Blind Scan in DVB Dream
DVB Dream™ ver.3.0 introduced a new feature, BlindScan.
Corresponding additional functions are exposed in the new DVB Dream API. This allows DVB card manufacturers and 3rd party programmers to fully utilize BlindScan interface of DVB Dream.
DVB Dream SkyWalker-3 interface (gp_sw3.dev, starting from ver.1.0.4) now supports BlindScan as well. SkyWalker-3 firmware has to be upgraded to a new version (2.05.7) to support BlindScan.
DVB Dream BlindScan interface is accessible through Main Menu -> Tools -> Blind Scanner (the following screenshots were made with a private development version of DVB Dream, final public version can have slight modifications in the interface/format/color palette):
In the top line of Blind Scan interface, you can adjust Start/Stop frequencies and the frequency Step size for Spectrum Acquisition. You can adjust additional parameters for Blind Scan and Spectrum Acquisition in the Options tab (click on the image to open it at a higher resolution in a new window).
Parameters affecting the Spectrum Acquisition speed and spectrum quality:
Wait time: it's a time delay in milliseconds between commands SetTunerFrequency() and GetSignalStrengh() sent to the tuner (for each point of the Spectrum). The shorter the wait time the faster Spectrum Acquisition will be (though accuracy will be diminished, and some artifacts can appear). 1-25ms range is a typical adjustment range for SkyWalker-3 (shorter delays for slow PC, longer delays for faster PC).
If you set 0 ms, SkyWalker-3 driver will use 20 ms instead (default value).
BW / Symbol Rate: sets the bandwidth of RF tuner during Spectrum Acquisition, indirectly set by setting Symbol Rate for the digital tuner (this is for Spectrum Acquisition only, it does not affect Blind Scan capability to find proper Symbol Rate). Lower BW value can improve the resolution of the Spectrum (though, longer wait time will be required for each spectrum point). 4000 Ksps is a good starting point for BW value for SkyWalker-3, even if your frequency step size is just 1MHz. I rarely use any other values.
All other parameters are not used during Spectrum Acquisition.
Parameters affecting the Blind Scan speed and quality:
Please leave values for wait time and BW the same as during Spectrum Acquisition (Blind Scan algorithm is using them for rough spectrum acquisition, graph is not displayed, it is used for internal calculations only).
Symbol Rate range: Blind Scan algorithm evaluates every point of the spectrum and when it finds the potential transponder it starts Blind Tuning process. Obviously, the wider the allowed Symbol Range the longer the Blind Tuning process (more iterations are required). It is Minimal Symbol Rate which affects the duration of the Blind Tuning process (the Maximum Symbol Rate hardly affects the speed and can be always set to 45 Msps). If you don't expect to find narrow bandwidth transponders, set the Min Symbol Rate appropriately (set 4500 if all expected transponders have symbol rate 4600 Ksps or higher). This well reduce the Blind Tuning process noticeably.
Step KHz: "micro-step" size. It is used during evaluation of the RF signal during blind micro-stepping. If two adjacent points give identical evaluation score, there is a big chance that potential transponder is detected. Thus, smaller micro-step values (approximately 250 KHz) are advised to detect narrow bandwidth transponders (3-5 Msps). Obviously, smaller micro-step prolong the blind scan process. To speed up the process (especially if you don't expect narrow bandwidth transponders on that satellite) you can set larger micro-steps (1000 KHz works just fine for transponders with symbol rate 15 Msps and higher).
Auto tune range KHz: this parameter tells the tuner how far from the requested frequency it can auto-adjust the actual frequency when tuning to transponder. If set high, tuner will eventually "snap" to transponder peak frequency if this peak is within the desired range of requested frequency. This will help to find a transponder faster during blind scan. At the same time, this high value can prevent the scan algorithm to detect relatively weak transponders situated next to the strong transponders (especially, if they have the same symbol rate). This is because frequency auto-adjust process will simply snap to the stronger transponder if it is within the same frequency range from requested frequency. Usually, I use 2000-5000 KHz values (lower values if I expect narrow bandwidth transponders sitting next to each other, and higher values otherwise).
Power Threshold: Blind Scan algorithm will skip all Spectrum sections from analysis if they are below the threshold. Often, if the signal is below -62dBm, SkyWalker-3 can not lock that transponder properly. Thus I often set threshold to -62 dBm. Your threshold can be different (it depends on the size of the dish, LNB quality and signal loss in the coax cables and switches).
Blind Scan tab of this interface contains Start/Stop buttons for blind scan, alone with the window to report detected transponders. Scroll bar at the top of the Blind Scan interface indicates approximate progress of the Blind Scan process, you can interrupt it any time with a Stop button.
After the Blind Scan is finished (or interrupted), you can double-click on one of the detected transponders in the list. This will open Manual Scan dialogue (pre-filled with the parameters of that transponder), where you can scan for the channels and either save or discard them.
Or you can use Save Menu button to add parameters of newly found transponders to existing INI file (and scan them later).