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Trace markers and power measurements

PRO Trace markers are six markers M1…M6 on the spectrum. A marker reads the level of a trace where it stands, looks for peaks, shows the frequency and level difference between two markers and puts the receiver on its frequency. For the selected marker the app computes the noise density, and between two markers the band power, the occupied bandwidth (OBW) and the adjacent channels (ACPR). A number that the trace does not hold right now is not shown — the marker says why.

Where the markers are

• The Spectrum analyzer tab, the Trace markers group — below the Markers group (which stays in its place with the VFO, the bandwidth and the visible span). The “?” circle before the heading briefly explains how to place a marker and what a peak is.
• On the spectrum each marker that is on is a diamond at its frequency and level, labelled M1…M6.
• Markers exist only with a valid SDR SA PRO key. A key entered in the window at start-up takes effect at once; one entered later from the Help menu — from the next start of the program. See What SDR SA PRO is.

How to place a marker

Right click on the spectrum → Marker here

Places a marker at the frequency where you clicked. The first marker that is off is taken; when all six are on, the selected one moves. The new marker reads the same trace as the selected one (if the selected one is on), otherwise T1, and becomes the selected one itself.

To peak

Moves the selected marker to the highest point in view on its trace; a marker that is off is switched on. From the start the selected marker is M1, so this button pressed first switches M1 on.

While there are no markers, the group says: No markers. Right-click the spectrum → “Marker here”, or press “To peak”. A marker cannot be dragged with the mouse. Markers are not saved between runs.

A marker row

The group shows rows only for markers that are on. A row holds:

• the M1 · T1 button — the marker number and the trace it reads; a click makes the marker selected (its button is highlighted). The action buttons and the lists below act on the selected marker;
• the frequency in megahertz to the hertz, for example 2255.000000 MHz, and below it the level, for example −52.31 dBFS, or a dash when there is no level;
• the × button — Switch the marker off.

Below the row, when needed, come a few more lines:

• no level: … — why there is no number (see below);
• a yellow caution about unmeasured places in the trace (see below);
• tone between bins: … — the frequency and level of a tone (see below);
• Δ from M2: … — the difference from another marker (see below).

The rows re-read the trace several times a second: what the trace shows now is what the marker says.

A marker on the spectrum

• The diamond stands at the marker’s frequency and level; the selected marker is filled with the accent colour, the others are only outlined.
• A level beyond the scale is pressed to the edge of the field; the number itself is in the group.
• A marker without a level has no diamond: at its frequency there is a faint vertical line and a label with “—”.
• A marker with a difference is labelled, for example, M2Δ1.
• The diamond travels with the spectrum when the view is dragged or zoomed.

What a marker reads

A marker reads the trace cell it stands on — what the trace shows — in the units of the level axis. The frequency in the row is the centre of that cell; when there is no level, it is the frequency where the marker was placed.

• In tuned mode a cell is an FFT bin. In a sweep it is a group of bins reduced into one cell, and the level there is what the reducing detector gave, not a single bin.
• The unit is the one on the level axis: dBFS (uncalibrated) with IQ receivers, dBm with a tinySA — its own calibrated levels (see tinySA and tinySA Ultra). On a tinySA the marker frequency is the one at which the instrument measured 0.9.41.
• A marker holds an absolute frequency. Retune the receiver and the marker stays where it was; if the new band does not cover it, it has no level.
• The trace for a marker is set by the Trace list: T1…T4 or Ref (the reference trace, see Traces).

Peak search

A peak is a top from which the trace falls on both sides by at least the peak excursion before rising above it. The fall is counted only over measured cells: the edge of the trace and a hole in it prove no fall, so a maximum near the edge with a cut-off slope is not a peak. The search always runs over what is visible on the trace of the selected marker.

To peak

To the highest measured point in view. This button needs no excursion: it is simply the largest cell.

Next

To the highest peak below the level under the marker. The same peak is not taken twice.

◄ and ►

To the nearest peak on the left and on the right.

Peak excursion, dB

How far the trace must fall on both sides of a top: from 1 to 40 dB, default 6.

For a marker that is off, Next, ◄ and ► act as To peak. When a button did nothing, a yellow line below the Peak excursion, dB field says why, for example:

• No lower peaks in view (excursion 6 dB)., No peaks to the right in view (excursion 6 dB).;
• The marker is out of view — put it on a peak first.;
• Nothing is measured on the trace in what is visible.;
• There is no trace T1 now — nowhere to look for a peak.;
• Trace T1 was taken at another tuning — its levels are not about these frequencies, and no peaks are looked for on it.;
• Trace T1 has unmeasured places filled with a floor: a fall to them proves no peak, and neighbouring peaks are not looked for on such a trace. — for Next, ◄ and ► on a tuned-mode trace from which spurs have been cut.

The peak search has no threshold above the floor: on a trace that is not averaged, Next also steps onto noise spikes.

Difference between markers

The Δ from list picks for the selected marker another marker (M1…M6) or — — no difference. There is no difference from the marker itself.

• The line Δ from M1: +1.234 kHz, −3.10 dB is the difference of the cells’ frequencies and levels: this marker minus the reference one.
• If both markers have a tone between bins, by tones: … is added — the difference of the refined frequencies and levels.
• If that marker is off or one of the two has no level — Δ from M1: — (that marker is off, or one of the two has no level).
• A marker placed in a freed slot does not inherit other markers’ “Δ from”: a difference that was counted from the old marker of that number is reset.
• The pair “a marker and its Δ from” also sets the band for the power measurements.

Receiver to the marker

Receiver → to marker

Centres the receiver on the selected marker (the captured band is as wide as the current sample rate). In a sweep this stops the sweep. The marker itself stays at its frequency. The button is inactive when the source cannot be retuned; if tuning failed, a yellow line says Tuning failed: … with the reason.

All off

Switches all six markers off and resets their differences.

Tone between bins

The raw top of a tone that sits between two bins is lowered by the scalloping of the window — by up to 1.42 dB for the default Hann window (the table is on the page RBW, windows and VBW). On a tone top the marker shows a second line, tone between bins: … — the frequency and level of the tone refined by the window response. Both numbers carry their own names: the marker row is the cell, the second line is the tone.

The refinement happens only when all of this is true:

• tuned mode, and the trace cell is an FFT bin with a known window (not a sweep, not a trace with math);
• the trace is T1…T4, not the reference: the reference does not carry which window it was taken with;
• the window is not rectangular (RECT): with it and the peak detector the refinement raised the level by up to 4 dB in a test, so with this window it is not done at all;
• the cell is a top, not lower than its neighbours;
• the top stands at least 15 dB above the local noise around it, and the cells on its slope lie where the window puts them.

A weaker tone (less than 15 dB above the noise) keeps the level of the cell.

When there is no level

A level that the trace does not hold right now is not shown: there is a dash instead of the number, and below the row — no level: … with the reason.

there is no trace T1 now

The trace is off or hidden, has not arrived yet, or vanished when the band changed.

outside the band

The marker frequency lies beyond the trace — for example, after a retune.

not measured here

Nothing has been measured in the cell: an empty Max hold before the first pass, A−B where A<B.

the trace was taken at another tuning — its levels are not about these frequencies

A frozen or reference trace has outlived a retune of the receiver: it stays on screen but was taken at other frequencies, and the marker does not read it.

Unmeasured places filled with a floor

A trace can have places where nothing was measured but the app filled them with a floor: spurs cut out in tuned mode, and in a sweep — places the pass has not reached yet or skipped. A marker does not tell such a cell from a measured one: it shows the number, and a yellow line warns that the trace has unmeasured places.

• the trace has unmeasured places filled with a floor — the program does not say where — in tuned mode;
• sweep: the cell under the marker may be unmeasured, filled with a floor — in a sweep; there this caution is shown almost always.

On a tuned-mode trace with cut-outs, Next, ◄ and ► do not search. In a sweep they do, but false peaks occur among those found: the fall that makes a top a peak may be a filled place, and such a top does not necessarily stand next to it.

Power measurements

Below the markers are the measurements for the selected marker. The heading says what they are computed over: Power on trace T4, marker M1 or, when the marker has Δ from another marker that is on, Power on trace T4, band M1–M2. The band runs between the frequencies of the two markers; the trace is that of the selected marker.

Noise density

The power density under the selected marker, in axis units per hertz (dBFS/Hz): the mean power of five cells around the marker divided by the noise bandwidth of a bin. Near the edge of the trace there are fewer neighbours — as many as there are are taken. It makes sense where there is noise under the marker, not a signal.

Band width

The distance between the frequencies of the two markers.

In the band

The sum of the power of the cells between the two markers (an edge cell by its share), divided by the noise bandwidth of the window (ENBW). That makes the number true for noise and for a tone alike, wherever the tone sits between bins.

Occupied, N %

The occupied bandwidth (OBW): the width of the band that holds the set share of the power between the markers; the rest is cut equally from both edges. Below it are the edges of that band. The noise of the stretch counts as power, just like the signal: a stretch much wider than the signal gives a band wider than the signal. The line is there only when the occupied band has been computed.

Share for the occupied band, %

From 50 to 99, default 99.

Adjacent below and Adjacent above

The power in a band of the same width right below and above the band between the markers — in dB relative to the power in the band itself (ACPR). Adjacent channels are only of this kind: the same width and contiguous. When an adjacent channel cannot be computed, no adjacent channel: … is shown. Both lines are there only when In the band has a number.

Everything is computed in linear power: cell levels are converted to power, summed, and only the sum goes back to decibels.

When there is no number

A dash replaces the number, and a yellow line names the first reason:

• a cell of the trace is not an FFT bin (sweep, reduced trace, power device, trace with math or the reference): its noise bandwidth is unknown;
• part of the band is not measured;
• the band goes beyond the trace;
• the band has zero width;
• the trace has unmeasured places filled with a floor — the program does not say where;
• the trace was taken at another tuning — its levels are not about these frequencies;
• there is no trace T1 now.

Caution: the trace is not mean power

A trace carries mean power only with the rms or sample detector and with averaging in power. When that is not so, the number is there, but it is not what it seems — and below the measurements stands Caution: …:

• a Max hold trace is not mean power (likewise Min hold);
• the trace detector is peak: mean power of noise and modulated signals comes from RMS — for any detector other than rms and sample (see Detectors);
• averaging type is Log: an averaged trace and VBW read noise up to 2.51 dB low — when the Averaging switch is set to Log (video) (see Averaging).

The default T1 (peak, Live) gets this caution; the default T4 (Average, rms) with Power averaging does not. The default trace settings are on the page Traces.

Limits

• Levels with IQ receivers are dBFS, uncalibrated; dBm only with a tinySA. This version has no calibration in dBm for IQ receivers.
• Power measurements work only in tuned mode and only on T1…T4; the tone between bins is likewise tuned mode only.
• A marker does not tell unmeasured places filled with a floor from measured ones — it only warns that the trace has such places.
• On a trace with math the marker number is a ratio in dB, yet it is labelled with the unit of the level axis.
• At the edge of a wide flat signal with the sample detector the outermost top is occasionally called a tone; the level then differs from the cell by no more than the window’s scalloping.
• A marker cannot be dragged with the mouse; markers, the peak excursion and the share for the occupied band are not saved between runs.
• There is no peak table.

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.