VSAT Modem: Working, Testing, and Manufacturers

A VSAT (Very Small Aperture Terminal) modem is a crucial component in satellite communication systems. It facilitates the transmission and reception of data between ground stations and satellites. Essentially, it converts digital data into radio signals for the uplink to the satellite and demodulates signals received from the satellite back into usable digital data.

Understanding the working principles, testing procedures, and key manufacturers of VSAT modems can help organizations optimize their satellite communication systems for reliability and performance.

What is a Satellite Modem in VSAT?

The modem used in VSAT applications is commonly referred to as a VSAT modem, or simply a satellite modem.

VSAT modems are available in different bands, based on the Intermediate Frequency (IF) ranges used in their construction. Typically, you’ll find VSAT modems operating in the 70 +/- 18 MHz, 140 +/- 18 MHz, or L-band (950 to 1450 MHz) range.

The following diagram depicts the modules used in the design of an L-Band Satellite Modem:

• Baseband part: This includes FEC (Forward Error Correction) modules such as Convolutional encoders & decoders, differential encoders & decoders, and scramblers & descramblers.
• Modulator & Demodulator: These handle the modulation and demodulation processes, respectively.
• Modulator module: Takes information as input and produces a modulated carrier as output at the IF frequency.
• Demodulator module: Takes a modulated carrier as input and produces information (voice/data) as output.

Synthesizers are required in VSAT modems to select different RF carriers as needed.

Variable RF attenuators are used to provide different attenuation or gain values for testing and maintenance of the VSAT network.

Switches are used for various baseband loopback and IF loopback testing purposes, as well as for troubleshooting faulty conditions of the VSAT modem.

Usually, VSAT modems interface with Multiplexers/Demultiplexers using RS422/V.35 interfaces.

VSAT Modem Testing

The VSAT modem is located between the baseband multiplexer unit and the RF ODU (Outdoor Unit) or RF Transceiver Unit.

The following tests are conducted during the maintenance and installation phase of a VSAT modem:

• Baseband Loopback: Tests the baseband part of the VSAT modem.
• IF Loopback: Tests the baseband as well as the modulator-demodulator IC of the modem.
• RF Loopback: Tests the entire modem, including the RF part of the VSAT terminal.
• Bit Error Rate (BER) testing: Conducted for both short and long durations.
• Voice call flow and data flow testing: Ensures proper communication through the VSAT modem.
• Functional tests: Performed under various environmental conditions (temperature, vibration, etc.).

VSAT Modem Vendors or Manufacturers

The following table lists some of the leading VSAT modem vendors and manufacturers:

Conclusion

In summary, VSAT modems play a pivotal role in facilitating effective satellite communication, particularly in remote and underserved areas. Their ability to convert data signals ensures seamless connectivity, making them indispensable for various applications, from broadband internet to enterprise communications.