Product ordering code: MRU1
The MAC Relay Unit is a passive box with relays, which allows the Davicom MAC to switch between primary, secondary and tertiary audio without the need for separate audio and RF switching systems.
It is designed for transmitter sites where there is a main audio link (landline, microwave, etc.), a back-up link (UHF, VHF, etc.) and a local CD or MD player in case of total audio failure. The CD/MD input (RCA phono sockets) has variable gain to bring the level up to line level. There is also a low power (up to 100W) RF co-axial relay to switch exciter drives.
The usual audio configuration is as a switcher to preserve a feed to a transmitter, diverting to a secondary or even tertiary audio source if the telemetry detects a failure in the primary path, or to the good channel if one leg in a stereo paths fails. On the RF side, if the telemetry sees a failure in the “A” chain exciter it can switch to the standby "B" exciter.
The unit uses conventional relays as audio switching elements, so imparts no noise, distortion or headroom limits to the signals passing through, and is completely bi-directional. The "normal" signal paths will also be maintained in the event of a power loss.
The switching of the co-axial RF relay is controlled in a timed sequence, so that muting signals may be applied to the transmitters to avoid the possibility of driving into open or shorted outputs.
The unit comes in a 1U, 19-inch rack-mount case. Audio connections are by XLR (primary, secondary and outputs) and phono (tertiary). RF connections are N-type (common) and TNC (switched). Power requirement: 12 VDC.
Main benefits:
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Inputs and outputs (except RF and tertiary audio) are on XLR connectors, a world standard;
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One relay can switch stereo balanced audio, instead of using four in the MAC unit;
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RF can be switched;
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The MAC unit can be removed without losing through audio connections;
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If the MAC Relay Unit needs to be removed the audio XLRs can be unplugged and connected together to maintain the primary audio channel.
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