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Guard DogGuard Dog

The Alice Guard Dog is an intelligent programme monitor and source selector using the latest micro-processor technology. The Alice Guard Dog is ideally suited to Studio Transmission links where programme integrity can be maintained even in the most extreme cases of source interruption. Situated at the receive end of the link, the Alice Guard Dog continuously monitors three sets of electronically balanced stereo inputs, prioritised main, standby and local. A failure of left or right audio only will quickly result in a mono feed to both outputs. In the event of complete audio input failure of the main feed the Guard Dog will switch to the standby source. Comprehensive logic outputs allow the Alice Guard Dog to trigger an auto-dialling ISDN CODEC if necessary. Remote telemetry can also be alerted of the failure.

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In the event of the standby service suffering problems a third source is available. The Alice Guard Dog can operate an on-site CD player (single or multi-disc), cycling however many discs are available. In this way, however the duration of the fault, embarrassing periods of 'dead air' can be completely avoided. An internally selectable extra 10dB of input gain accommodates semi-pro equipment so, for shorter periods, a simple cassette player can be used. If at any point the main or standby services are restored, they are immediately routed back to the output. Both standby and local overrides are available allowing user intervention via either telemetry or on-site.

High-quality solid-state switching is employed, with the audio path remaining balanced throughout for minimal signal degradation. Selective filtering allows enhanced discrimination between valid audio signals and noise produced by source failure, preventing spurious source changes. Inputs and outputs are via Neutrik XLR connectors, which may be wired unbalanced if required and the mains input is via an IEC. The Guard Dog is supplied with a 2m mains lead and an eight year warranty.


Technical Specification
Modes of operation
Main S: main stereo input to stereo output
Main L: left channel of main input routed to both output channels
Main R: right channel of main input routed to both output channels
Standby S: standby stereo input routed to stereo output
Standby L: left channel of standby input routed to both output channels
Standby R: right channel of standby input routed to both output channels
Local: local stereo input routed to stereo output
The unit respond to any fault with corrective action within 60 seconds

Audio input: balanced stereo female Neutrik XLRs
Audio input impedance: 20k ohms
Audio outputs: balanced stereo male Neutrik XLR
Audio outputs impedance: <1 ohm

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 and logic I/O
Local control: 9 way male D-type with START and STOP pulses
available on uncommitted opto-isolated transistors.
+12V and OV are also available
Logic I/O: 15 way male D-type connector carrying:
10 x open-collector outputs rated at 30V, 50mA
POWER ON output (closing pair to OV)
POWER OFF output (closing pair to OV)
STANDBY OVERRIDE input (+5 to +18V, active,< 1mA)
STANDBY OVERRIDE input (closing pair to OV)
Case details: 1U 19" rack mounting, overall depth 165mm
Mains voltage specification: 110/115v AC 60Hxz or 220/230v AC 50Hz 10VA
Dimensions: 465(w) x 165(d) x 44(h)
Weight (boxed): 2.1kg