spectrum.md

neumoDVB

Spectrum scan

Spectra are always scanned using a specific LNB. Make sure tat this LNB is not in use for any other purpose, switch to the LNB list using Lists - LNBs, select one of the LNBs and press Ctrl-U to show the spectrum scan screen.

Spectrum scan only works if you have installed the Neumo blindscan drivers, and even then only on supported cards. You start by scanning a spectrum, which will then display a graph on the top part of the screen. Afterwards you can blind scan some or all of the found spectral speaks. Spectra are automatically remembered, which allows you to find changes.

The screenshot below shows an example of what you get during scanning 30.0W. This is a very complex screen, so the text below explains the various steps involved in spectrum acquisition and blind scan and provides some details on the related parts of the screen.

Blindscanning proceeds in two steps: first you need to acquire a spectrum. After that you can scan each spectral peak individually, or you can use Blindscan all. In the latter case, neumoDVB will scan all discovered spectral peaks. neumoDVB implements parallel blindscan on some cards, like those based on the stid135 chip. In this case all available frontends will be connected in parallel to the LNB being scanned. In practice this means that up to 8 (tbs6909x) muxes will be scanned simultaneously. Those muxes all will be in the same satellite band and from the same polarisation. Parallel scan is activated automatically.

Starting a spectrum acquisition

• At the very bottom left on the screen, first select the polarizations you want to scan. Also select the frequency range to scan. The default is to scan all, which will take about 40 seconds on TBS6909X.

• Then press the spectrum scan button.

Note that some cards, such as tbs5927 allow tuning outside of the normal frequency ranges. If the driver supports it, you can therefore also enter a low frequency limit the scan below 10.7 GHz or a high frequency above 12.75 GHz. However, this only works if the LNB frequency limits have been properly adjusted on the lnb list screen.

Spectrum scan is performed one band/polarization at a time. The result will be displayed as a graph on the top half of the screen. To prevent a complete mess, the graph - which, for a universal LNB, covers the range 10.7-12.75 GHz - is zoomed horizontally by default. Above the graph (top left) some command buttons are available to zoom and pan in the graph. These are from the matplotlib library and some of them may operate a bit awkwardly. From left to right

• The home icon will reset the graph to what it was at the start.

• The two arrow buttons allow you to undo and redo zoom/pan operations made using the other buttons.

• The cross button: while depressed, allows to pan vertically as well as horizontally by clicking the left mouse button and then dragging the cursor. Horizontal panning is (unfortunately) not coupled with the horizontal scroll bar below and can produce confusing results. Vertical panning is useful when some information is not on the screen. NeumoDVB tries its best to provide a good default layout, but does not always succeed.

  By clicking the right mouse button instead of the left one, and then dragging the cursor, you can also adjust the vertical and horizontal zoom factor.

  Important This pan mode remains in effect until you deselect the cross icon (by clicking on it)

• The loop icon provides another way of zooming, by selecting a rectangle. Again: do not forget to deactivate it after use.

• The equalizer button is of little use and will be removed at some point

• The floppy icon allows saving the currently displayed part of the plot as a picture.

To the right of these matlplotlib buttons are other buttons:

• The minus button turns on or off baseline removal. If you LNB is connected with a long cable, then signal drop a lot towards the end of the frequency bands. They are lowest just below 11.7 GHz and near 12.7 GHz. Base line removal subtracts this trend and allows a better view on the spectrum

• The other buttons allow you to turn on/off textual annotations on the displayed graphs, or to remove the displayed graphs, by clicking in the X.

At the bottom right of the screen, your will see a list under the heading Show/Hide spectra. This list contains the spectra you captured earlier and will of course initially be empty. Pressing Ctrl-Enter on any of the spectra, will add it as an additional graph in the plot, or remove it if it was already there.

So what exactly is in these plots? neumoDVB detects peaks in the spectrum, and estimates their center frequencies and bandwidths. From the bandwidths, neumoDVB estimates the symbol rate of the corresponding mux. This estimate is very rough and is derived from the width of the spectral peaks and does not take into account the specific modulation of the mux, which is not known at this stage. In fact, it is not even known that a discovered peak is actually a real mux.

This information is shown using vertical and horizontal lines. For narrow band transponders, these annotations could quickly become a confusing and overlapping mess. neumoDVB tries to prevent this by shifting text up as needed. Sometimes this may lead to to the text being above the visible part of the plot. Use the panning facilities in this case.

After blindscanning a mux (see below), the frequency and symbol rate of a peak is updated with the information received from the demodulator and -- when available -- with the values reported in the DVB service information of the mux. The latter always takes precedence. It is usually more accurate, but sometimes it is also completely wrong due to an error by the broadcaster. Really large errors are ignored by neumoDVB, but smaller ones cannot be detected and are not corrected.

The color of the text on a peak reflects the scan status: green if a the mux was successfully locked and scanned, red if no lock was achieved and black in all other cases. Only the green values are reliable.

Blind scanning muxes

After a spectrum has been acquired, press the Blindscan All button at the bottom to start blindscanning all peaks. neumoDVB will attempt to tune each of the found spectral peaks one after the other and try to lock a signal.

The whole process is similar to the manual approach that we describe below, except that neumoDVB automatically starts scanning the next peak after the current one is finished, In manual mode, You will need to manually start scanning the next peak.

Blindscan muxes

Scanning in manual mode works as follows.

• First disable Blindscan All if it is still in progress, by pressing the button.

• Select any of the peaks in the graph by clicking on the text or on the horizontal or vertical lines. The selected peak will turn blue (that is to say: its text will turn blue). It is not possible to select peaks which were not detected by the drivers, but you can still scan such peaks using text entry (see below).

• If, for some reason, the desired mux was not detected during peak scanning press Ctrl-A to enable mux drawing: first make sure that none of the matplotlib zoom/pan/scroll functions are active. Now click and drag anywhere on the spectrum plot and adjust the rectangle to cover the bandwidth of the desired mux. You can also press the H, V, L, R keys to indicate the desired polarisation. Once satisfied, press Enter. This will copy the selected values to the mux tune panel, where you can then tune the mux, possibly after changing some other values. During mux drawing, you can also press the Escape key to abort mux editing

• Start blindscanning the selected spectral peak by pressing the Blind button which tells neumoDVB that it should ask the drivers for a blindscan, i.e., it should take the tuning parameters as a starting point only and find the correct values itself. This should really be activated by default but it is not.

• Press 'Tune` to start the blindscan process.

If all goes fine, several pieces of information appear in the bottom part of the screen:

The following panels will show various information:

• At the bottom left, the Signal Panel shows SNR and signal levels. The different colours in the graphs have the following meaning:

  • the red part indicates values which are really too low for any reception;

  • the yellow region indicates levels that are poor, but should still allow viewing;

  • the green parts indicate signal levels well above what is needed, i.e., with a good rain fade margin.

  Note that RF level is usually not very important for good reception, but SNR is. There is also a bit error indicator, which shows the error rate before error correction. This is an indicator of signal quality. A non-zero value indicates poorer quality, but it does not necessarily mean that the DVB stream contains many errors.

  Below the signal level indicators, there are a number of indicator labels indicating the current lock status. Blue means that the result is good. Red means that the corresponding status is not yet OK. Once sync becomes blue, data is streaming properly from the drivers;

  The other info shown is:

  • LNB LOF offset shows the different between the current local oscillator frequency of the LNB and the correct value. LNBs with inaccurate local oscillators can result in frequency offsets as large as 2 Mhz, which makes it very difficult to tune to low symbol rate muxes. neumoDVB detects learns to compensate for this offset. So if you experience problems with low symbol rate muxes, just tune to many high symbol rate muxes in the same frequency band. Gradually the compensation will improve and neumoDVB will also start tuning to the low symbol rate muxes correctly.

  • MATYPE shows data about the current DVB-S2 modulation scheme.

  • PLS shows the Physical Layer Scrambling properties, "ROOT-1" in the example.

  • ISI shows the number of multi-streams on this mux between brackets, followed by the list of the stream_ids, or -1 in case the mux is not a multi-stream.

• The LNB and sat panel allows selecting another LNB, so that the next spectrum or blind scan can operate on another LNB without having to close the spectrum screen and return to the LNB screen. As the LNB can be on a rotor, it may also be necessary to select the desired satellite using the Sat combo-box. The Save button then saves some information for the LNB such as the default mux. The Reset LOF box can be used to reset the LOF offset estimate, which is gradually updated with each successful tune.

• The Service information panel shows information retrieved from the muxes SI tables, if any exist.

  • PAT, NIT, SDT turn black after having seen that type of SI data in the stream, without having necessarily processed all of it yet, i.e., service and mux scan is not necessarily finished when the indicators become black. It becomes blue when all of the table is processed. Some muxes do not transmit NIT or SDT.

  • "fin" indicates the overall status of SI scanning. It turns blue when scanning is done. This can take a while.

• The Constellation panel shows recent constellation samples. The example shows 8 clusters, so this is mux uses PSK-* modulation. The ``Update` toggle button enables or disables the constellation display.

• The Tune mux panel allows you to pick an already known (earlier scanned) mux from a list. This is very handy if your drivers do not support blind scan, because it will copy the proper tuning parameters, such as symbol rate, PLS codes and such. You can still use blind scan if you want.

  • At the very bottom, you can enter tuning parameters directly. This allows you to also tune frequencies not detected during spectrum scan. It is however very unlikely that such frequencies will tune. A more practical use case is when tuning to low symbol rate muxes. If blind scan fails, you may wish to retry with slightly different frequencies and symbol rates. Blind scan is supposed to correct frequency and symbol rate values itself, but the value you enter are used as startup hints.

    If blind scan is off, you need to check the tuning parameters carefully, because some may be at wrong values due to earlier editing. Wrong values for some parameters, such as stream_id or PLS code may even prevent "blind" tuning;

  • The reset button sets the tuning parameters to those found in the selected mux which appear below Tune mux;

  • The Tune button starts tuning;

  • The ABort button stops tuning;

  • The Pls Srch starts a search procedure to look for an unknown PLS code. This procedure is very time consuming: it can take up to an hour. It is also error prone and may not find the correct value. neumoDVB has a built-in list of known PLS-code, so on any muxes, the correct PLS codes will be found even without this feature. Also some cards, those based on m88rs6060, can discover PLS codes simply by tuning. neumoDVB automatically discovers the PLS data in this case.