Radio Glen Transmit Selector system
Posted on Aug 2, 2012 12561
Under: Switching Circuits
The main box of the Transmit Selector system is designed to be located in the technical rack of a small radio broadcast station. There are four stereo balanced line inputs, either of which can be routed to a stereo balanced output. The signal routing is performed with relays and so the switching may not be completely silent. The source is selected by one of four buttons on the main box or by an identical pattern of buttons on one of three remote control panels. The particular panel which can control the switcher at any time is the panel which has the 'ACCEPT' lamp lit. This works on the standard offer-accept system as widely used on mixing desks and switchers. The main switch unit also has an 'OVERRIDE' button which can be used to force the system into offer mode regardless of whether the main panel has control.
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The main panel can therefore steal control when needed, and this also serves to reset the system on delivery or when the latching relays have been set to an unknown state by vibration in transit. Also, if a remote panel has control and is subsequently disconnected, the system can still be switched from the main panel using override. Remote panels connect to the main unit via a sixteen way cable terminated with 25-way D-connectors. All power for remote lamps is provided along this cable. Both main units and remote panels are 2U size, though this is only due to handy small boxes for the remotes only being available in 2U size. Future units could be 1U if suitable hardware can be found. The main unit will have to remain 2U due to the number of connectors on the rear panel. All switch lamps are LED types. Sheet two has the four state relays which record which panel has control, ie the accept lamp lit. The common ground of each remote panel's select switches are routed through the appropriate relay, so only one remote has control. The fifth relay on the sheet indicates the offer state and allows any remote panel to alter the state of the accept relays. Note that when one panel selects its own accept relay to go on, it switches all the others off via the diode ORing arrangement, ensuring that only one panel can ever accept control. SOGNDx is a potentially confusion label; It stands for SELECT/OFFER GND and is low for the panel...