Wiki Reference

Glossary

Short explanations of the terms that appear in the wiki and in the app window, with links to the pages where they are covered in detail. The terms are in alphabetical order. Terms of the paid SDR SA PRO app are marked PRO.

ACPR PRO: The ratio of the power in an adjacent channel to the power in the band itself. In SDR SA PRO the trace markers give it in the Adjacent below and Adjacent above lines: the power in a band of the same width right below and right above the band between two markers, in decibels relative to that band. Tuned mode only. See Trace markers.
Activity in a range PRO: A row of the SDR SA PRO Scanner list with an empty circle and the word "activity": not a signal but a range where detections appear again and again without becoming a signal row — a hopping frequency, rare bursts. Next to it the row says in how many of the latest looks this happened. See Scanner.
AGC: Automatic gain control: the device itself drives the gain, levels stop being comparable between frames, and the gain total is no longer known. The free edition has the RTL-SDR Tuner AGC; in SDR SA PRO PRO there is the device AGC of the Pluto and the bladeRF. The app's receiver audio has no AGC. See RTL-SDR, ADALM-Pluto, bladeRF.
Alarm PRO: In the SDR SA PRO Scanner, a signal that the rules of the frequency table point at: any signal in a watch range, a signal in a guard range that no narrower label row explains, or a signal whose type is in the Alarm on types list. The row turns red, and an ALARMS: … badge appears at the bottom of the window. Sound, the event log and IQ recording on an alarm (tuned mode only, no pre-trigger) are switched on separately, and all are off by default. A recording from a file and the demo signal give no alarms. See Scanner.
Auto scale: The mode in which the app drives both ends of the scale itself: the top follows the highest peak of all visible traces, the bottom follows the noise floor 0.9.25. A single spike does not move the axis. See Auto scale.
Band power PRO: In SDR SA PRO, the In the band line of the trace markers: the sum of the power of the cells between two markers divided by the noise bandwidth of the window (ENBW), so the number is true both for noise and for a tone. Tuned mode only and traces T1…T4 only. See Trace markers.
Bias tee: DC power fed through the antenna connector — for an external amplifier or an active antenna. Switch it on only with a load that expects it, not with an ordinary antenna. See HackRF One and RTL-SDR 0.9.25.
Bin: One cell of the FFT grid along frequency; its width is the sample rate divided by N. The RBW is wider than a bin by the factor of the window's ENBW. See ENBW.
bladeRF PRO: The bladeRF 2.0 micro by Nuand — an SDR SA PRO receiver 0.9.45. Receive only, one channel; tuner 70–6000 MHz, sample rate 0.52–61.44 MS/s, 12 bit. The app works with it through the maker's libbladeRF library. See bladeRF.
CA-, GO-, SO-, OS-CFAR PRO: Search methods of the SDR SA PRO Scanner 0.9.47 in which the floor for each bin comes from neighbouring cells on both sides (beyond guard cells). CA — the mean of the neighbours: it follows the local level, but a strong neighbour raises the floor and hides a weaker signal. GO — the greater of the two side means: no false detections on level steps, but a weak signal next to the edge of a strong one is lost. SO — the smaller of the two: more sensitive near edges, but showers false detections on steps. OS — an order statistic of the neighbours: a few strong neighbours do not raise the floor. See Scanner.
Capture: An entry in the SigMF metadata describing a stretch of the file recorded on one frequency. A frequency change during a recording opens a new capture 0.9.25. See IQ recording.
CFAR: Constant false alarm rate detection. In the app these are marks at the bottom of the spectrum where the level exceeds the local noise floor by more than noise itself does with a chosen probability. See Detection marks and the spur passport. The SDR SA PRO Scanner PRO has other variants too — see CA-, GO-, SO-, OS-CFAR.
CISPR: CISPR 16-1-1 is the standard for measuring receivers used in electromagnetic compatibility (EMC) work. The time constants of the qp, cav and crms detectors are taken from it; in the app they give a preliminary estimate, not a compliance measurement. See CISPR detectors.
Coverage: The share of air time the spectrum was really computed from. It is below 100 % when the machine cannot keep up and the spectrum is computed from fewer than all blocks; the number then stands in the trust bar. See Spectrum frames and Spectrum from blocks.
CTCSS: The sub-audible code of an analogue radio: a tone of 67–254 Hz transmitted together with the voice. The app recognises the tone and shows by how many decibels it stands above the neighbouring tones of the table. See Receiver.
dBFS: Decibels relative to the full scale of the ADC: a full-scale tone reads 0 dBFS. Levels from HackRF One, RTL-SDR, recordings and the demo signal are shown in these units, and in SDR SA PRO also from Pluto, Fobos SDR and bladeRF; this is not calibrated power at the input. For the scale it is counted from, see Full scale. See dBFS, dBm and the UNCAL badge.
dBm: Decibels relative to one milliwatt — calibrated power. In the app only a tinySA gives dBm, because it measures by itself 0.9.25. There is no calibration of IQ-receiver levels in dBm in either the free edition or SDR SA PRO. See tinySA and tinySA Ultra.
DC spike: The peak exactly at the centre of the captured band: local-oscillator leakage and the receiver's DC component, not a signal on the air. On the plot it carries the DC mark; the DC filter removes it from the stream.
Demo signal: The built-in source that needs no hardware: a demonstration signal with known levels. See Demo signal and IQ files.
Detector: The rule by which several spectra (or bins) are reduced to one point on the screen: maximum, mean power, median and so on. The app has eleven detectors, and every trace has its own. See Detectors.
Drops: Samples lost on the way from the device to the app. The Drops counter stands in the trust bar; overall, losses are counted separately on four levels — source ring, USB transport, pause, writer ring. See Trust bar and loss counters.
Duty cycle: The fraction of the period occupied by a pulse: duration divided by period. In the app it is the Duty cycle field of the zero-span measurements. See Zero span and trigger.
ENBW: The equivalent noise bandwidth of a window in bins: one spectrum sample "weighs" that many bins of noise. From 1.0 for the rectangular window to 5.65 for HFT248D; it is what makes the RBW differ from the grid step. See ENBW.
Event log PRO: A CSV file of the SDR SA PRO Scanner: a row per alarm — time (UTC), frequency, width, level, reason, the name and type of the range, whether it is a signal or activity, the alarm number and the channel number. It is written only while it is switched on, into the scanner\ folder of the app's data folder: a file per day (UTC), no more than 1000 rows a day, and the last 30 days are kept. See Scanner.
Fobos SDR PRO: A receiver by RigExpert that SDR SA PRO works with 0.9.43: receive only, tuner 50–6900 MHz. The app opens it through the maker's libraries and recognises the firmware by itself; with the maker's special firmware 0.9.44 the sweep runs as the device's own scan. The LNA and VGA controls are step numbers, not decibels. See Fobos SDR.
Fold: How many spectra the detector has reduced into one waterfall row; in the trust bar it stands next to the detector name, for example rms ×11. The fold determines how the detector shifts the noise level. See Bias on noise.
FPGA image PRO: The configuration of the programmable logic of a bladeRF. The maker's images for the three bladeRF 2.0 micro chips (xA4, xA5, xA9) ship with the app, and SDR SA PRO loads one by itself into a device that has no image in its flash memory. See bladeRF.
FPV-video: The receiver mode for analogue FM video from FPV cameras: the picture is shown in a window of its own, without audio. See FPV video.
Frequency table PRO: The second list of the SDR SA PRO Scanner tab: frequency ranges with a name, a type, an expected width, a role and a priority. A signal in a range gets its name and type; a range can be divided into channels of one width; the role of a range — label, watch or guard — sets the alarms. Exchange is through CSV files. See Frequency table.
Full scale: The largest value the ADC can give; dBFS is counted from it. In recordings from the SDR SA PRO receivers it is smaller than the scale of the sample type (12 bit in ci16_le, float32 with a scale of ±0.25 in cf32_le), and the SigMF sidecar names it in the sdrsa:full_scale field. See IQ recording.
Heat map: A trail behind the spectrum curve whose colour shows what share of time the curve spent at that level: a carrier is hot, noise and isolated bursts are cold. It is switched on with a right-click on the spectrum. See The heat map.
Hysteresis (two thresholds) PRO: The SDR SA PRO Scanner search method Two thresholds (hysteresis): the upper threshold is statistical, while the edges of a stretch follow the lower one, a set number of decibels lower. A signal does not crumble into pieces, and noise that exceeds only the lower threshold is not taken. See Scanner.
Instantaneous bandwidth: The band the receiver sees at once; it equals the sample rate — up to 20 MHz on a HackRF One and up to 2.56 MHz on an RTL-SDR. A wider span is shown by a sweep. See Sweep.
IQ: The stream of complex samples (the in-phase component I and the quadrature component Q) that the receiver delivers to the app. The spectrum, the audio and zero span are computed from it; it is also what is written to a file during a recording. See IQ recording and Demo signal and IQ files.
LNA, VGA, AMP: The three gain stages of a HackRF One. LNA (RF) is the gain before the mixer: this is where gain is added first and also where it is reduced on overload. VGA (IF) is the intermediate-frequency gain: it only stretches what is already there, noise included. AMP is the input amplifier before the filters, easily overloaded in a city. The defaults are LNA 32 and VGA 36 0.9.25. See HackRF One. In SDR SA PRO PRO a Fobos SDR has LNA and VGA controls too — as step numbers, not decibels (see Fobos SDR).
Local oscillator (LO): The receiver's oscillator that sets the tuned frequency. On a HackRF One its frequency is the centre of the captured band, and that is exactly where the DC spike sits. Spurs born inside the receiver move together with the local oscillator — this is how the app tells them from the air. See Sweep.
MAD PRO: Median absolute deviation — a measure of spread that resists outliers. In the SDR SA PRO Scanner the Median + spread (MAD), dB method puts the threshold at the median plus k spreads in decibels, by blocks. It does not rely on the noise distribution, so it suits air with impulsive interference. See Scanner.
Marker (trace marker) PRO: In SDR SA PRO, a diamond on a trace that reads the level of the cell it stands on, in the units of the level axis. There are six markers; to place one, right-click the spectrum → Marker here, or press To peak. A level that the trace does not hold right now is not shown, and the marker says why. The free edition has no markers. See Trace markers.
Max hold and Min hold: Trace modes: the highest and the lowest value the trace has seen at every point. Max hold keeps a short burst on screen, but it also collects every noise spike, so it is not a noise level. See trace modes.
MSIX: The Windows package format in which the app is installed from Microsoft Store. In the installed package the settings live in the Documents\SDR Signal Analyzer folder; in the portable build (ZIP), next to the program. SDR SA PRO has its own folder — Documents\SDR SA PRO. See Settings, files and language.
N (FFT size): The number of samples in one FFT frame and at the same time the number of bins in the spectrum: the list offers powers of two from 256 to 16384. In the app N follows from the requested RBW rather than being the primary parameter. See N — the FFT size.
Noise density PRO: The noise power per hertz of bandwidth. In SDR SA PRO, the Noise density line of the trace markers: the mean over five cells around the selected marker divided by the noise bandwidth of a bin, in dBFS/Hz. It makes sense where there is noise under the marker, not a signal. See Trace markers.
Noise floor: The level at which the receiver's noise lies between signals. The Pedestal field shows it as the 5th percentile of the live spectrum; the floor detector draws the local floor as a separate trace. See floor.
OBW PRO: Occupied bandwidth — the band that holds a given share of the power. In SDR SA PRO it is the Occupied, … % line of the trace markers: the share is taken of the power of the range between two markers (99 % by default, from 50 to 99 %), and the rest is cut equally from both edges. The noise of the range counts in the power just like the signal. Tuned mode only. See Trace markers.
Occupancy PRO: The percentage in a row of the SDR SA PRO frequency table: the share of looks with at least one detection in the range. This also shows rare bursts that the signal list does not hold. See Frequency table.
OpenGL: The graphics-card interface used to draw the spectrum and the waterfall. Version 3.3 is required: without it the rest of the app works, but there is no picture, and the app explains why. See Troubleshooting.
Palette: The colour scale of the waterfall and the heat map. Of the five palettes two — gqrx and turbo — are not monotonic in lightness: level cannot be read by eye in them. See Palettes and gamma.
Passport (self-spur passport): A list of the frequencies at which the receiver itself generates spurs; it is taken in a sweep with no antenna. Those bins are marked as the device's own rather than the air, and can be cut out of the measurement on request. See Detection marks and the spur passport.
Peak search PRO: In SDR SA PRO the To peak button puts a trace marker on the highest point of what is visible, Next on the highest peak below the level under the marker; there are also buttons for the nearest peak on the left and on the right. A peak is a top from which the trace falls on both sides by at least the Peak excursion, dB (6 dB by default); it is searched for among what is visible. See Trace markers.
Pfa: The per-bin probability of false alarm for the CFAR marks: 10⁻⁴ or 10⁻⁶. The actual rate is higher than the chosen one — twice in tuned mode and several times in a sweep — and the app says so. See Detection marks and the spur passport.
PLL: The frequency synthesiser of the RTL-SDR tuner 0.9.25. If it has not locked, the frequency under the spectrum is unreliable, and the trust bar carries the red PLL NOT LOCKED badge. See RTL-SDR.
Pluto PRO: The ADALM-Pluto and Pluto+ by Analog Devices (AD9361 / AD9363 chip) — the first SDR SA PRO receiver. The link runs over the device's own network: over USB this is its own network interface, and a Pluto+ also has Ethernet. Receive only, one channel. Over USB it is loss-free only up to ~5 MS/s, and only on an idle machine. See ADALM-Pluto.
ppm: Parts per million. In the app this is the correction for the crystal error of an RTL-SDR dongle 0.9.25: 30 ppm at 100 MHz is a 3 kHz offset. The value is kept for the next launches. See RTL-SDR.
PRO key: What switches on the PRO features in SDR SA PRO. The key window appears at start-up when there is no valid key. The Help → License window shows the key state, what the key enables and the code of this computer needed to order one; the key window to enter a new key opens from there too. A key entered that way while the app is running enables the PRO receivers at once, and the Scanner tab and the trace markers from the next launch of the app. Without a valid key the app works as the free edition. Price and terms on request. See SDR SA PRO.
Quasi-peak: The qp detector per CISPR 16-1-1, with charge, discharge and meter time constants: it weights impulsive interference by its repetition rate. In the app it is a preliminary estimate, because the RBW is not the one the standard requires. See CISPR detectors.
RBW: Resolution bandwidth: the width of the band one spectrum point "sees". A narrower RBW resolves closer signals and lowers the noise floor, but needs a longer frame. It is set in hertz. See RBW: requested and achieved.
Ref: The reference level — the top of the level scale and of the waterfall palette. Not to be confused with the reference trace R. See the Amplitude group.
Reference trace: Trace R — a snapshot of one of the traces T1…T4 that does not update. It is used to compare "before and after" and as the second operand in trace math. See The reference trace R.
Sample rate: How many complex samples per second the receiver delivers, in MS/s. This is the instantaneous receive bandwidth: 2–20 MS/s on a HackRF One, 1.024–2.56 MS/s on an RTL-SDR. In SDR SA PRO PRO — within the limits the device itself names: Pluto 2.5–30.72 MS/s (on the tested device), Fobos SDR 8–80 MS/s, bladeRF 0.52–61.44 MS/s. See HackRF One and RTL-SDR.
Scalloping: The low reading of a tone that falls between two bins: up to 3.92 dB with the RECT window, up to 1.42 dB with HANN, up to 0.01 dB with FLATTOP. In the free edition only the choice of window reduces it; in SDR SA PRO PRO a marker on the top of a tone also shows the level refined between bins. See The seven windows.
Scanner PRO: An SDR SA PRO tab that looks for signals in a sweep and in tuned mode and keeps a list of them: centre, width, level in dB above the local noise floor (not dBm), how many times the signal was seen out of how many looks. The search method can be chosen 0.9.47; the default is Statistical (from the noise distribution). Without a valid key the tab is absent. See Scanner.
SDR SA PRO: A separate paid app, installed next to the free one, with its own settings folder. It does everything the free one does, and on top of that has the Pluto, Fobos SDR and bladeRF receivers, the Scanner tab and trace markers. The PRO features are switched on by a key; without a valid key the app works as the free edition, and the PRO receivers, the Scanner tab and the trace markers are unavailable. Price and terms on request. See SDR SA PRO.
Segment and seam: A segment is the stretch the receiver captures in one retune during a sweep (the app's messages call it a "tune"). A seam is the junction of neighbouring segments: in the overlap zone the app passes smoothly from one to the other. See Sweep.
SigMF: An open metadata format for IQ recordings: next to the sample file lies a description file with the frequency, the sample rate, the format and the marked gaps. The app updates it during the recording, so even a killed process leaves a readable file. In its own sdrsa:… fields it also gives the losses, the full scale and the transport breaks. See IQ recording.
Spectral kurtosis: A statistic that tells from the scatter of level in a bin what is in it — noise, a steady signal or an intermittent one — without knowing the noise level. In the app these are the green and red class marks; it works in tuned mode only. See Detection marks and the spur passport.
Spur: A spurious signal generated by the receiver itself rather than the air. Some spurs move together with the local oscillator — the app catches them with a pass on a shifted local oscillator; others sit at fixed frequencies — the passport is for those. See Detection marks and the spur passport.
Squelch: A gate that mutes the audio while the level in the channel is below a threshold. The threshold (Squelch level) is measured in the channel after the filter, not across the whole band, so a strong neighbour does not open the squelch on an empty frequency. See Receiver.
Sweep: The mode in which the receiver retunes quickly through segments and the app stitches them into one spectrum wider than the instantaneous bandwidth. It starts by itself when the selected span is wider than the device's widest sample rate. See Sweep.
Trace: A spectrum curve with its own accumulation mode (Live, Max hold, Min hold, Average) and its own detector. There are four traces, T1…T4, plus the reference R. See Traces.
Trust bar: The row that is always on screen and says under which settings and with which losses the picture was obtained: RBW, VBW, N, the window with its ENBW, the detector with its fold, averaging, coverage, drops and the badges. See Trust bar and loss counters.
Tuned mode: The ordinary mode in which the receiver stays on one frequency and the screen shows its instantaneous bandwidth. The overview ruler then carries the tuned mark. The opposite is a sweep. See Sweep.
UNCAL: "Uncalibrated". The dBFS — UNCAL badge in the trust bar is a reminder that levels from IQ receivers are not calibrated power. See dBFS, dBm and the UNCAL badge.
VBW: The video filter: it smooths the trace in time after the detector, without narrowing the RBW. From 0.5 to 30 Hz, or off; a burst shorter than the filter's time constant reads low. See VBW — the video filter.
VFO: The receive band drawn on the spectrum: the frequency, the demodulation mode and the filter width that the audio works with; zero span takes its envelope at the same frequency. It is set in the Frequency group. See Receiver.
Waterfall: The history of the spectrum: every row is the spectrum over a short interval of time, the colour is the level. See The waterfall.
Window: The weighting function a frame of samples is multiplied by before the FFT. It trades level accuracy for resolution; the app has seven windows, HANN being the default. See The seven windows.
WinUSB: A USB driver built into Windows. It is assigned once to a HackRF One or an RTL-SDR with the Zadig utility; the app itself installs no drivers. A tinySA does not need it — it is a serial port. In SDR SA PRO PRO a Fobos SDR needs WinUSB through Zadig too; a bladeRF works with the driver from the Nuand installer or with WinUSB through Zadig, and a Pluto over USB needs the driver from Analog Devices. See Getting started.
Zadig: A third-party utility used to assign the WinUSB driver to a device: zadig.akeo.ie. It is not affiliated with the app and is not part of it. See Getting started.
Zero span: The mode in which the receiver stays on one frequency and the plot shows the level at the VFO frequency over time — in the band of zero span's own filter (RBW). With a trigger it measures the duration, period and duty cycle of pulses. See Zero span and trigger.

The wiki describes version 0.9.49. Your app's version is shown in the Help menu, under About. Found a mistake? Write to us.