Re: Looking for a way to plot V_LSR vs intensity in GNU Radio

[Paul Boven]

Hi Ellie,

On 7/24/20 5:09 PM, Ellie White wrote:
My question is this: do any of you know of a method -- or a GNU Radio 
module -- compatible with GR version 3.8 that allows you to plot raw 
data from a USRP and get a plot of intensity versus velocity with 
respect to the local standard of rest (V_LSR) -- instead of intensity 
versus frequency, as given by the time sink block?


We solved this somewhat differently: I wrote some Python code that, 
given Ra/Dec (which we can get from the telescope) and 
date/time/position, calculates the V_LSR for that viewing direction. The 
calculation itself is done in Astropy, hence the need for Python3, and 
the reason we upgraded to GR 3.8 as soon as we could. One of our other 
volunteers wrote a Telescope class that can be queried for pointing 
direction and the like.


The frequency offset is calculated every second, and sent back into the 
flowchart using ZMQ. The ZMQ sink sends the tuning commands to a 
frequency-translating-fir block to shift the received frequency 
automatically. The advantage of using this method is that the frequency 
bins for the FFT integration stay at the same V_LSR during long 
observations, or observations carried out at another date/time, so you 
don't need to resample/interpolate to compare.


As we show the integrated spectrum using the Vector Sink anyway, it's 
very easy to have it calculate the x-axis labels in terms of doppler 
velocity, instead of frequency.


We took some extra effort that the doppler shift calculation can simply 
be included in the flowchart, and starts/stops with the flowchart.


Happy to send you some code, although some of it is specific to the 
Dwingeloo telescope.


Regards, Paul Boven.

Re: Looking for a way to plot V_LSR vs intensity in GNU Radio

[Marcus D. Leech]

On 07/24/2020 12:17 PM, Marcus Müller wrote:

Hi Ellie,

being not versed in radioastronomy, I need to guess a bit here, but:
Is what you want essentially "how much power is there for any Doppler 
shift"?


If that's the case, and you're observing some known-frequency emission 
(say, a Hydrogen line) would that basically amount to:


1. Frequency-Shifting so that the zero-doppler frequency ends up at 0 Hz
2. transforming your time domain observation to frequency domain
3. labeling the frequency axis so that it tells velocity?

In that case, the Qt GUI frequency case would be a way to go. You can 
set the center frequency to do 1., it inherently does 2. and 3. can be 
achieved (ignoring wrong physical unit labels) by adjusting the 
bandwidth parameter.


Cheers,
Marcus

In spectro_radiometer, I use the Qt Vector plotter, and use some math to 
display km/sec on what would normally be the frequency axis.  This

  calculation doesn't account for the VLSR, but it certainly could.

Re: Looking for a way to plot V_LSR vs intensity in GNU Radio

[Marcus Müller]

Hi Ellie,

being not versed in radioastronomy, I need to guess a bit here, but:
Is what you want essentially "how much power is there for any Doppler 
shift"?


If that's the case, and you're observing some known-frequency emission 
(say, a Hydrogen line) would that basically amount to:


1. Frequency-Shifting so that the zero-doppler frequency ends up at 0 Hz
2. transforming your time domain observation to frequency domain
3. labeling the frequency axis so that it tells velocity?

In that case, the Qt GUI frequency case would be a way to go. You can 
set the center frequency to do 1., it inherently does 2. and 3. can be 
achieved (ignoring wrong physical unit labels) by adjusting the 
bandwidth parameter.


Cheers,
Marcus

On 24/07/2020 17.09, Ellie White wrote:

Hey all!

Hope you're doing well and having a good summer. I apologize for 
cross-posting here, but I wanted to pass this question by members of 
both the SARA and GNU Radio communities to see what resources are out 
there. This summer I'm working as an intern for Berkeley SETI Research 
Center and I'm helping integrate the Allen Array with GNU Radio. I've 
been collecting data with a USRP on site and I'm now attempting to plot it.


My question is this: do any of you know of a method -- or a GNU Radio 
module -- compatible with GR version 3.8 that allows you to plot raw 
data from a USRP and get a plot of intensity versus velocity with 
respect to the local standard of rest (V_LSR) -- instead of intensity 
versus frequency, as given by the time sink block?


Thanks so much for considering this, and for any ideas you have to 
share! Have a nice day and take care.


Cheers,
Ellie

--
Ellie White
Co-Director, Open Source Radio Telescopes
Student at Marshall University
304-654-9381
www.catseyeenterprises.net 

Looking for a way to plot V_LSR vs intensity in GNU Radio

[Ellie White]

Hey all!

Hope you're doing well and having a good summer. I apologize for
cross-posting here, but I wanted to pass this question by members of both
the SARA and GNU Radio communities to see what resources are out there.
This summer I'm working as an intern for Berkeley SETI Research Center and
I'm helping integrate the Allen Array with GNU Radio. I've been collecting
data with a USRP on site and I'm now attempting to plot it.

My question is this: do any of you know of a method -- or a GNU Radio
module -- compatible with GR version 3.8 that allows you to plot raw data
from a USRP and get a plot of intensity versus velocity with respect to the
local standard of rest (V_LSR) -- instead of intensity versus frequency, as
given by the time sink block?

Thanks so much for considering this, and for any ideas you have to share!
Have a nice day and take care.

Cheers,
Ellie

-- 
Ellie White
Co-Director, Open Source Radio Telescopes
Student at Marshall University
304-654-9381
www.catseyeenterprises.net