Console-Mount User Station with A5F Headphone Connector


RTS' CM-300L is a console mount, two-channel intercom user station.  The user station is designed to be used in a full duplex, conference line intercom system.

NOTE: Shown above with A4F connector, though it comes with an A5F connector.


  • The volume control on the CM-300L has a wide range to compensate for: user hearing differences, ambient noise variation, variations in headset / handset sensitivity, and variations in voice.  The volume control in the CM-300L reduces distortion by driving the headphone amplifier only as much as needed.
  • In normal system operation, one or more users talk and the others listen.  A microphone switch on each station allows the talker's microphone to be enabled and allows the listeners to keep their microphones disabled.  In this condition, speech intelligibility is enhanced since background noise from other microphones is not present.  On the Model CM-300L, a toggle switch turns the microphone on.
  • A channel selector switch allows a choice of two (optionally three) channels. When the switch is on the "1" position the station talks and listens on channel 1, on the "2" position, to channel 2.
  • Pushing the Call Light button transmits a call signal to all other units on the channel selected by the channel selector switch.  A call signal on this channel will cause the call light push button to flash.  The flash rate is 2 to 5 times a second.  The call signal itself is a 20 kilohertz signal.


  • Input DC Voltage:
    TW Mode: 18 to 35 volts DC
    LP Option: 15 to 35 volts DC
    Battery: 12 to 35 volts DC (reduced performance)
  • DC Current Drawing from TW Line (Note: LP Option draws no current from TW line):
    - CM-300/RM-300: 23 milliamperes ±10%
    - CM-300/RM-300L: 33 milliamperes ±10%
    Operating 25 Ohm headphones:
    - CM-300/RM-300: 37 milliamperes ±10%
    - CM-300/RM-300L: 45 milliamperes ±10%
    Operating 25 Ohm headphones + Call Light:
    - CM-300/RM-300: 60 milliamperes ±10%
  • Impedance Across Line: 10,000 ohms, minimum
  • Operating Temperature: 0°C to 60°C
  • Storage Temperature: -40°C to 85°C
  • Operating and Storage Humidity: 5% to 95% non-condensing
  • Noise Contribution:
    One Unit: -75 dBu
    Ten Units: -67 dBu
  • Microphone Preamplifier:
    Input Impedance: 470 ohms/dynamic mic
    Source Impedance: 200 ohms, nominal
    Maximum Input Level: 150 millivolts
    Frequency Response: 100 hertz to 10 kilohertz ±3 dB (-54 dBu input)
    Limiter Range: 30 dB
    Carbon Mic Excitation Current: 10 millliamperes, nominal
  • Current Source:
    Transfer Ratio: 3.3 milliamperes/volt=3.3 millisiemens
    Output: ±5 milliamperes into 200 ohms = ±1 volt peak, nominal
  • Headphone Amplifier:
    Voltage Gain: 34 dB
    Output Voltage: 8 volts peak-to-peak into 25-1/2
    Output Power: 1/2 watt peak into 25 ohms
    Frequency Response: 150 hertz to 8 kilohertz ±3dB
    Headphone Impedance Range: 25 to 600 O (600 to 2000 with reduced levels)
    Note: Do not use headphones with impedance less than 25 O.
    Sidetone Adjustment Range: -20dB to full on
  • Call-Light:
    Signaling Frequency: 20,000 hertz ±100 hertz
    Flashing Rate: 5 hertz ±2 hertz
  • Auxiliary Connections:
    Headset Connector
    - Dynamic Microphone: XLR type 4-pin female
    - Carbon Microphone: 1/4"standard phone jack, 3-circuit
    Live Connection
    - Input: XLR type 3-pin female
    - Loop/External: XLR type 3-pin female
    - Dimensions: 2.75" (69.9mm) high, 6.25" (158.75 mm) wide, 6.4" (162.6mm) deep
    - Weight: 1.2 lbs (0.55kg)
    - Finish: Front Panel: Light Gray Enamel Paint
    - Federal Standard 595A Color#26492
    - Chassis: Gold Iridite over aluminum

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