Re: [Discuss-gnuradio] Units of data saved by filesink

On 07/25/2019 01:24 PM, Ellie White wrote:

Hi Marcus,

Good to know. So how would you recommend I should convert these values to, say, watts? (I guess perhaps it would be watts squared due to the mag to mag squared block). I assume I would first have to determine what the SDR considers full scale -- do you have any suggestions on how to do that? 

Thank you so much for your time and input on this, I really appreciate it! 

Take care,

Ellie

Ellie:

For microwave radio astronomy, placing a carbon-foam RF absorber sheet over the feed aperture (if that's possible here) gives you a known
  blackbody temperature source at <whatever the ambient physical temperature is in Kelvins>.   Once you know that, then you know that the
  output of your SDR processing chain is proportional to:

Tabsorber + Tsys

Pointing your feed horn (again, I'm assuming something microwavey here, like 21cm) at the North Celestial Pole at night will give you a good
  approximation to roughly 10K sky temperature (maybe a little more or less).  THAT reading will be proportional to:

Tsky + Tsplillover + Tsys

With a pyramidal horn antenna (which is what I think you've been working with), Tspill should be very small, perhaps 1 or 2K.  For a dish
  antenna, it's usually a bit more (perhaps 10K).


Assuming Tsys doesn't change much between those two readings, you now have a couple of calibration points that you can use to determine
  power readings as seen at the front of your RF chain.

On Thu, Jul 25, 2019 at 1:11 PM Müller, Marcus (CEL) <mueller@kit.edu> wrote:

Arbitrary counts, relative to what your Device and the attached DSP you
or the device are doing considers full scale.

Best regards,
Marcus

On Thu, 2019-07-25 at 13:09 -0400, Ellie White wrote:
> Hi all,
>
> Hope you are doing well! I have been working on a flowgraph (attached) that will allow me to process and save data samples from an Ettus SDR (which is plugged in to a different computer -- the data is streamed over via a TCP socket). I am using a metadata filesink for this, and am curious to know, what are the units in which the data is saved? I.e., when I open the binary data file using a separate python program (such as the one attached), and plot the data as an averaged spectrum, what will the units on the y-axis be -- some actual physical unit, or an arbitrary counts unit?
>
> Any info that you can provide on this would be much appreciated -- have a great afternoon!
>
> Best,
> Ellie
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