Hydrogen line help

[Lucas Barclay]

Good evening all,

I am currently tearing my hair out at why I keep seeing these peaks along the hydrogen line and I so far have had no success in observing the actual hydrogen line peak.. I was wondering if someone had an answer to the issue at hand here.. Is this normal to see or is there something completely wrong? Any help is greatly appreciated!

[Ed astro]

Hi Lucas,

the narrow spikes are all RFI, although I can not tell you where it comes from (maybe a switching power supply or a computer near the antenna?) 

the hydrogen line signal is quite weak- usually no more than 0.5 to 2 dB above the noise floor. You can change the vertical scale in the IF average plot with the “gain” and “level” sliders to make the weak signals more easily visible, or you can export the spectrum as a .txt file and plot it in excel. 

If you already tried that and still see nothing then there is probably some technical issue…

By the way, could you give us a short description of the setup you are using?

Best regards,

Eduard

Edited February 11, 2022 by Ed astro

[Lucas Barclay]

1 hour ago, Ed astro said:

Hi Lucas,

the narrow spikes are all RFI, although I can not tell you where it comes from (maybe a switching power supply or a computer near the antenna?) 

the hydrogen line signal is quite weak- usually no more than 0.5 to 2 dB above the noise floor. You can change the vertical scale in the IF average plot with the “gain” and “level” sliders to make the weak signals more easily visible, or you can export the spectrum as a .txt file and plot it in excel. 

If you already tried that and still see nothing then there is probably some technical issue…

By the way, could you give us a short description of the setup you are using?

Best regards,

Eduard

Ahh interference could be it since I have only been testing my setup in my room nearby to my computer and other devices.. Is there a specific frequency for the hydrogen line to focus on by any chance? My setup definitely isn't the best as I've tried to work with cardboard and tin foil. I made a horn antenna as seen below, it definitely isn't the best construction but I thought I may be able to see some results from it. The waveguide is 15cm by 15cm and the copper core is roughly 5cm in length. I think I have a complete circuit by keeping the outer copper mesh in contact with the foil lined on the inside but I may be wrong.. I use a generic nooelec rtl-sdr and I also use the sawbird hydrogen line filter to try and increase my chances of receiving a signal. 

 

Thank you for the response!

[Ed astro]

I am not sure whether the dimensions of the waveguide are right but even though the antenna may not be ideal it is still definitely worth trying to detect the hydrogen line! See for example this project where HI was detected with an antenna made from a paint can: http://parac.eu/projectmk9.htm

The probe length of 5 cm should be OK, maybe it is a few mm too long (in my can feed it is 4.6 cm) but the few mm difference probably does not degrade the performance too much. Probe placement with respect to the back of the waveguide is quite critical but should be about 8 cm. Another thing that can really help is mounting the LNA as close as possible to the probe in order to minimize cable losses. 

Have you already tried to observe outside with the Milky Way overhead? Inside you will probably only receive the thermal emission of the ceiling… 

The frequency of HI is 1420.405752 MHz plus or minus about 1 MHz due to Doppler shift, but usually the strongest peak is close to the rest frequency.

Best regards,
Eduard

 

[SteveBz]

On 11/02/2022 at 17:15, Lucas Barclay said:

Good evening all,

I am currently tearing my hair out at why I keep seeing these peaks along the hydrogen line and I so far have had no success in observing the actual hydrogen line peak.. I was wondering if someone had an answer to the issue at hand here.. Is this normal to see or is there something completely wrong? Any help is greatly appreciated!

Hi Lucas,

How did you set up the radio? I'm just waiting for parts at the moment and I'd love to see how other people are doing it.

Steve.

[Lucas Barclay]

2 hours ago, SteveBz said:

Hi Lucas,

How did you set up the radio? I'm just waiting for parts at the moment and I'd love to see how other people are doing it.

Steve.

Oh! Well this is actually the second time I've tried making a cone antenna and this is the largest I've made so far.. I mostly used a bunch of amazon boxes to construct it and after realizing I didn't have much, I decided to create a mesh instead for the foil to wrap around. Of course this sacrifices durability and structure but hopefully it should still work! With the probe I didn't have a special adapter so I have made sure to keep the outer mesh in contact with the foil on the inside and the copper core probe separate. At the moment I am trying to get it to work on my windows computer but once I see a sign of the hydrogen line I'm planning to try and automate it on the raspberry pi and build a map of the milky way (I may also turn it into a community project on my website if possible). I haven't attempted putting it outside yet but I'm planning to tomorrow hoping that it doesn't decide to rain (or rip apart my antenna..). I will give an update once I attempt this!

[Lucas Barclay]

On 11/02/2022 at 22:10, Ed astro said:

I am not sure whether the dimensions of the waveguide are right but even though the antenna may not be ideal it is still definitely worth trying to detect the hydrogen line! See for example this project where HI was detected with an antenna made from a paint can: http://parac.eu/projectmk9.htm

The probe length of 5 cm should be OK, maybe it is a few mm too long (in my can feed it is 4.6 cm) but the few mm difference probably does not degrade the performance too much. Probe placement with respect to the back of the waveguide is quite critical but should be about 8 cm. Another thing that can really help is mounting the LNA as close as possible to the probe in order to minimize cable losses. 

Have you already tried to observe outside with the Milky Way overhead? Inside you will probably only receive the thermal emission of the ceiling… 

The frequency of HI is 1420.405752 MHz plus or minus about 1 MHz due to Doppler shift, but usually the strongest peak is close to the rest frequency.

Best regards,
Eduard

 

By the looks of things I'm still not receiving anything on the hydrogen line.. Is there a possible rig you would recommend for doing radio astronomy? I can't seem to find any antenna or satellite dishes that are suited for the hydrogen line.. Could I have done something wrong with the wiring too?

[Ed astro]

The wiring should be relatively straightforward; I assume you have a coax cable between your amplifier and your SDR and probably a short bit of coax between the amplifier and your antenna. It could of course be the case that one of the connectors is bad, or that the bit of cable or the connector between the amplifier and the antenna is too lossy.

You could also check whether the amplifier is working: when you power it up you should see your spectrum jump up. 

If it all does not work with your current antenna you could try to make a simple "coffee can" feed; these are fairly simple to make from a paint can or a piece of stove pipe with the right dimensions and work really well as a minimal setup for detecting HI (see for example the link in my previous post). Once you have made a working setup with this you can scale up by using the antenna as a feed for a satellite dish or use it as the basis for a conical horn antenna.

[Carl Reade]

Hi you will also need to know where and when the Milky way will pass through the horn. Stellarium  software etc.

Carl