SDR Lab: receive, measure, understand
SDR lab for radio amateurs and listeners: convert dBm, microvolts and S-units, calculate dynamic range, bandwidth and resolution of your SDR receiver, correct the frequency in PPM and choose the right receiver and software for what you want to hear.
For antennas and SWR go to Antennas & Measurements; for noise and interference to QRM Troubleshooting. Antennas & Measurements → · QRM Troubleshooting →
SDR lab calculators
Theoretical values to understand your receiver’s numbers. Real receivers perform below the ideal: use the results to compare and understand, not as certified measurements.
S-meter: dBm, microvolts and S-units
Converts a signal level between the three units, in 50 Ω.
Formula: dBm = 20 log(µV) − 107; S = 9 + (dBm − S9) / 6
Ideal ADC dynamic range
How much signal “fits” above the quantisation noise.
Formula: S/N = 6.02 N + 1.76 dB + 10 log(fs / 2B)
Sampling and FFT resolution
How much bandwidth you see and how fine the spectrum is.
Formula: bandwidth = fs; resolution = fs / N; duration = N / fs
Frequency correction (PPM)
How far off your SDR’s oscillator is.
Formula: PPM = (f shown − f known) / f known × 10⁶
Which SDR receiver for what
The main families, with one example each. Data as published by the manufacturer or the distributor shown.
Low-cost 8-bit
To get started, VHF/UHF, ADS-B, weather satellites, basic HF listening.
Example: RTL-SDR Blog V4: 0.5–1766 MHz, 8-bit ADC, stable up to about 2.56 MHz bandwidth, 1 ppm TCXO, 4.5 V bias tee.
WiMo — RTL-SDR V4 (specifications) ↗
RTL-SDR Blog — V4 users guide ↗
12–14 bit, wide coverage
More dynamic range: HF with strong nearby signals, serious listening from longwave to low microwave.
Example: SDRplay RSP1B: 1 kHz–2 GHz, 14-bit ADC, up to 10 MHz of spectrum.
HF specialist
HF and medium-wave reception with strong overload resistance; narrow but clean bandwidth.
Example: Airspy HF+ Discovery: 0.5 kHz–31 MHz and 64–260 MHz, usable bandwidth up to 660 kHz.
Experimental SDR transceiver
Experimenting over a wide range, including transmit: a licence and external filters are required.
Example: HackRF One: 1 MHz–6 GHz, 8-bit samples, up to 20 million samples per second, half-duplex.
SDR software
The most used programs, with the operating systems stated on the official website.
SDR++
Windows, Linux, macOS, BSD · open source. Light and modern; the list of supported receivers is on the official website.
SDR# (SDRSharp)
Windows. Drivers for Airspy, RTL-SDR, HackRF and others; very popular for listening.
SDRconnect
SDRplay’s current software for its receivers: Windows x64, macOS, Linux (Ubuntu LTS). SDRuno has been declared end-of-life by the manufacturer.
Gqrx
Linux and macOS. Supports Airspy, Funcube, RTL-SDR, HackRF and USRP.
SDRangel
Open-source program for receive and transmit with many demodulators; platforms and versions on the project page.
Practical guide
The rules that make the difference between an SDR that “hears everything and nothing” and one that receives well.
The right gain
Connect the antenna and raise the gain until the noise floor rises a few dB above the level with the antenna disconnected: beyond that you gain no signal, only overload.
Recognising overload
Signals in odd places, “mirrors” of strong stations, the whole floor rising together: lower the gain or add a filter.
Filters
An FM broadcast 88–108 MHz notch almost always rescues low-cost SDRs; on HF a low-pass or band-pass filter removes strong out-of-band signals.
Antenna and cables
Antenna outdoors and away from the computer; good coaxial cable; a USB extension with ferrites to keep the receiver away from PC noise.
Frequency stability
Let the receiver warm up and correct the PPM with the calculator; models with a TCXO drift much less.
Common problems
The most frequent cases with an SDR receiver and how to fix them.
Fixed spike in the centre of the spectrum
Many direct-conversion SDRs show a spike at the centre frequency: tune the signal slightly to one side or use the software’s offset option.
Stations appearing where they should not
Usually overload (gain too high or strong nearby signals) or an image frequency. Lower the gain and try a filter.
Lots of comb-like or regular noise lines
Often from the computer, the power supply or the USB cable. Try another power supply and a USB extension with ferrites. More in QRM Troubleshooting. QRM Troubleshooting →
The signal drifts while you listen
Oscillator thermal drift: wait for the receiver to warm up and correct the PPM.
The receiver is not recognised
Missing or wrong driver: use the one indicated by the manufacturer (the RTL-SDR V4 needs updated drivers) and a direct USB port.
Sources: IARU Region 1 Technical Recommendation R.1 — S-meter (archived copy), Wikipedia — S meter, Analog Devices MT-001 — SNR = 6.02N + 1.76 dB, WiMo — RTL-SDR V4 (specifications), RTL-SDR Blog — V4 users guide, SDRplay — RSP1B datasheet, Airspy — HF+ Discovery, Great Scott Gadgets — HackRF One, SDR++, Airspy — SDR# download, SDRplay — SDRconnect, SDRplay — SDRuno, Gqrx SDR, SDRangel (GitHub). Sources consulted on 18 October 2026. Links open on the publisher’s website. RadioMeteo does not sell receivers and receives no payment for the models mentioned.
Articles on SDR and radio listening
RadioMeteo articles on SDR receivers, WebSDR and software appear here automatically when they are published.
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