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Line Level Stereo Audio Transceiver With Serial Data And Controls (E&M)

Model #: FOI-7280



Elegantly simple yet packed with an advanced feature set, the FiberPlex Technologies, FOI-7280 is a powerful problem solver when it comes to routing audio or transporting E&M signals. The unit converts line level, stereo analog audio to fiber for long or short haul transport. In addition to the audio, a multi-format serial data connection and a bidirectional pair of contact closures are included. The combination of audio and signaling provides a seamless solution for 4-wire E&M applications.

What’s the difference between the FOI and the TD versions?

Functionally, the FOI-7280 and TD-7280 are identical. The only differences are the packaging and power supply. The FOI-7280 is part of the FOI line of products designed for ruggedized military applications while the TD-7280 is housed in the commercial ‘Throw Down’ packaging.
  FOI-7280 TD-7280
Standalone Power Requires a PSQ-4909 AC supply or PSQ-4920 DC supply Power Supply included
Power Connection High Reliability Lemo™ connector Both circular DC connector and 3-postion Phoenix™ quick connect
Chassis Mounting Uses the RMC series chassis for up to 9 units in 2U or 8 units with redundant power supply 6 units in a 1U with the optional TDR-01-AC
Case Mil-style sealed steel can enclosure Durable anodized brushed aluminum


Various advanced routing and networking options are available via DIP switch setting. These include the following:

Point to point mode

Point to Point Mode

Basic configuration. Audio inputs one unit map directly to audio outputs on the other unit. Serial data and contact closures are a direct connection.  

Broadcast Mode

Broadcast Mode

One unit is configured as the master, which sets the clock and sampling rate. Analog and serial inputs to the master are sent to all the slaves, which output the data on their respective ports. No communication is sent from the slaves to any other units.   

Intercom / Loop mode

Intercom Loop Mode

One unit is configured as the master, which sets the clock and sampling rate. It polls the loop, with each unit in the loop adding its own input to the aggregated sample, gated by its push to talk, if enabled. When the sample returns back to the master, it then sends out that aggregated sample as the output for all units in the loop. All units forward the aggregated output around the loop until it returns to the master, which discards it. Serial data from the master is replicated on all slaves, and serial data from the slaves is aggregated to output on the master. 

Typical Applications

E&M Type IV Audio Tie Lines Intercom / Loop Railroad Signaling


Audio Interface:

  • Supports Balanced and Unbalanced Audio I/O
  • Supports E&M (Ear and Mouth) Types II-V
  • High Quality 24-bit audio
  • Ultra Wide 20 Hz to 45 kHz Frequency Response
  • Supports Ultrasonic Signaling

Serial Interface:

  • RS-232, RS-422, RS-485 (2/4 wire)
  • Data Rates from 0 to 1 Mbps

Contact Closures:

  • ‘Form C’ Contacts
  • Supports Push to Talk

Advanced Routing:

  • Point to Point
  • Broadcast Mode
  • Intercom/Loop
  • Multichannel Add/Drop


  • TD includes power adapter as well as a 3-position Phoenix™


  • Audio Tie Lines
  • Audio Distribution
  • Push To Talk
  • Intercom
  • Railway Signaling
  • E&M
  Min Typ Max unit
DC Response Linear Range -7   +7 VDC
Offset   20   mV
Gain Error -3   +3 %
Frequency Response 20 Hz to 25 KHz -0.5 0 0.5 dB
26 KHz to 45 KHz -1.5 0 1.5 dB
Third Harmonic Distortion plus Noise (THD+N)* - 1 KHz @ +4 dBu - 0.015 - %
Input Level (with max 1% THD) -60 0 +17 dBu
  -   VDC
Input Sensitivity 0.020 0.775 7 Vrms
Input Noise Floor ref +0 dBu - -80 - dBu
Input Impedance - 2 -
Output Level 0.02 0.775 7 Vrms
Output Impedance - 150 - Ω
Output for Use with Nominal - 600 - Ω
Audio Latency (point to point) - 1260 - µs
Sampling Rate 24 bit / 96kHz or 24 bit / 48 kHz
*Hum & Noise are measured with an AES17 compliant filter at 20 kHz. Temperature condition @+10 - +25° C.
  Min Typ Max unit
RS-422 / RS-485 Output Levels into 100Ω Load - ±2 - VDC
Input Levels -7 - +7 VDC
Input Threshold ±0.2 - - VDC
Data Rate 0 - 1 Mbps
Input Termination - 150 -
RS-232 Output Levels, 3KΩ Termination ±5 ±5.4 - VDC
Input Levels -15 - +15 VDC
Input Threshold ±3 - - VDC
Data Rate 0 - 1 Mbps
Input Termination 3 - 2.3 K Ω
  Min Typ Max unit
Shorting Actuation Voltage Threshold - 0 2.5 VDC
Load - 0 1
Negative Voltage Actuation Voltage Threshold -48 - -6 VDC
Load 2 - 25 mA
Relay Output On Resistance - 10 15 Ω
Off Resistance NO contacts 0.35 - 5000
Off Resistance NC Contacts 0.1 - 1.4
Voltage Limit 0 - 200 VDC
Current Limit 0 - 200 mA
  Min Typ Max unit
Environmental Storage Temperature (°C) -40 - 85 °C
Operating Temperature (°C) 0 - 50 °C
Power Requirement Voltage Range 7 9 24 VDC
Supply Current, no SFPs - 600 - mA
Phoenix™ Mating Plug 6 pos Audio/Serial/Control(PN 1778874) Wire Accepted 20 - 26 AWG
Nominal Voltage - - 160 V
Nominal Current - - 6 A
Phoenix™ Mating Plug 3 pos Power (TD Only)(PN  1827716) Wire Accepted 14 - 28 AWG
Nominal Voltage - - 300 V
Nominal Current - - 8 A
Power Adapter Connection FOI-7280 LEMO™
TD-7280 Standard 5.5 x 2.1 mm DC barrel, center positive
External SFP Interface Min Typ Max unit
Data Rate - 346 - Mbps
Recommended Jitter - 40 - Psec
Operating Voltage - 3.3   VDC
Maximum Current - - 500 mA
Optical Modules SFP MSA (SFF-8431, SFF-8432, SFF-8433) compliant slot, data rate 266 – 1.25 Gbps
Case Dimensions Length Width Height Weight
FOI-7280    (Size 4) 4.5 in (114 mm) 1.453 in (37 mm) 2.56 in (65 mm) 2 lb (0.9 kg)
TD-7280 4.5 in (114 mm) 2.75 in (70 mm) 1.66 in (42 mm) 0.4 lb (0.2 kg)
Standalone Operation  
PSQ-4909  Standalone AC Power Supply
PSQ-4920 Standalone DC Power Supply
WMA-3002 Wall Mount Adapter
WMA-2001 Wall Mount Adapter with ST Optical Patch
Chassis Mounting  
RMC-2101 2U, 19" Rack Mount Chassis. Holds up to 9 FOI Modules
CMA-2001 Chassis Mount Adapter for RMC-2101 Chassis. (1) per FOI Module required
PSM-2010 Spare Power Supply for RMC-2101
RP2 16 Channel Modular Bolt-On Connector Panel for RMC-2101
RMC-3101 3U, 19" Rack Mount Chassis. Holds up to 9 FOI Modules
CMA-3002 Chassis Mount Adapter for RMC-3101 Chassis. (1) per FOI Module required
PSM-3010 Spare Power Supply for RMC-3101
Industrial Solutions
RMC-3700  Environmental Enclosure for FOI Modules
CMA-3002 Chassis Mount Adapter for RMC-3101 Chassis. (1) per FOI Module required
PSM-3010 Spare Power Supply for RMC-3101

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