Anyone doing hydrogen line observing?

[Kaffeedor]

On 16/01/2020 at 01:01, Carl Reade said:

It will work fine. I think what UR is saying is the plate on the feed is a reflector which it is but not the main reflector.

Copper will need sprayed with a coating to protect it from the weather. Keep us updated on the build.👍

So now, two months later, I still haven't made first light. Software (I use Cotos VIRGO) is ready, feed is beside LNA done and I think I have a place to put it now.

My problem now is, I think I have destroyed my LNA... 

Does anyone here know a good and cheap(<30€) LNA that I has a USB plug onboard!! and doesn't need to be soldered anywhere? 

Thank you all,

Fedor

[Carl Reade]

On 17/03/2020 at 17:25, Kaffeedor said:

So now, two months later, I still haven't made first light. Software (I use Cotos VIRGO) is ready, feed is beside LNA done and I think I have a place to put it now.

My problem now is, I think I have destroyed my LNA... 

Does anyone here know a good and cheap(<30€) LNA that I has a USB plug onboard!! and doesn't need to be soldered anywhere? 

Thank you all,

Fedor

Hi there are quite a few options on eBay at that price. Wideband LNAs with a bias tee circuit or screw terminals for power. Why do you think yo destroyed your current one?

 Carl

[Kaffeedor]

15 hours ago, Carl Reade said:

Hi there are quite a few options on eBay at that price. Wideband LNAs with a bias tee circuit or screw terminals for power. Why do you think yo destroyed your current one?

 Carl

Hello,

I now ordered the (more expensive than eBay ones), 'Nooelec SAWbird+ H1 Barebones', as it has a Micro USB port as power connection. Should arrive on Monday

I wanted to resolder the '+' connection on the old one but then the 'Plate' were the connection was on the LNA got of and now there is no connection between '+' and anything other in the LNA. Also one of SMA connections is tilted slightly

Unrelated:

How young is the youngest person you know of who build a Radio Telescope?

Do you know good books/magazine related to Radio Astronomy? 

Fedor

Edited March 19, 2020 by Kaffeedor

[Carl Reade]

Hi not sure who the youngest would be. Not too many magazines on the subject it's a small sport. SARA group is very good to join.

This site has been invaluable for me the CFRAD software works great. Have a read at the projects section particularly 3 and 9 to see what is achievable with the basics.

http://parac.eu/

[gabrielxp46]

What materials do I need to build a radio telescope for hydrogen line? What program do I use to obtain and analyze the data?

[gabrielxp46]

What materials do I need to build a radio telescope for hydrogen line? What program do I use to obtain and analyze the data?

[gabrielxp46]

What materials do I need to build a radio telescope for hydrogen line? What program do I use to obtain and analyze the data?

[Carl Reade]

9 hours ago, gabrielxp46 said:

What materials do I need to build a radio telescope for hydrogen line? What program do I use to obtain and analyze the data?

Hi if you have a read through the thread most of what you are asking is in there.

[gabrielxp46]

What is the minimum distance between the PC and the antenna so that there is no interference between the equipment?

[Carl Reade]

10 hours ago, gabrielxp46 said:

What is the minimum distance between the PC and the antenna so that there is no interference between the equipment?

Hi probably around a minimum of 5 meters of distance from radio gear to PC. It would also be beneficial to have the receiver in a metal box.

I have had the receiver beside the PC without any problems but depends on your rf environment. You won't know what interference, if any, until you look at the band.

Regards Carl

 

[gabrielxp46]

Do you have a pdf or video that best explains your hydrogen radio telescope project?

[Carl Reade]

12 hours ago, gabrielxp46 said:

Do you have a pdf or video that best explains your hydrogen radio telescope project?

Have a look at this link from the PARAC site.

http://parac.eu/projectmk3.htm

[gabrielxp46]

What is the material of the horn feed? Could it be zinc?

[Carl Reade]

On 10/08/2020 at 17:37, gabrielxp46 said:

What is the material of the horn feed? Could it be zinc?

Can be a any type of metal, but needs to be weather resistant.

[gabrielxp46]

Where do I get the measures to make the feee horn?

[gabrielxp46]

Hello?

[Victor Boesen]

Hello everyone! I've just gotten into H-line observing, and I'm writing my own software, which I will eventually use to map the Milky way. I have successfully managed to read samples from my RTL-SDR and process them into a chart. To my surprise it worked as it should, but I need to correct the noise figure from the SDR, eg. roll off and etc.

Here's a plot of the H-line in Cygnus created with my own software. As you can see the artifacts from the SDR are quite annoying, and ideally I'd like a perfectly flat spectrum.

I've been reading through some of @Coto's source code from PICTOR, but I can't quite understand the code used to produce his "Calibrated spectrum" plot:
https://github.com/0xCoto/PICTOR/blob/b83c2c0d1eb486d82cc20154d0c69dc9e2f7d13c/plot_hi.py#L36

I hope someone, perhaps even Coto himself, can help me solving or explaining the code behind the "mask" in the code example above.

My own code is still very much WIP, but can be found here:
https://github.com/byggemandboesen/H-line-software

Thanks in advance and happy new year!

EDIT: I've also looked at this link, although I find this way of calibrating the spectrum from an "empty" part of the milky way to be a little non-scientific?

Edited December 31, 2020 by Victor Boesen

[Ed astro]

Hi Victor,

When I do hydrogen line observations, I use the frequency switching method to get rid of the SDR artifacts. After taking a hydrogen line spectrum I shift the frequency by about 2 MHz to get a "dark" spectrum. The hydrogen line spectrum is then divided by the frequency switched spectrum. It is not an ideal method, but it works good enough for the hydrogen line because the hydrogen line is a relatively strong signal. There are also other methods of obtaining a dark spectrum, such as covering the antenna with RF absorbing material or pointing the antenna to the ground.

Whatever method you choose, the spectrum will often have a residual slope. You can then fit a line through the parts of the spectrum which do not contain the hydrogen line signal, and divide the.

6 hours ago, Victor Boesen said:

EDIT: I've also looked at this link, although I find this way of calibrating the spectrum from an "empty" part of the milky way to be a little non-scientific?

Using an "empty" part of the sky is indeed not a very good method (at least not for hydrigen line), because the hydrogen line is literally everywhere. 

I think the "mask" in the Virgo code is used to define where the standard deviation of the noise in the spectrum (for calculating the signal to noise ratio) is calculated. This has to be done in the parts of the spectrum away from the hydrogen line, so the mask defines which parts of the spectrum should not contain any hydrogen line signal. 

[Carl Reade]

Another way would be to feed the system with a dummy load instead of the antenna for a period of time while recording. Straight into the LNA then reconnect the antenna feed.

Carl

[Victor Boesen]

7 hours ago, Ed astro said:

Hi Victor,

When I do hydrogen line observations, I use the frequency switching method to get rid of the SDR artifacts. After taking a hydrogen line spectrum I shift the frequency by about 2 MHz to get a "dark" spectrum. The hydrogen line spectrum is then divided by the frequency switched spectrum. It is not an ideal method, but it works good enough for the hydrogen line because the hydrogen line is a relatively strong signal. There are also other methods of obtaining a dark spectrum, such as covering the antenna with RF absorbing material or pointing the antenna to the ground.

This is a very easy yet clever solution!! Thank you very much:)

Thanks to you Carl as well!

[robin_astro]

15 hours ago, Carl Reade said:

Another way would be to feed the system with a dummy load instead of the antenna for a period of time while recording. Straight into the LNA then reconnect the antenna feed.

Carl

A "Dicke switch"

With a low noise dummy load and a noise source you could correct both for noise floor/spurii  and receiver gain/spectral response (rather analogous  to darks and flats in imaging)

Robin

Edited January 1, 2021 by robin_astro

[robin_astro]

17 hours ago, Ed astro said:

pointing the antenna to the ground.

 

Doesn't this give a strong thermal signal? It does at 12 GHz

http://www.threehillsobservatory.co.uk/astro/radio_astronomy/radio_astronomy_1.htm

or is it insignificant compared with galactic hydrogen ?

Cheers

Robin

Edited January 1, 2021 by robin_astro
example added

[Ed astro]

2 hours ago, robin_astro said:

Doesn't this give a strong thermal signal?

Yes it does. Putting RF absorbing material in front of the antenna or even using a dummy load will give al ot of thermal noise as well. I tried some of these methods out a few years ago, when I was doing my first hydrogen line observations. Even with the thermal noise they still work, because the thermal noise is broadband while the hydrogen line is not. However, the spectrum was not quite as flat as when frequency or position switching were used.

 

[Victor Boesen]

Thanks to @Ed astro for the simple solution of just collecting an "empty" sample at a slightly higher or lower frequency I had some time today to brush up my software. I think it turned out nice, but I have some issues to fix when averaging a large number of FFT's and the y-axis which doesn't really contain any useful information as of now.

Here are two images of the hydrogen line between Cygnus and Cassiopeia and one in from around Deneb in Cygnus. I believe I managed to catch two peaks in the first photo(maybe even three but the resolution isn't high enough to confirm I'd say).

Thanks all!

Victor

[Carl Reade]

On 02/01/2021 at 16:46, Victor Boesen said:

Thanks to @Ed astro for the simple solution of just collecting an "empty" sample at a slightly higher or lower frequency I had some time today to brush up my software. I think it turned out nice, but I have some issues to fix when averaging a large number of FFT's and the y-axis which doesn't really contain any useful information as of now.

Here are two images of the hydrogen line between Cygnus and Cassiopeia and one in from around Deneb in Cygnus. I believe I managed to catch two peaks in the first photo(maybe even three but the resolution isn't high enough to confirm I'd say).

Thanks all!

Victor

Yes there are three peaks in there here's what I got a while back. Working well!!