How they work

How do Talking Head Units work?

The system normally consists of two units a ruggedised field unit, the TH-1 or TH-2 and a rack mounted studio unit, the TH-R. Although we sometimes refer to these as transmitter and receiver the system sends video and audio in both directions at the same time, so a reporter can not only hear the studio he/she can see the studio output too. Incidentally, a mobile unit can be used at the studio and a rack mounted unit in the field, perhaps in an OB truck for reverse vision.

The system can either use one channel (line) of an ISDN-2 to operate at 64 kbps or by making two calls 128 kbps. The higher data rate allows the system to cope with more movement in the picture, or if desired improve the audio quality to studio standard (48 kbps rather than 16 kbps) in lieu of a smaller improvement in the picture quality.

Studio Infrastructure

At the receive end you will need an ISDN-2 line which presents an S0 interface, this is normal in Europe (Euro-ISDN) and most of the world. However in the USA, and a very few other countries, ISDN lines are presented as a U interface (one level back from S0), this means a device known as an NT-1 is required, your telco or a good local telecomms supplier can supply these.

Field Infrastructure

In the field you will need either:

an ISDN-2 line, typically in the bureau, at the correspondents home or maybe at a hotel business center or press bureau, from which you can connect at either 64kpbs or for better quality at 128kbps - both data rates are supported by all the Talking head units.

OR

An Inmarsat GAN satellite terminal which provides an ISDN-2 interface but is only capable of single channel operation (ISDN-1!) so can only connect at 64 kbps, with any model Talking Head unit.

OR

Any TWO Inmarsat GAN satellite terminals each of which can provide 64 kbps and a TH-2 which incorporates the 7E S0DA duo technology to split the two channels of a 128 kbps ISDN-2 call across two single channel ISDN interfaces, ie two satphones.

Note: One satphone manufacturer makes a dual channel GAN (very bulky) and another has a terminal to terminal interconnect cable, in both cases a TH-1 can make 128 kbps calls.