[hpsdr] OpenPowerSDR RX recording question

[John Laur]

John,

For IQ recording you want to make sure the bandwidth of the receiver
(Setup->Audio->Primary->Sample Rate) is the same as the samplerate of the
recording (Wave->Options->Sample Rate) And I suggest recording as 32bit
float since that matches the internal representation of values. I think if
they are different then a resampler is employed, but it would be best to
simply have them the same.

The recording will therefore capture the entire bandwidth of the receiver
before the DSP. Note that if you are using stiched receivers it only
captures the first receiver (the one in the center)

So, yes, if you wanted to capture the entirety of field day CW on 20m you
could in theory do so using a 192khz samplerate, tuning to 14.075 then
recording. This would capture 13.979MHz to 14.171MHz. You could later
enable wav playback and tune around in this passband (using CTUN)

In practice, there are a couple of gotchas with WAV files that you may hit
with long recordings. The header format for standard wav only allows a 32
bit length, so PowerSDR may not properly create files > 4GB. There is a
standard called "Broadcast WAV" which extends this, but I do not know if
PowerSDR supports it and I would bet not. Finally, some applications will
poop on WAV > 2GB no matter what, so you might want to experiment with this
prior to attempting to create one monolithic recording.

To keep your IQ wav <2GB use the following maximum recording times (for
32bit float):

48KHz: 80min
96KHz: 40min
192KHz: 20min
384KHz: 10min

If you find that support for larger files works as you expect, this will
give you a pretty good idea of the space requirements. In your example,
capturing all of field day 20m CW/digital would consume 27 hrs * 6GB/hr
(@192KHz) = 162GB. According to some tests
http://rtl-sdr.better-than.tv/?page_id=233 FLAC compression might give you
a 20-40% reduction in final size if you postprocessed the wavs. I think
PowerSDR may not support FLAC compressed WAV though...

73, John K5IT

On Sun, Jul 5, 2015 at 2:52 PM, John <radio at mediacombb.net> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
>
>
>
> When record I & Q is selected in the Record Wave menu of OpenPowerSDR,
> what is the bandwidth recorded?
>
> Stated another way:  If I set to Receive at 14.048 CW, is the width of the
> recording  98 KHz?
> Is it the width of the spectrum display?  Or the RX bandwidth?
>
> What I'm getting at is, if I had enough hard drive space, could I record
> the whole CW band on 20 meters during Field Day and then later tune around
> the recording with OpenPowerHPSDR and listen to it just as if it were
> "live"?
>
> John,  WoGN
>
>
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