Ed astro

Hi all,

More observations have been done at 22.2 GHz over the past two weeks. I have pointed the dish at a number of different sources: NGC 2071, NGC 7129, W75, Cepheus A, IRAS 06053-0622 and G25.8-0.18. Unfortunately, none of these sources were detected, they are probably too weak right now for detection with a small 1 metre dish. 

W49 and W51 were successfully observed again. It seems like both sources have become weaker since the first observations 5- 6 weeks ago. However, since the vertical axis is not calibrated it is hard to tell which part of the change is real, and what part is due to pointing errors or gain variations. On the other hand, the different maser features (peaks) in the spectrum of a source usually vary independently of each other, while gain variations or pointing errors should influence the measured intensity of all the peaks equally. I plotted my most recent spectrum of W49 (from March 26) over an earlier spectrum made on February 12. The strongest feature has significantly decreased in intensity, while the weaker peaks have remained almost the same. It is therefore likely that the decreasing intensity of the main peak is (mostly) due to the intrinsic variability of the source.

The same was done for W51. However, W51 lacks any sufficiently strong peaks besides the main peak to compare with. 

It would be interesting to observe these sources again in one or two months.

Hi Victor,

That filtered LNA could be really handy- there is often quite a bit of RFI above 1.7 GHz which can cause some problems when trying to detect weak signals. What is the noise figure of your LNA? Low system noise is really important for this kind of work.

I have detected four OH masers with my 3 metre dish over the past few years: these were the red giant stars NML Cygni, OH26.5+0.6 and V669 Cas at 1612 MHz, and  the star forming region W3(OH) at 1665 MHz. I used a G8FEK LNA and homemade filters for 1612 and 1665 MHz. These observations were quite challenging, it required tens of minutes to several hours of data recording to get good results. 

Hi Victor,

On 09/03/2022 at 21:49, Victor Boesen said:

Thank you Ed, very useful!

I don't think I'll be done with hydrogen line in the near future, but would also like to play with new stuff. I just started on university the summer last year and have yet to play with the 3m dish available on campus 

Should be nice for hydrogen line, although for higher frequencies in X-band, Ku, K band and etc there are also a couple of solid 1m dishes available.

Plenty to observe out there!!

Victor

These look like some really nice dishes to play around with!

As mentioned before water masers are difficult to observe due to their high frequency (you need really accurate pointing and tracking) but there are other options at lower frequencies as well. OH (hydroxyl) has four maser lines at 1612, 1665, 1667 and 1720 MHz. These frequencies are quite close to the hydrogen line, so you could use the same SDR receiver and LNA, and probably even the same feed that you use for hydrogen line observations if it performs well enough at 1.6 GHz. OH masers are generally a lot weaker than water masers though, but with a 3 metre dish you should be able to detect a few of them.

Hi Victor,

I am using the SDR# IF average plugin for averaging the spectrum over a longer time period.

The methods for making spectra of these masers are very similar to hydrogen line observing- you can use the same software and observation routine. The main difference is that the maser lines are usually 10- 100 times weaker, so you need to integrate a lot longer to get good SNR. Typically I make  tens of spectra with each an integration time of a few minutes, and average them all afterwards. I keep the resolution low at 256 bins (12 KHz for an SDR with a bandwidth of 3 MHz, just enough to resolve the lines while keeping the noise low.

Observing these water masers is challenging but also rewarding, they are bright and variable radio sources but they are rarely observed by amateurs. So if you are done with hydrogen line observing at some point this might be an interesting project.

Well Marv that is mostly my fault since I did not even really try to explain this 😉 

What you are seeing are spectra of water masers. When water molecules in a gas cloud are subjected to strong infrared radiation or collisions with other molecules, they can emit strong microwave radiation at a frequency of 22235 MHz (wavelength of about 13.5 millimeters.) These conditions are usually found inside star forming regions. When we point a radio telescope at a star forming region and plot the intensity of the received microwave radiation against frequency, we see a spike at or near 22235 MHz. Due to Doppler shift, this spike is usually a few MHz above or below the rest frequency depending on how fast the source is moving towards or away from us. In many cases we see a number of different spikes in the spectrum, these all correspond to different sources within the same star forming region, which are moving at different velocities.

I hope this makes things a bit more clear!

Best regards,

Eduard

Hi Kevin,

The whole dish setup (including the counterweight, the LNB and the supports) is about 10 kg, so it is a bit on the heavy side but it should still be well within the limits of the mount. So far I have not had any problems with the 1 metre dish mounted on the HEQ5.

It does catch a lot of wind though, so it can only be set up with calm weather.
 

Hi all,

Last weekend I observed two more 22.2 GHz water maser sources in star forming regions.

The first one was W3. This star forming region is associated with the bright nebula NGC 896 in Cassiopeia. The protostars themselves are completely obscured by thick clouds of dust and gas, and are therefore  invisible with "regular" visible-light telescopes. With a radio telescope we can detect the maser sources associated with these young stars, because the radio waves easily pass through the dust clouds. 

Just like during the observations last week I pointed the dish 1 degree away from the target twice during the observation to check whether the signal was indeed coming from the direction of the target source.

The other source is Orion KL (the Kleinmann- Low nebula). This is one of the closest star forming regions, it is embedded inside the well- known Orion nebula. Orion KL was much lower in the sky than W3 at my location (about 30 degrees), and because of this there was more absorbtion and thermal noise from water vapour in the atmosphere. Despite these issues the water maser was still succesfully detected. Besides the main peak at 22229.8 MHz there are several weaker lines in the spectrum as well.

best regards,

Eduard

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.

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

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

Hi all

After the successful detection of two methanol masers at 12.2 GHz with my 1 metre dish I wondered whether it was possible to detect water masers at 22.2 GHz as well. Recently I did my first successful observations. The setup I am using is broadly similar to what I used to detect the 12.2 GHz methanol line: a 1 metre dish on a HEQ5 mount, with an LNB placed in the focal point which amplifies the incoming signal and converts it down to a lower frequency within the range of my SDR receiver. The main difference is in the LNB: I am using a norsat 9000LDF to receive at 22.2 GHz. It has an LO frequency of 20250 MHz so the water line is mixed down to 22235-20250=1985 MHz. This is unfortunately just outside the tuning range of my airspy mini SDR so I am using a NeSDR XTR instead, which has an extended tuning range up to 2300 MHz. Since the norsat LNB came without a feed I made my own rectangular horn feed from a sheet of brass foil. It was designed using the HDL-ANT program by W1GHZ; the length of the horn is 25mm, the dimensions of the opening are 24X20mm.

Last weekend I did my first successful observation of W49, one of the strongest water maser sources in the sky. The Arcetri catalog of H2O maser sources by Valdettaro et al. (2001) reports a peak flux density of 31000 jansky, making W49 one of the brightest objects in the sky at microwave frequencies! However, like many other water masers W49 is highly variable on timescales of months to years. Flux density values published years ago should therefore be taken with some caution. During the observation of W49 spectra were recorded at 5 minute intervals for about 1.5 hours. A heatmap of all the 5- minute spectra is shown below:

The dish was pointed 1 degree away from the target twice during the observation, this was done in order to check whether or not a received signal was coming from the direction of W49. The narrow signal at 22234.9 MHz is an artifact of the SDR. The strong signal at 22235.75 MHz disappeared when the dish was pointed “off-target”, so it is most likely coming from the direction of W49. There is some frequency drifting, this is because the LO frequency of the LNB is unfortunately not very stable. After averaging all the on-target spectra, some weaker peaks could be seen as well. I did not convert frequency to radial velocity because the LNB LO frequency is still rather uncertain.

Finally, the star forming region W51 was also observed. In October of last year, a strong flare of the H2O maser in this star forming region was reported (see ATel #15002: https://www.astronomerstelegram.org/?read=15002). The signal was indeed quite strong, even stronger than W49. Maybe the flare is still ongoing. However, I have no way to determine the flux density of the maser at the moment so this is just speculation.

Anyway, this is pretty much all I have to say about this project right now. This post has become way too long but I hope you all don’t mind 😉

Eduard

Hi all,

It has been a while since I posted in this topic. I was hoping that I could detect more methanol maser sources, but unfortunately most of the sources are much weaker than W3(OH) and G188. There was an unsuccessful attempt to detect the variable source G9.62+0.19 last November, it was rather low above the horizon and my dish was picking up too much thermal noise from the ground and from nearby trees. 

I did make a new observation of W3(OH) in September, this time by pointing the dish at the declination of W3(OH) and letting the source drift through the beam as the Earth rotates. Because the beam of my 1 metre dish is only two degrees wide at 12 GHz, the duration of the transit was less than 15 minutes. This is not much time to observe such a weak signal, so a good signal-to-noise ratio was not expected. However, the methanol maser line was still detected. This demonstrates that W3(OH) could be observed without a tracking mount. By repeating the transit scan multiple times and averaging the results it should be possible to build up more integration time and achieve a higher signal-to-noise ratio.

Hi Lucas, 

yes this looks fairly normal. The three bumps in the graph are an artifact of the SDR and will always be there no matter where you point your antenna. 

The hydrogen line is centered at 1420.406 MHz, and you can usually detect it between 1420 and 1421 MHz (the frequency can vary somewhat due to doppler shift). Your graph spans from 1418.1 to 1420.2 MHz, these frequencies are a bit too low and you will likely have missed the hydrogen line.

Could you shortly describe the setup you are using and/ or post an image of your setup?

Best regards,

Eduard

5 hours ago, Victor Boesen said:

Quite a drive I must admit... In any case, I don't think my mom would agree to pick up such a large dish It looks really good though, and there are a lot of useful scenarios where it comes in handy! Out of curiosity, have you tried playing around with software defined radios with these dishes? With the large ones you could probably receive the geostationary satellit GOES-13 or even X-band low earth orbit one's with a resolution of 250m/px! The list goes on:)

Yep these dishes would indeed be great for amateur radio or radio astronomy! Such solid dishes would not only be useful for "regular" 21 cm work but also work well at cm wavelengths (unlike mesh dishes). These could for example be used for detecting and monitoring methanol masers at 6.7GHz or 12GHz, or maybe even water masers at 22GHz if the quality of the dish is good. Indeed one can make a very long list of interesting stuff to do with a large dish. 

Hi Peter,

I would have expected to see atleast something at this point...

The '"wavy" response is also a bit strange, but it may just be the passband respons of the SDR you are using.

To get an idea of what you should be able to see I quickly put together something similar to your setup. I used a small conical horn antenna (which whas originally intended as a feed antenna for my dish but was rarely used), a nooelec sawbird HI LNA and an RTL SDR. I did not do bandpass correction. The hydrogen line shows up as a small bump in the spectrum that normally would not be there. Note that the aperture of my horn antenna is probably quite a bit smaller than yours, so you should expect to see a somewhat stronger HI signal than me.

Hi Peter,

I see your vertical scale goes from -34 to -174 dB, so you probably would not see a 1 or 2 dB H line signal.

You can use the "gain" and "level" sliders to zoom in on the vertical scale. I usually set "gain" to maximum and adjust the "level" until I have a good view of the spectrum.

Hi,

I agree with Carl Reade, with my 3 metre dish the hydrogen line is at most around 2dB above the noise floor. I also use IF average and it works fine for me.

I would like to add that the sun may not be a particularly strong noise source given the relatively small aperture of your horn antenna. It may be easier to use the thermal noise from the ground to get an idea of the sensitivity of your setup. If you point the antenna to the ground you should see an increase in noise of more than 3 dB. If it is less than 2 dB seeing HI will be really hard. 

Hi,

The probe length should be a bit less than 1/4 wavelength. In my 1420 MHz feed it is about 4.5 cm. However, I do not think the probe is the problem in your setup. If the probe is a few mm too long or too short you will notice that the antenna is less sensitive but you will probably still be able to detect HI. Besides my 1420 MHz feed I have also made a 1665 MHz feed (for OH line observations), its probe is of course a bit too short for 1420 MHz but when I use it at 1420 MHz I can still detect HI with it just fine. 

Hi Peter,

"Nothing works and nobody knows why" is a common problem when doing amateur radio adtronomy ; ) I must admit this hobby has a very steep learning curve. When I started in 2017/18 it took me nearly a year to get good results with hydrogen line observations. 

Looking at the pictures of your setup the first thing that comes to my mind is checking the conductivity of the insulation material. If it is not conductive, the horn antenna would not work. In that case you could try lining the inside of the horn with aluminium foil.

The sawbird HI LNA should have enough gain on its own as long as you do not have a very long and lossy coax cable between the LNA and the SDR receiver. There is already a 1420 MHz bandpass filter in the sawbird HI, so I think an extra filter is not necessary. Furthermore, losses between the antenna and the LNA have a lot of impact on the sensitivity of your system. It is therefore a good practice to keep the cable that connects the antenna to the LNA as short as possible. 

Best regards,

Eduard

The resolution of the 1 metre dish at 12GHz is about 2 degrees but the source is much smaller than that. So it is indeed effectively a point source.

Nice project!

Don't worry about all the wrinkles in the foil. As long as they are smaller than about 1/10th of the wavelength they would not be a problem. Since the wavelength is 21 cm a bunch of wrinkles of a few mm or even a cm high will probably have little effect.

I once have made a conical horn antenna from steel mesh with 1cm wide holes. Worked fine for detecting the hydrogen line.

1 minute ago, Ouroboros said:

I see, I think. Instead of plotting the methanol spectral line as intensity versus frequency you’re converting frequency to velocity relative to the sun’s. Is that right? 

Yes, that is indeed basically what I did. I converted the frecuency to the velocity relative to the average of the Sun and nearby stars (local standard of rest) but that is a detail.

8 hours ago, Ouroboros said:

Yes, very interesting. Maybe you explain this somewhere above but why is the horizontal axis velocity (km/s)?  I might have  expected it to be frequency (Hz).  

Hi,

I did indeed not discuss why I used velocity on the horizontal axis instead of frequency. Professional astronomers often use the LSR velocity for spectra of objects within our own galaxy, because they are often studying the motion of objects in our galaxy or in a star forming region. LSR (Local Strandard of Rest) velocity is the velocity with respect to our local area of the Milky Way.

I could of course have just used the frequency, but the frequency gradually changes due to the doppler shift caused by the Earths rotation and movement around the Sun. In that case it would not be that easy to add spectra from different days together. The easiest way to deal with this issue is to calculate radial velocity from the frequency values using the doppler formula, and then correcting for the velocity components of Earths orbit and rotation using an online LSR velocity calculator. I used Steve Olney's calculator (https://sites.google.com/view/hawkrao/hawkrao-calculators/vlsr-calculator) but there are others as well. Using LSR velocities also makes it easier to compare my own observations to those of others or to spectra published in the scientific literature.

Hi all,

Last week I tried to detect another 12.2 GHz methanol maser source known as G188.94+0.89. This object much weaker than W3(OH), so detecting it with a small dish is even more challenging. I observed this source on the evenings of March 23, 25, 27 and 29. The graph below shows the result after averaging all spectra from March 23, 25 and 29 (the spectra of March 27 were not used because these were more noisy and the signal of the maser was buried in the noise). There is a small peak at 10.9 km/s, the width of the peak is about 1.6 km/s. 

This result can be compared to the spectra taken by Michiel Klaassen in 2018 and 2019 with the 9.3 metre Sao Giao radio telescope (see http://parac.eu/projectmk22.htm). Both of Michiels spectra show that the velocity of the peak is about 10.5- 10.9 km/s, but the width is a bit different (about 1.3 km/s in 2018 and 2.5 km/s in 2019). Furthermore, the flux density (brightness) of this source also varies between 2018 and 2019. It seems that the G188.94+0.89 methanol maser is quite variable.

Best regards,

Eduard. 

Hi,

Surprisingly, the dish is not that much heavier than the 6" scope which I normally have set up on this mount. It does catch a lot of wind, so I can only use it when the weather is calm.