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Set up a TVWS test bench with attenuators

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Set up a test bench

This guide shows how to connect a TVWS base station to one or more CPEs by cable, without antennas, to check that the equipment works before taking it into the field. It was the first step of the tests in TECER’s Phase 1, before the field test in Mosqueiro.

Why use cables and attenuators?

Connecting the radios by cable removes the variables of the environment: distance, vegetation, interference. If the system fails on the bench, the problem is in the equipment or the configuration, not in the signal’s path.

Attenuators are essential. Without them, the signal from the base station would reach the CPE much stronger than on a real link, which can saturate the receiver or even damage it.

What you need

  • The base station and the CPEs, with their power supplies.
  • Short coaxial cables, with connectors compatible with the radios.
  • Fixed RF attenuators, with the same impedance as the radios (usually 50 ohms) and able to handle the transmission power.
  • A power divider (splitter), if you will connect more than one CPE to the same port of the base station.
  • 50 ohm loads for any antenna ports left unused.
  • A computer connected to the network on each side, to test data transfer.

Steps

  1. Check the datasheets. Write down the maximum transmission power of the base station and the maximum input power the CPE can handle. The difference between the two, plus a safety margin, indicates how many decibels of attenuation are needed.
  2. With everything switched off, assemble the signal path: base station antenna port, cable, attenuators, divider (if any), cable, CPE antenna port. Place the attenuators closest to the transmitter.
  3. Close the unused ports with 50 ohm loads. Never switch on a radio with an open antenna port, with no antenna and no load.
  4. Switch on the base station first and then the CPEs. Watch the indicators on each device until the link is established.
  5. Check the received signal level in the CPE’s management interface. It should be within the range recommended by the manufacturer. If it is above that range, add attenuation.
  6. Test data transfer, not only the connection between the radios: send traffic from one computer to the other and, if there is internet access, check that the traffic reaches it.
  7. Record the configuration, the attenuation values, the signal levels and the behavior of the indicator lights.

Common problems

  • Indicator lights that do not match the manual. In Phase 1, the manufacturer’s material did not explain all the light patterns. Record what you observe and confirm with support.
  • Mismatched network addresses. Check that each device received the expected address before testing traffic.
  • Unstable connection even with a cable. Check the attenuation: a signal that is too strong also causes instability.

See also

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