This guide shows how to check, with a software-defined radio ( SDR) or a portable spectrum analyzer, whether a TVWS device is actually emitting a signal on the configured channel. It is a simple check, done before investigating more complex problems. In Tururi, it was the first step of the installation.
What you need
- A HackRF with PortaPack, a TinySA or another instrument able to display the spectrum between 470 MHz and 698 MHz.
- An antenna for the instrument suited to this band.
- The center frequency and channel width configured on the TVWS equipment, which can be checked in its management interface.
Steps
- With the TVWS radio switched off, tune the instrument to the center frequency of the channel and set the displayed range (span) to about 10 MHz. This way the whole channel and a little on each side are visible.
- Record the background spectrum: the signals and noise already present there. If the channel is already occupied by another signal, write it down. It may be a source of interference.
- Switch on the TVWS radio and wait until it starts transmitting.
- Watch the channel. A digital data signal appears as a more or less flat block of energy, filling the width of the channel, above the background noise.
- Confirm by sound, if the instrument allows it. On the PortaPack, the receiving apps of the Mayhem firmware play the signal as audio: a continuous hiss that appears when the radio is switched on and disappears when it is switched off indicates transmission.
- Repeat for each antenna of the base station, if there is more than one.
What the result indicates
- There is a signal on the right channel: the radio is transmitting. If the link still fails, the problem is in the signal’s path, in the receiving antenna or in the configuration.
- There is no signal: check the power supply, the channel configuration and the connections between the radio and the antenna.
- The signal appears on another frequency: check the channel configuration in the management interface.
See also
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