21 cm Hydrogen Line

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Michael Caba

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Mar 14, 2025, 3:04:16 PM3/14/25
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Hi friends.

I am scanning the 21 cm line with a Scope in the Box antenna. I can pick up the Hydrogen Line just fine.  But I also at times get dips in the reading such as shown in the attached image.  What do the dips represent?

The antenna was pointed at RA/DEC at a dip is 15h 25m 45sec  / 440  21'  35" at the time of the dip. 

Any info is appreciated. 

Thank you.

Mike Caba


HL Dip_1636.jpeg

Alex P

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Mar 14, 2025, 4:00:55 PM3/14/25
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How are you performing the IF_ave Background Correction ?

Use either a 50 ohm load (best) , or just open / not attached to the antenna ..

Alex


b alex pettit jr

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Mar 14, 2025, 4:04:04 PM3/14/25
to 'Alex P' via Society of Amateur Radio Astronomers
On Friday, March 14, 2025 at 04:01:01 PM EDT, 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:


How are you performing the IF_ave Background Correction ?

Use either a 50 ohm load (best) , or just open  LNA =  not attached to the antenna ..

Alex



Michael Caba

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Mar 14, 2025, 4:14:13 PM3/14/25
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Thanks Alex.

Is the 50 Ohm terminator  at the attached link a good bet?  


Thank you.

Mike

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Michael Caba

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Mar 14, 2025, 4:14:22 PM3/14/25
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Thanks Alex.

Is the 50 Ohm terminator  at the attached link a good bet?  


Thank you.

Mike

b alex pettit jr

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Mar 14, 2025, 5:09:42 PM3/14/25
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YES : I have those myself ..

Not sure how you acquired the correction for the data you posted, but it Contained some H1 info ..
and as the sky drifted by, you found an area of the sky with Less than the cal ..  
OR, the Dopplerfreq shifted .. either way the results are the same.



andrew....@googlemail.com

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Mar 14, 2025, 6:22:20 PM3/14/25
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I’m going to be really interested to find out what other people think this is, too! Don’t get it myself

Andy


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image001.jpg

Marcus D. Leech

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Mar 14, 2025, 6:24:58 PM3/14/25
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On 14/03/2025 18:22, andrew.thornett via Society of Amateur Radio Astronomers wrote:

I’m going to be really interested to find out what other people think this is, too! Don’t get it myself

Andy

It means that at the time that you took baseline data, there was some small amount of H1 being detected, and that got
  subtracted, leading to a "dip" shaped like the hydrogen emission that is in the baseline data.


Dr. Rich Russel

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Mar 14, 2025, 6:37:56 PM3/14/25
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What about a H1 absorption region?

Rich

Stephen Arbogast

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Mar 14, 2025, 6:51:13 PM3/14/25
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Ain't Physics, Electrical Engineering, Software fun?

Stephen Arbogast

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Mar 14, 2025, 6:54:38 PM3/14/25
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Watched all of the  Western Conference talks today..  wonderful!   .....a lot to think about.

Andrew Thornett

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Mar 14, 2025, 7:35:51 PM3/14/25
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Ahhh!.....but in my H-line talk, I didn't talk about a dip in the middle of the trace, because I haven't seen that before....so when we find out, I will be adding another slide to the talk for the future!

From: 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Friday, March 14, 2025 10:54:38 PM

To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] 21 cm Hydrogen Line
 

Stephen Arbogast

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Mar 14, 2025, 7:53:27 PM3/14/25
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I am  new at this...  I am  learning  and  experimenting. Even  with   many years in  EE, Physics and  Software there is  much to learn.  Currently  I am working  with Hl-3d  software  from Alex  Pettit.    I am learning  how to post process the  raw  data that I have collected. SARA  has  been very  helpful.... Thank you.

Andrew Thornett

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Mar 14, 2025, 8:10:30 PM3/14/25
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Good luck! I have just set up a H-line group for the British Astronomical Association. 
All SARA members are welcome to join this H-line group. It is aimed at beginners.
Several other SARA members are joining it - would you be interested?
If so let me know and I will send you link for 1st meeting.

Andy
From: 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Friday, March 14, 2025 11:53:27 PM

Bruce Rout

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Mar 14, 2025, 8:21:54 PM3/14/25
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Closest thing is a quasar SDSS J152556.92+442158.4 at 15h25m56.972m +44 21 58.2 which has a Z of 5.047783. Done know if that is any help at all.


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Stephen Arbogast

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Mar 14, 2025, 8:22:12 PM3/14/25
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Yes,  I  am  interested...   Thank you.

Michael Caba

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Mar 14, 2025, 8:25:54 PM3/14/25
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Ok. I bought the 50 ohm terminator and will try it when it arrives next week. Then I will post the results. I too think it is in the background recording. 

Mike



b alex pettit jr

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Mar 14, 2025, 8:32:34 PM3/14/25
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On Friday, March 14, 2025 at 08:25:56 PM EDT, Michael Caba <michae...@gmail.com> wrote:


Ok. I bought the 50 ohm terminator and will try it when it arrives next week. Then I will post the results. I too think it is in the background recording. 

Mike


YES, as stated in one of the early posts ,
 it is just that the background cal contained H1 signals.. 
and the decrease of that creating a 'below cold sky'  level  dip

Using a resistor for cal will provide a flat background ..

Alex


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