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

[SteveBz]

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()

 

[SteveBz]

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):

[Victor Boesen]

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):

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!

[SteveBz]

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.

[SteveBz]

On 22/03/2022 at 10:57, SteveBz said:

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 March 27, 2022 by SteveBz

[SteveBz]

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

Edited March 27, 2022 by SteveBz

[Victor Boesen]

25 minutes ago, SteveBz said:

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 50 km/s

(Still) Looks great

Edited March 27, 2022 by Victor Boesen

[SteveBz]

4 minutes ago, Victor Boesen said:

Looks great

Sorry. I've just changed it 😅

[SteveBz]

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

But then occasionally, I get one of these:

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.

[SteveBz]

Here's a similar one, but this one is offset in the other direction.  Just look at the main features.

Edited April 3, 2022 by SteveBz

[Victor Boesen]

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.

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

Edited April 3, 2022 by Victor Boesen

[SteveBz]

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.

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.

[SteveBz]

Did you see this?

 mit_21cm_radio_telescope_JLExp_46.pdf

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

Kind regards

Steve.

[Victor Boesen]

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

[SteveBz]

Nice.  So look at this:
 

Versus this:

It looks left-to-right.

Steve.

[Victor Boesen]

10 minutes ago, SteveBz said:

Nice.  So look at this:
 

Versus this:

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

Victor

Edited April 3, 2022 by Victor Boesen

[SteveBz]

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

Victor

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

[Victor Boesen]

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

[SteveBz]

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.

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.

[Victor Boesen]

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

[SteveBz]

2 minutes ago, Victor Boesen said:

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

But is it the right way round?

[SteveBz]

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.

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.

[Victor Boesen]

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 

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

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

[SteveBz]

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.

[SteveBz]

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.