6 ANALOGUE MODES OF
OPERATION
6.1 ANALOGUE CAPABILITY
In addition to the serial data path the URT500 has an audio interface for external modem connection.
This allows use with older systems that employ private wires with external V23 or Bell 202 modems.
It should be noted that the external audio path is AC coupled and so is not suitable for GMSK or multi-
level signalling at baud rates above 2400 baud.
6.2 EXTERNAL AUDIO & MODEM INTERFACE
The selection of internal modem or external audio operation is made using the configuration software.
If programmed for external audio the signal path can be programmed for flat or a pre/de-emphasised
response, for compatibility with older systems. The input/output levels can be adjusted using the
configuration software over the range of +3dBm to -20dBm into 600 ohms. Unless otherwise requested,
the default factory setting is –13dBm.
The external Rx audio can be programmed for muted or non muted operation in the absence of a
carrier.
6.3 KEYING THE TRANSMITTER IN AUDIO MODE
In the external audio mode there are two options for keying the transmitter; first using the dedicated
input pin on the interface connector, or secondly by using the Tone Operated Switch (TOX). The TOX
can be programmed to key the radio on detection of either V23 mode 2 or Bell 202 tones. Other tone
sets can be provided for, by special order.
6.4 PROGRAMMABLE AUDIO PARAMETERS:
6.4.1
INTERFACE & MODE
The Audio Mode selects the interface and path of the signals within the URT500 and when the 2/4 wire
port is used, it should either be set for :
6.4.1.1
Ex Audio-PTT
Selects the 2/4Wire Audio interface and external PTT (TX Enable) and routes the audio via internal
level amplifiers to & from the transmitter & receiver modules respectively.
6.4.1.2
Ex Audio-TOX
This is the same as the EX AUDIO-PTT but routes the audio input via a Tone Operated Switch (TOX)
which can be set to detect V23 or BELL202 formats. Detection of the selected format will key up the
transmitter and forward the incoming data. It should be noted that a pre-amble of 10-15milli-seconds
duration consisting of data, single tone or alternating will be required so the decoder can lock on and
activate TX enable.
6.4.2
FFSK TONE SET
In EX AUDIO-TOX the ART can either be set to detect incoming V23 or BELL202 tone sets.
6.4.3
LINE LEVEL
The interface level is normally factory set for –13dBm, but can be adjusted between –20 to +3dB from
the CALIBRATE MENU by following the instructions.
URT500 Manual
Page 21 of 42
Rev. C – 6 August 2008
