covert@covert.enet.dec.com (John R. Covert 20-Jan-1991 1858) (01/21/91)
From: John Keator, Telcom, National Public Radio, Washington Date: 20 Jan 91 Subject: CNN Communications A four-wire circuit is just that, two separate circuits for send and receive. It is very commonly used in broadcasting to connect a remote site to the main studio. Often several circuits will be set up: one for production use between the producer/director and another for engineering. Normally, the lines are connected to a so-called four-wire box, actually a small device made by Prospect Electronics in the UK, that allows the incoming line to be heard in a speaker/headphones and has a push to talk switch that allows the remote to talk to the studio. In addition, the box has a conferencing arrangement so that a second four-wire can be connected and the box can be optioned to allow the user to talk to either four-wire or both ... in the both position the two four-wires are linked together so everyone can hear and talk to everyone else. They are much in evidence on the recent shots from the middle east of technical setups in the various bureaus. They are about the size of half-a-loaf of bread, have a speaker and yellow and orange switches on the front and a gooseneck microphone on the top. In normal usage the program audio travels on a separate wide-band circuit to the studio either on a land line or satellite. The programing four-wire is normally used for IFB, interuptible feed back. This is fed to the small earpiece the reporter uses that allow him to hear the program on the air, less his own voice (due to satellite delay). In addition, the director at the studio can talk to the reporter telling him to cover a certain issue, throw it to another location or end his report. When not on the air the circuit is used for coordination and planning upcoming segments. In the CNN case, they had ordered the four-wire to Amman months ago for coordination on earlier satellite feeds. These feeds were not available, but the coordination connection was not disconnected and was put on the air for the famous broadcast. They did not use an Inmarsat portable uplink at the hotel; no one did that night, as they did not want to be sending radio waves in to the sky with all the missiles flying around ... who knows what they might home in on. The next day the BBC used one from the garden of the hotel, but I believe it was later confiscated. Legally, you need prior permission from the country to use an Inmarsat terminal for land mobile use, but many news companies had sneaked them in. John Keator NPR Work: 202 822 2800