Signal examination¶

The features described here are not needed for the lightning detection and station operation itself. But they can be very useful for optimization, for research and deeper analyzing.

Live Signal view¶

The Signals page allows seeing the waveform of the received sferics, interference signals or background noise, even if they are not sent to the servers. However, not all signals may be displayed for performance reasons, especially if many consecutive signals are received within a short period of time.

If the time stamp appears green, the signal has been released for transmission. It appears red if it has been marked as invalid, e.g. due to filters or lack of GPS reception. Signals from noise floor have a black timestamp.

The image above shows a very weak pulse in the first channel (red) that is only slightly stronger than the background noise. The second channel never reached the threshold, so it is marked with an L (more). The timestamp appears green because it has been released for transmission and is not marked as invalid. DSP filtering has been made and frequency spectrum is available at least for the first channel

Frequency spectrum¶

The frequency spectrum is only visible under the signal when the DSP is enabled and a signal has been transferred which was previously analyzed by the DSP filter. Signals of channels which have been sorted out by other filters may not contain a frequency spectrum. The frequency spectrum may also not be available for signals in quick succession, because due to limited on board memory the buffers are already occupied by the next signal, when the browser requests it. Those buffers not needed by the actual DSP processing itself and could even be disabled by the filter in case more memory is needed for other purpose.

If the Auto Voltage checkbox is activated, then the amplitudes of all channels are normalized regarding the most powerful frequency bin (which will be 100%). Otherwise the highest ever transmitted amplitude until the whole page is been reloaded will be the reference.

The noise floor frequency spectrum is the moving average of the last couple of noise signals (10 by default, see "Noise Smooth" on status page). If the noise overlay is activated, then this noise floor spectrum is overlayed on the currently received signals spectrum with dark grey. In other words: The leftover colored spectrum is the energy of the received signal/sferic.

The frequency bands can also be shown in the spectrum. They are even available when the spectrum couldn't be transmitted (i.e. due to lack of buffers).

The frequency bin width varies with the FFT resolution. More information can be found in the description of the DSP filter.

Audio Playback¶

Wave audio streaming¶

With this feature the browser or an audio player app can receive the original sampled data for each amplifier channel as a standard WAVE stream individually. This allows hearing and/or deeper analyzing the actual incoming signal from the amplifier. That may help identifying local disturbers and thus allows better placement of the antennas.

The sample rate can be adjusted individually but it should be a integer divisor of the original A/D converters sample rate. In case of the default ADC sample rate of 500kHz you may use 50kHz (1/10) or 31.25kHz (1/16). The ADCs default resolution is 12bit, so for 8bit output the lower 4bits are removed and for 16bit the signal is "amplified" by 4bits to use the full dynamic range.

The audio stream can be played in the browser window. This may not work at on mobile devices as they don't seem to support WAVE streaming and the ADPCM format does not work even on desktop browsers. Software like VLC ⧉ can play all those formats and is available for almost every type of device. Also note that only one stream is possible. When requesting a new stream while another one is running the old one will be terminated.

Due to buffering on your local device the stream will always have a delay of some seconds. So if you want to optimize an antenna position, and you just moved the antenna, then wait a few seconds.

For optimal streaming experience:

• Close any other browser windows which accesses the web interface
• Use low latency connections to connect to your station (direct LAN, high speed WiFi - no VPN, Internet)
• Use single channel and ADPCM format for high sample rates
• Stay below 1.5Mbit/s
• Disable filters*
• Disable thresholds (set to 0)*
• Lower ADC sample rate*
• Use monitor mode (disable server communication)

* Remember to set them back after streaming!

Usage with SpectrumLab¶

SpectrumLab ⧉ is a spectrum analyzer software for Windows with Waterfall Display and real-time audio processing provided by DL4YHF.

There's currently no option to directly send the stream ⧉ to SpectrumLab (but it is planned). To see and process the audio stream in SpectrumLab (or any similar software) you have to use the mixer input as recording device (which may not be available on every sound card). Then simply open and play the stream with VLC and select the sound card in SpectrumLab. Then you can apply different filters and further process the received signal. You can even play and hear this signal with another sound card.

Buzzer playback¶

This feature is just for fun or for demonstration purpose. It has been there long before the ability to transmit an high quality audio stream. The quality of the buzzer playback is far worse. Just select one or more channels and start the playback. You may need to adjust the volume if you hear nothing or too much noise.