Jump to content

Banner.jpg.b6007b69ccdf5c69bf18273ddfe023df.jpg

21cm band. Refurbishing the dish with a new Cantenna.


Recommended Posts

Here's the code:

import os
import json
# Main method
# Generates and saves a GIF of 24H observations
def main():
    arr_txt = [x for x in os.listdir('Spectrums/clean') if x.endswith("json")]
    for fileName in arr_txt:
        path = f'Spectrums/clean/{fileName}'
        f = open(path)
        # Get RA
        sub1=fileName.find('ra=')+3
        sub2=fileName.find('dec=')-1
        ra=fileName[sub1:sub2]
        
        # Get DEC
        sub1=fileName.find('dec=')+4
        sub2=fileName.find(',.json')-5
        dec=fileName[sub1:sub2]
        # returns JSON object as
        # a dictionary
        record = json.load(f)
        data_dict=record['Data']
        freqs=data_dict['Freqs']
        values=data_dict['Data']
        maxValue=max(values)
        print(ra, dec, maxValue)

if __name__ == "__main__":
    main()

 

Link to comment
Share on other sites

Hi People,  I've created a matplotlib version with velocity as colour, but I'm not sure it works. Does this makes any sense? It's supposed to be blue is negative (ie coming towards us) red is positive (ie going away):

image.thumb.png.78660dc03a8da98f0555bddb39d7b888.png

  • Like 1
Link to comment
Share on other sites

4 minutes ago, SteveBz said:

Hi People,  I've created a matplotlib version with velocity as colour, but I'm not sure it works. Does this makes any sense? It's supposed to be blue is negative (ie coming towards us) red is positive (ie going away):

image.thumb.png.78660dc03a8da98f0555bddb39d7b888.png

Definitely makes sense! Good work;) I think, however, the red data-points are likely from noise as the signal gets weaker. Not much to do about it though!

  • Like 1
Link to comment
Share on other sites

12 minutes ago, Victor Boesen said:

I think, however, the red data-points are likely from noise as the signal gets weaker. Not much to do about it though!

I was just sitting here thinking that too.

Link to comment
Share on other sites

Posted (edited)
On 22/03/2022 at 10:57, SteveBz said:

1071839771_raadec51.1.gif.f5854e0accb21b6b6e8cd48201c20b60.gif

And here is 24 hour's worth.

 

Except if you look at this, the peak at 320 degrees should be a bit Blue and the peak at 75 should be a bit Red.  I think I need to check again.  The brown signal in the middle is definitely noise though.

Steve.

Edited by SteveBz
Link to comment
Share on other sites

Posted (edited)

I've just stretched the scale.  Is this the right way round, do you think?

I've put the colour scale between -50 and plus 30 km/s

image.png.dc95236fccdb583615dac09784e85736.png

Edited by SteveBz
  • Like 2
Link to comment
Share on other sites

25 minutes ago, SteveBz said:

I've just stretched the scale.  Is this the right way round, do you think?

image.png.8329989af8919b96879ec40e260c9162.png

I've put the colour scale between -50 and plus 50 km/s

(Still) Looks great:thumbright:

Edited by Victor Boesen
  • Like 1
Link to comment
Share on other sites

On 24/03/2022 at 09:10, SteveBz said:

But then occasionally, I get one of these:

414824358_ra313.2dec51.1.thumb.png.af53d11d27cbdc054b55a35e7c9993f0.png

And everything seems worthwhile 😀

Hi @Victor Boesen, I'm not sure that the image for the Milky Way is quite right.  Is it a little offset to the right?  My peak amplitude comes at about 10 degrees higher RA than indicated (ie 10 degrees leftward).  I first thought my rig was a bit out, but actually, now I'm not sure of the map.  Obviously my setup is rusty and shaky, but I think it's pointing more or less North.  Maybe it's a bit of both.  Could you check, do you think?

Kind regards,

Steve.

Link to comment
Share on other sites

43 minutes ago, SteveBz said:

Hi @Victor Boesen, I'm not sure that the image for the Milky Way is quite right.  Is it a little offset to the right?  My peak amplitude comes at about 10 degrees higher RA than indicated (ie 10 degrees leftward).  I first thought my rig was a bit out, but actually, now I'm not sure of the map.  Obviously my setup is rusty and shaky, but I think it's pointing more or less North.  Maybe it's a bit of both.  Could you check, do you think?

Kind regards,

Steve.

Hmmm I'm not sure anything is wrong with the map. It has matched up with my experience/observations and it's the exact same map that Pictor and Virgo uses. How are you measuring the RA position of your antenna? If you can, you could try to receive telemetry from Elektro L2 as a know location in the sky.

image.png.194215348a22d79b8e326cf50451d111.png

Its frequency is somewhere around 1690-1700MHz and it's a narrow pulsing signal.

Edited by Victor Boesen
  • Like 1
Link to comment
Share on other sites

1 hour ago, Victor Boesen said:

Hmmm I'm not sure anything is wrong with the map. It has matched up with my experience/observations and it's the exact same map that Pictor and Virgo uses. How are you measuring the RA position of your antenna? If you can, you could try to receive telemetry from Elektro L2 as a know location in the sky.

image.png.194215348a22d79b8e326cf50451d111.png

Its frequency is somewhere around 1690-1700MHz and it's a narrow pulsing signal.

I was using a compass, but as there is a lot of iron in it anyway, the compass may not be accurate 😅

Also, a little offset on the waveguide could throw the orientation.  I'll check against Polaris on the next clear night.  That's only 0.7 degrees out.

I've run 51 degrees N, and now I'm running 41. I hope to run 31, 21, 11 and 61 all this week and map them. We'll see how it goes.  I thought I'd try  for a flattened rotation curve!

Kind regards,

Steve.

Link to comment
Share on other sites

15 minutes ago, SteveBz said:

Did you see this?

  mit_21cm_radio_telescope_JLExp_46.pdf 253.13 kB · 0 downloads

Have you tied your own observations to the chart on page 7?

Kind regards

Steve.

No, I mostly used this simulator, which my observations matched quite well with.

https://www.astro.uni-bonn.de/hisurvey/euhou/LABprofile/index.php

Link to comment
Share on other sites

10 minutes ago, SteveBz said:

Nice.  So look at this:
 

raq309.thumb.PNG.001ee94f986b587cb5c2fa46084195a5.PNG

Versus this:

i_4635_41_-1_11.30_-400.00_400.00.png

It looks left-to-right.

Steve.

Yes! That bugged me too, until I discovered the plots SHOULD be mirrored. The simulated spectrum is showing the radial velocity whereas I'm showing the doppler. These essentially have opposite signs:

radial_vel = -doppler_vel

So you spectrum lines up very well with the simulated spectrum:thumbright:

Victor

Edited by Victor Boesen
  • Like 1
Link to comment
Share on other sites

11 minutes ago, Victor Boesen said:

Yes! That bugged me too, until I discovered the plots SHOULD be mirrored. The simulated spectrum is showing the radial velocity whereas I'm showing the doppler. These essentially have opposite signs:

radial_vel = -doppler_vel

So you spectrum lines up very well with the simulated spectrum:thumbright:

Victor

OK, so I totally misunderstood this.  Radial velocity is away from us and Doppler is towards us! Hmm. Perfect.  I understand now.

  • Like 1
Link to comment
Share on other sites

12 minutes ago, SteveBz said:

OK, so I totally misunderstood this.  Radial velocity is away from us and Doppler is towards us! Hmm. Perfect.  I understand now.

Correct! At least when the corresponding velocity is positive:thumbright:

  • Like 1
Link to comment
Share on other sites

Here's my sky-scan halfway through (3 days to go for the first pass - every 10 degrees from 10-60 inclusive) then maybe another five days to get it every 5 degrees 10-60.  But the key question is, have I got it the right way round.  Colour is velocity and length of vertical bar is intensity.  So it seems that Cygnus at around RA=300 (and presumably therefore the Cygnus arm) is rotating away from us, and that the other arm (is it Perseus?) is rotating towards us.  I'll update it in a few days when I get the other scans.

Figure_1.thumb.png.99ab59f03930d9807065de4e95611aa7.png

Is this representation working for you?  Do you think It's intuitive?

I've also applied a little noise damping by averaging out the signal between RA=150 and RA=225, and DEC = 0-90 and subtracting it from everything.

Anyhow, please let me know what you think.

Kind regards,

Steve.

  • Like 1
Link to comment
Share on other sites

14 minutes ago, SteveBz said:

Is this representation working for you?  Do you think It's intuitive?

Definitely intuitive to understand. Look forward to see some rows being added to it:thumbright:

  • Like 1
Link to comment
Share on other sites

2 minutes ago, Victor Boesen said:

Definitely intuitive to understand. Look forward to see some rows being added to it:thumbright:

But is it the right way round?

Link to comment
Share on other sites

So here is the final image.  About a week of scans.  The top row and the bottom row seem to have a bit of a weaker signal.  I think because of the roof at one side and the tree-line on the other.  Also a few samples missing from the dec=61 degrees line.

image.thumb.png.43deed66a96e2d158527620e9a3ed641.png

It would really benefit from running for another week in the middle of the garden, but I'm not sure I have the patience.

What should I do next, do you think?  I guess either try to plot the arms of the Milky Way or see if I can get a rotation curve.  Not sure I have enough samples for either of these. I can probably only get about ten to 15 points where the signal intersects the plane of the Galaxy. 

Kind regards,

Steve.

  • Like 1
Link to comment
Share on other sites

Sorry, been a bit busy last couple of days! The plot looks great (and correct!), but I do think it would help with a couple more scans as you say :thumbright:

I will give you a little spoiler as for what I've been messing around with lately:grin:

image.png.a64dccce5e5446010f9214ed71b4785f.png

Doing this as a part of my long awaited rewrite, which I'm currently working on. I have decided to ditch the command line options simply because there were so many, that they were cumbersome to work with. Instead, all settings will be available through the config.json or by using the UI. This way one does not depend on the UI when using the software, which is and has always been an important part for me to maintain, as many people are likely using it headless on a Raspberry pi!

Victor

  • Like 1
Link to comment
Share on other sites

12 hours ago, Victor Boesen said:

Doing this as a part of my long awaited rewrite, which I'm currently working on. I have decided to ditch the command line options simply because there were so many, that they were cumbersome to work with. Instead, all settings will be available through the config.json or by using the UI. This way one does not depend on the UI when using the software, which is and has always been an important part for me to maintain, as many people are likely using it headless on a Raspberry pi!

Very nice, I totally agree.  Can I make 2 observations:?

1) the gif-maker never works until I run Mogrify on it and reduce the size of the .png files, so obviously the automatic gif at the end of 24 hours also always fails.  On my copy I've stripped that out and then I

mogrify -resize 2000x585 *.png

Before run my stripped-out vesion of 'gif'

2) Secondly, I love the debug data-dump, so I always save it in the 24 hr scan, then I have a second python program to extract the data and map it (as you saw).  I also save many more parameters in the .json file than you do, eg datetime, l & b coords and some other stuff.

  • Thanks 1
Link to comment
Share on other sites

My last question is this.  What about planetary movement?  The velocities I measure are about +20 km/s -> -60 km/s.

Planetary rotation is about .5 km/s, so doesn't really matter, but revolution around the sun is a bigger deal:

speed = 150e6*2pi/(365*24*3600) km/s
speed = 30 km/s

So really the velocities should be adjusted by the position of the Earth in respect to the Sun and I'm not sure how to do this. 

What do you think?

Kind regards

Steve.

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.