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Updated Capture (markdown)

Brumi-2021 2023-08-15 10:10:11 +02:00
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Capture.md

@ -11,7 +11,7 @@ The Key Items on the App that can be selected with the cursor and changed with t
* **Rate:** The sample rate, which by its nature set the set bandwidth of capture. This is shown in the markers around the centre line of the waterfall display. The sample rate is variable from 12k5 to 2750K (*) in many steps. You need to ensure that the sample rate is more than twice the bandwidth of the signal you want to capture see [(Nyquist Principle / also called Shannon’s Law) ](https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem)
* **Format:** The user can select two file formats, of the recorded IQ data 16 / 8 bits : C16 (complex 16) or C8 (complex 8), and its related file extension ".C16" or "C8". (By default we are preselecting C16).
Note (*) : Currently , **for correct Replay application ,you should ONLY use Capture App selecting any Bandwith capture <= 1Mhz (but 500Khz is the recommended for majority micro SD cards compatibility because it requieres a quite common average write speed in our system >2MB/sec,C16)**. From 600khz till 1Mhz , you will need more fast and good quality micro sd card (with min average write speed >3MB/sec (for BW=750khz,C16) , and >4MB/sec (for BW=1Mhz ,C16), and with as small as possible write random latency. (In the GUI , those correct bandwidth capture options appear with the Normal usual "REC" icon Background colour, as user recomended BW capture options). If you face too much % dropped samples when recording , you can retry it reducing C16 to C8 , that also reduces the needed average write speed :2 (example 1Mhz rec will need average sd interface speed of 4MB/sec in C16 or 2MB/sec in C8).
Note (*) : Currently , **for correct Replay application ,you should ONLY use Capture App selecting any Bandwith capture <= 1Mhz (but 500Khz is the recommended for majority micro SD cards compatibility because it requieres a quite common average write speed in our system >2MB/sec,C16)**. From 600khz till 1Mhz , you will need more fast and good quality micro sd card (with min average write speed in our system >3MB/sec (for BW=750khz,C16) , and >4MB/sec (for BW=1Mhz ,C16), and with as small as possible write random latency. (In the GUI , those correct bandwidth capture options appear with the Normal usual "REC" icon Background colour, as user recomended BW capture options). If you face too much % dropped samples when recording , you can retry it reducing C16 to C8 , that also reduces the needed average write speed :2 (example 1Mhz rec will need average sd interface speed of 4MB/sec in C16 or 2MB/sec in C8).
Above 1Mhz bandwith options (with YELLOW REC button background Icon), in current fw version , the recorded files have periodical sample drops , and therefore it has not recorded all full original samples content and therefore it is NOT useful for the Replay App , just useful to check the spectrum image, example using the linux tool "inspectrum" or "Audacity") . Anyway when replaying those captured files , the replay time will be shorter than real . but normally you should still get a correct modulation, but in case of voice contents, it would sound , unnatural , "like with accelerated playing speed" , because in fact,due to Hackrf One System (HW+SW) limitations, those recorded files (under those high speed BW with YELLOW icon) have decimated its content - when recorded there were skipped some real time samples.
In future versions, it is pending to investigate and try to apply a correct .C16 recording files (without any samples drop) till a capture of 2Mhz. (We will keep updated that manual , when we achieve it)