Tutorial Spectrum explorer

Tutorial: Spectrum explorer (look, measure, sweep)

What it is. The spectrum explorer is a measuring tool with no decoder. You look at a band live (spectrum and waterfall), zoom and pan, put markers, select a region and read its occupied bandwidth, channel power, SNR and symbol rate, work through a converter or LNB, sweep a range to list the signals in it, and keep bookmarks. Use it to find out what a signal is before you choose a mode, to measure your own transmitter, or to look at satellite and microwave signals.

What you need

• Any radio. The mode asks for 10 Msps (so you see 10 MHz at a time with a fast radio) and works down to 250 ksps; the table covers 0.1 to 7250 MHz. The default centre is 433.92 MHz.
• An antenna suited to the band. For microwave or satellite, a converter or LNB (set it under Converter, below).
• No frequency list: you decide where to look. For orientation, the frequency database lists known stations and the band plans give ranges; the Bands overlay is in the Spectrum analyser.

Before you start

• The span you can see is limited by the radio's sample rate. For a wider look use the Sweep tab or the Spectrum analyser.
• Overload gives false signals. Keep the gain where the noise floor rises clearly but no signals appear and disappear with the gain.
• A DC spike sits in the middle of the view; do not measure on it.

Step by step

1. In the mode list open General & tools and choose Spectrum explorer (second line Spectrum, waterfall, sweep).
2. Set the frequency and press Start. The Explorer tab shows the spectrum and the waterfall.
3. Hover over the display for the frequency and level under the cursor. The ? button lists the controls:
   • click: put a marker (up to 8; Clear removes them);
   • double-click: tune there (centre);
   • scroll wheel: zoom around the cursor;
   • drag: pan (the radio follows when you leave its band);
   • right-drag or shift-drag: select a region to measure.
4. Select a region over a signal. The Region tab shows the measurements (below).
5. Press Identify this signal to record a moment of the region and work out the modulation, symbol rate and the mode it could be.

What you should see

• A trace with the noise floor along the bottom and signals standing above it; the waterfall below shows time, newest at the top.
• A status line: RBW, floor (the noise floor in dBFS), peak and input levels, and "converter ..." when a converter is set.
• Markers listed as M1, M2 ... with their level and the offset from the previous one.

Reading the plot and the Region tab

Row	Meaning
Bandwidth -3 dB	Width 3 dB below the signal's peak.
Bandwidth -26 dB	Occupied width 26 dB down; a ">" means the signal met the noise floor first, and the value is where.
Channel power	All the power in the selected region.
SNR	Top of the signal over the noise floor, per bin (the floor is shown too).
Symbol rate	For a flat-topped carrier (a digital signal), its -3 dB width is the symbol rate; the roll-off is estimated from BW-26 / BW-3.

• Noise floor: the level where no signal is. Measure signals against it, not against 0 dBFS.
• Peak hold (checkbox): the highest level seen per frequency; Reset clears it. Auto range adjusts the vertical scale. Span and RBW (resolution bandwidth) are drop-downs; Avg averages sweeps.
• For a satellite carrier Open in DVB-S/S2 hands the frequency and symbol rate to the DVB-S/S2 receiver (see DVB-S/S2).

Options and settings

• Converter: tick it when you have an LNB or converter before the radio. Then every frequency you see and type is the RF frequency. Presets: Universal LNB 9750 / 10600 MHz, QO-100, C band 5150 MHz (inverted), HF upconverter +125 MHz, or a custom oscillator. The type is RF - LO (down-converter), RF + LO (up-converter) or LO - RF (oscillator above, spectrum inverted).
• Sweep tab: set a range (low and high in MHz, step presets) and press Sweep a range. The explorer steps through it, builds a panorama and lists the signals it detects, each with frequency, -3 dB bandwidth, level and, for flat carriers, symbol rate. Stop sweep ends it. The result can be saved as a table.
• Bookmarks: star (*) a frequency, or a selected region as a named range; Export and Import the list.
• GRAVES: tunes 143.050 MHz, the French space radar, with a narrow window and the finest bins so the Doppler tracks of meteors and satellites show as short streaks.
• Range (selected region): restricts the sweep to the region you selected.

Troubleshooting

• Signals jump when I change gain. Overload; reduce the gain.
• I cannot zoom further. The finest bin width is set by RBW and the sample rate; choose a finer RBW or a lower sample rate.
• A signal is there but Identify gives no mode. Short bursts or a weak signal; select a longer or stronger part.
• Frequencies are off by the LNB offset. Set the Converter to your LNB preset; QO-100 has its own mode with beacon correction (see QO-100).
• The sweep is slow. Narrow the range or use a faster radio.

Tips

• Select a digital carrier tightly: the symbol-rate estimate works best on the flat top.
• Use bookmarks as your own frequency list for places you check often.

Legal and privacy notes

Looking at the spectrum is passive. Measuring your own transmitter is fine; what you decode from others is subject to local law.

Under the hood

The view is a Welch-averaged FFT with selectable resolution bandwidth. Region measurements find the peak, the -3 dB and -26 dB edges against the estimated noise floor, integrate the power, and use the flat-top width and the roll-off ratio to estimate symbol rate.

Related

Mode page: Spectrum explorer | Spectrum analyser | Signal workbench | DVB-S/S2 | QO-100 | Supported radios