Telephone System Coupler-CO Line Simulator

The RDL ST-TC1 Telephone System Coupler is designed to simulate a Telco CO line while providing audio and control connections for telephone-based systems. It can connect to a local telephone switch or instrument, add radio control or paging to a KSU, provide contact closure when the line is off-hook, and support audio input and output from a telephone switching unit. Its compact dimensions make it suitable for installations where space is limited.

Ideal Use Cases

The ST-TC1 is suited to systems that need CO line simulation without a conventional Telco connection. It can interface with a local telephone switch or telephone instrument and can be used when adding radio control or paging functions to a KSU. The off-hook contact-closure function provides a control signal when the connected line is in use. Audio input and output capabilities also allow the module to exchange audio with a telephone switching unit.

Why Choose This Model

This model combines telephone-line simulation, audio interfacing, and control outputs in a module measuring 0.7 inches high, 3 inches wide, and 1.6 inches deep. The specified mic input is a 5 kΩ unbalanced line with adjustable sensitivity from -80 dBu to -50 dBu. The 200 kΩ unbalanced line input offers adjustable sensitivity from -45 dBu to -15 dBu. An audio-threshold LED is provided for setting sensitivity.

Control options include an open-collector output rated at 25 mA, suitable for driving indicators or a Slave LCR, and double-pole, double-throw relay contacts. The listed maximum switching power is 60 W, with ratings shown as 220 Vdc, 125 Vac, and 2 A. These connections provide both relay-based and open-collector control paths for integration with compatible equipment.

Installation and Integration

The ST-TC1 requires ground-referenced 24 Vdc at 50 mA. The stated requirement assumes a maximum 20 mA load at the SLAVE output. A power supply is not included; the recommended models are the PS-24AS for the USA and the PS-24AX for international use. The specified ambient operating range is 0° C to 55° C.

Its compact enclosure dimensions are 0.7 by 3 by 1.6 inches, equivalent to approximately 1.7 by 7.6 by 3.9 centimeters. Before integration, the installer can use the audio-threshold LED to set input sensitivity for the connected audio source. A specification-sheet PDF, functional block CAD file, and front and end panel diagrams are identified in the supplied product data.

Performance Highlights

The module has a 50 ms retrigger delay. Relay-contact activation response time is specified at 5 ms, while the Slave open-collector output response time is 3 ms. The relay-contact release delay is adjustable from 70 to 260 ms. The Slave open-collector release range is adjustable from 15 to 260 ms.

Separate mic and line input sensitivity ranges accommodate different incoming audio levels. The mic input adjusts from -80 dBu to -50 dBu, while the line input adjusts from -45 dBu to -15 dBu. The threshold indicator provides a visual reference during sensitivity adjustment. Control can be taken from the DPDT relay contacts or the 25 mA open-collector output, depending on the connected system.

What Makes It Different

The ST-TC1 brings together functions that directly support telephone-system integration: Telco CO line simulation, local telephone switch or instrument connectivity, KSU radio-control or paging integration, off-hook contact closure, and telephone switching-unit audio input and output. Its combination of adjustable audio sensitivity, relay contacts, and open-collector control provides multiple interface points within one compact unit.

Final Assessment

The RDL ST-TC1 is a focused solution for telephone, paging, and radio-control installations requiring a simulated CO line and off-hook control. Its adjustable mic and line inputs, DPDT relay contacts, 25 mA open-collector output, documented response times, and compact form factor provide concrete integration options. Installations must supply the specified ground-referenced 24 Vdc power source.