TELCO & CELLULAR INTERFACING

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800-287-6867
301-754-2871

Telco Interfacing

For sending or receiving audio on telephone lines, an interface is required. Which type of interface you need depends on the type of phone connection you have, and whether you need to route audio in one direction or both.

The simplest type is a handset interface that takes or feeds audio from the handset wire on a standard two-piece telephone set. Handset interfaces are suitable for routing audio in one direction only, either send or receive, but not both simultaneously. (Ex: - JK Audio That-2) Until recently, this was the only option when working in an office environment with a digital phone system (see below).

A typical line interface is a Coupler. Varying in features from model to model, they can be as simple as a transformer coupled input/output box (which blocks DC voltage and “holds” the connection), to a full featured box with a dial pad, mixer, meter, & multiple inputs & outputs. Couplers are suitable for routing audio in one direction only, either send or receive (as in a listen or IFB line) but not both simultaneously. (Ex: JK Audio CommPack)

A telephone Hybrid is the only interface suitable for simultaneously sending & receiving audio (two-way conversation). Since telephones send and receive audio on a single wire pair, couplers and handset interfaces cannot separate them. Hybrids have either multiple transformers or active circuitry that provide 20dB or more separation between the two audio paths. There are analog hybrids & digital hybrids. Digital hybrids automatically self adjust for changes in telephone line equalization, impedance, side-tone level, and more. Analog hybrids have manual adjustments.

Typical hybrids are connected to a standard dial tone line. They cannot be connected through digital phone systems commonly found in offices. However, JK Audio has developed hybrids that connect like a handset interface on digital key or PBX (office) phone systems. It improves the separation between the send & receive audio paths.

JK Audio has also developed multiline digital hybrids and IFB couplers for both field use (VNR’s, SNR’s, O&O interviews, etc.) and for rack mounting in a studio or production truck, able to simultaneously handle two or four separate phone lines.

JK Audio

Cellular Interfacing

A “Fixed Wireless Terminal” is an interface between cellular RF service and a standard hard wired phone or phone system. It is essentially a specialized cell phone that simulates lind line telco service to provide dial tone and control signals for wired phones.

A typical application is in mobile production trucks for IFB feeds and coordination phones.

Another application is phones for temporary production offices. One or more FWT’s can travel with the production staff to provide production office phones with the same phone numbers in every location.

There are two main types of cellular services - GSM & CDMA. A cellular carrier will provide one or the other, and you would select the FWT for the carrier you use.

GSM service subscriptions utilize SIM cards, which are inserted in a phone or terminal. A SIM card can be taken from a cell phone from any GSM carrier & inserted into the FWT to make that service available on an entire phone system.

CDMA service subscriptions are tied to a single phone instrument through the use of an Electronic Serial Number. An FWT for CDMA would require it’s own service subscription.

External antennas, mounts, splitters, and RF amps are also available.

Telular for GSM Service

Telular for CDMA Service