropriate low pass filter is used in order to suppress received AF signal in
the affected AF range. During one transmission cycle the RSSI signaling
frequency is kept constant. The level of the RSSI tone is variable within a
specified range and is related to nominal audio signal level.
Note: Once the SQ criteria is met, the signal strength is evaluated. An
appropriate in-band tone is selected and kept unchanged for the whole period
(until the SQ release).
3390 Hz (good quality)
3300 Hz (middle quality)
3210 Hz (bad quality)
3180 Hz (no signal)
Fig. 3.79 Tone used for RSSI signal quality.
SQ criteria met, RSSI > 30 µV
SQ criteria met, 6µV < RSSI < 30 µV
SQ criteria met, RSSI < 6 µV
SQ criteria not met
3.82
In-Band Signaling