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TXMTXM-1 & TXM-2

The Alice TXM-1 and TXM-2 are mains powered 1U rack mount, single and dual AM transmitter monitors. They provide a one-box interface for state-of-the-art telemetry systems (i.e Gentner GSC3000) at unmanned transmitter sites, and include automatic backup source switching, allowing uninterrupted programming in the event of an Studio/Transmission link failure.

Switching between the two balanced inputs - main and standby - is achieved by a high-quality relay, keeping the audio path balanced throughout, and making audio degradation undetectable. The main input is constantly monitored for valid audio. Selective filtering enhances rejection of out-of-band frequencies i.e hum and noise. For extra flexibility the threshold level is user programmable on the front panel.

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In the event of a sustained STL failure, the TXM will automatically switch the transmitter feed to the standby source. At the same time a trigger signal (pulsed or continuous) is made available. This can be used to initialize a standby source, be it an auto-dial ISDN CODEC or an on-site CD player. When the TXM is satisfied that the main feed has been permanently restored (glitches and clicks are ignored) the source will be switched back. An alarm output keeps the telemetry informed at all times of the incoming line status.

Setting the TXM apart from a simple silence sensor are its RF monitoring facilities. 2Vrms RF sample (available directly from many transmitters) is fed to the TXM. An internal demodulator extracts both the RF carrier level, hence transmitter output power, and demodulated audio, which drives a second valid audio detector. Both have user-programmable alarm thresholds.

With these alarms visible via the telemetry, it becomes a simple task to deduce the source of any problem, be it failure of the incoming line, the audio processing equipment, or the transmitter itself.

Inputs are and outputs are via Neutrik XLR connectors, which may be wired unbalanced if required. Mains input is via an IEC connector.

 

Technical Specification
Input impedance of audio detector: 20k ohms
RF sample input: BNC female socket
RF input impedance: 50 ohms
Output impedance: Dependent upon source (direct relay switching)
Alarm outputs: 15 way male D-type socket
Signal Requirements and Timing Connect
Incoming line level: -20 to +24dBu (+8dBu typical)
Incoming audio fail threshold: -28 to +24dBu (factory set to - 20dBu)
Incoming audio fail alarm delay: 45 seconds of silence allowed before alarm raised
Incoming audio alarm clear delay: 5 seconds of valid audio required before alarm deactivated
RF sample level: 1.5 to 5Vrms (+3dBm/2Vrms typical)
Demodulated audio fail threshold: 7 to 80% average modulation (factory set to 30%)
Demodulated audio fail alarm delay: 45 seconds of 0% modulation allowed before alarm raised
Demodulated audio alarm clear delay: 5 seconds of valid audio required before alarm deactivated
RF carrier alarm threshold: -20 to + 3dBm (factory set to -17dBm)

Audio performance
Gain: dB O.5dB (selectable + 10dB on local inputs)
Distortion (THD): <0.005% (0dBu, 1kHz input)
<0.05% (0dBu, 100Hz - 10kHz input)
Noise: <-100dB (relative to +8dBu input unweighted)
Common-mode rejection: >50dB
Frequency response: 0.25dB (20Hz-20kHz
Crosstalk (L-R): <-100dB (100Hz-10kHz)
Max. signal level: +25dBu

Alarms
Available alarm outputs: Incoming audio fail (continuous)
Demodulated audio fail (continuous)
RF carrier fail (continuous)
Standby source start-up (selectable pulse or continuous)
Drive capability: Each alarm output is an uncommitted opto isolator output
transistor, rated at 30V, 10mA. Both 12V and 0V are
available at the output connector, allowing pull-up,
pull-down or other configurations.
Mains voltage specification: 230v AC 50Hz 10VA (115v available to order)
Dimensions: 445(w) x 165(d) x 44(h)
Weight (boxed): 1.85kg