The following circuits will allow remote control of the composite audio feeding an FM transmitter. This circuit could be simply modified for use with an AM trannsmitter as well.
This setup was useful when relocating studios and replacing an old STL system. Telos Zephyr ISDN codecs were used to feed the transmitter while rewiring and other STL equipment was moved or repositioned. Studio audio is fed into the studio end (transmit side) of the one Zephyr. The transmitter site unit (receive side) feeds a processor/stereo generator. You dial from the studio end unit and once the units sync-up, you can throw the toggle switch shown in the drawing. This will pull in the coaxial relay at the transmitter site end bypassing the normal STL link. Work on the primary link can now be performed.
This particular circuit used a Dow-Key SPDT BNC style relay with a 12V DC coil. The 12V power supply was a wall wart style unit from Radio Shack. The switch on the sending side was a SPDT locking style toggle switch used to minimize accidental operation.
Note: Warn the studio operator that the on-air audio will now be slightly delayed and it might be necessary to monitor the console program until the transmission system is put back to normal.
This remote control function of the Zephyr only works when the unit is in Layer 3 mode.
|Zephyr Parallel Port Pinout|