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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) < address@hidden>
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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