RTS SPK-300 Portable Speaker User Station with Shure 577B Microphone

Used – Acceptable: The item was removed from a working system. It is still functional in that, it still powers on. We are unable to verify any further functionality. Bears signs of wear such as scratches, dents, worn corners, or identifying markings. Parts, accessories, and instructions may be missing. Sold as is.

NOTE: Does not include power cord, power supply or any other items not in the photos.

The RTS SPK300, portable speaker user station, is a component used in the TW (two-wire) Intercom System. Each user staion is a communications unit along a multi-unit conferece bus.

The SPK30 User Station interconnection can be: 1) centrally wire, with each cable coming from central point, or 2) distributed, where all the user stations are looped togehter from one to another, or 3) a combination of both. The centrally wired interconnection not only reduces interchannel crosstalk, but also allows for eaiser expansion into an assignable channel, multi-channel system.

COMPONENTS

• A Microphone preamplifier with limiter
• An Electronic microphone switch
• A "Bilateral current source" line driver
• A Listen volume control
• A Headphone amplifier
• A Speaker amplifier
• A Speaker switch
• A Channel selector switch

The Microphone Preamplifier/limiter – converts the small microphone signal to a strong line level signal conditions the signal strength from loud and soft talkers to be almost the same sends the signal to the line via the microphone switch and a "bilateral current source".

The Bilateral Current Source – adds signal, via the channel select switch, to the line without affecting any signals already on the line. The bilateral current source also extracts the listen signal from the line and sends it to the headphone amplifier via the volume control. Some of the user's own voice signal ("sidetone") is also fed to the headphone amplifier.

The Channel Selector Switch – selects the channel on which the user will talk and listen. The headphone amplifier output drives the user's headphones.

The Volume Control – also feeds the speaker amplifier via the speaker switch and the speaker dim network.

The User Station Voltage Regulator – takes power from channel 1, regardless of the channel selector switch setting (exception: local power option units). The regulator not only supplies regulated power to the user station, but also prevents unwanted interaction between the user station and the intercom line which is supplying the power. Because the regulator takes power from channel 1, channel 2 can be expanded into many channels by using a switch and, for each channel, a separate wire and a termination network consisting of a 200 ohm resistor and a 10 microfarad capacitor in series.

A TW System Power Supply terminates a line with 200 ohms.