mm-wave amateur radio astronomy?

[WarinSpace Game]

Hey all,

What would be the easiest radio source or spectral line detectable at >=30 GHz? I'd like to build a millimeter wave telescope, so I'd like to see what apertures would be needed to make a detection (other than the Sun obviously).

[fasle...@googlemail.com]

Above 30 GHz the Methanol masers at around 37 GHz are probably the easiest. See https://iopscience.iop.org/article/10.1088/0004-637X/742/2/109/pdf  for a list.

If you are ok with somewhat lower frequencies, then the 22 GHz water masers are quite bright.

Wolfgang

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[Eduard]

Hi,

Has any amateur succeeded in detecting 22 GHz water masers? 

Water masers are indeed quite bright and variable, and I have thought about making a small radiotelescope for 22 GHz. However, there seemed to be just too many problems and difficulties. The very short wavelength means that the dish surface needs to be very accurate, and large, high-quality dishes are very expensive. Another problem would be atmospheric attenuation caused by water vapour in our atmosphere. I could not find any downconverters or LNBs for 22 GHz (at least not any that cost less than $1500) and making a downconverter myself would be too difficult for me. 

Best regards,

Eduard

Op do 19 mrt. 2020 22:17 schreef fasleitung3 via Society of Amateur Radio Astronomers <sara...@googlegroups.com>:

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[Michiel Klaassen]

Hi,

Contrary to H1, which you cannot miss when pointing your telescope, higher frequencies are emitted from almost point sources. So the pointing has to be very accurate.

You can start also on lower frequencies like 12GHz. You can start with a commercial LNB like this one:

https://www.ebay.com/b/Avenger-TV-Satellite-LNB-Downconverters/149971/bn_724682

You can find more info when you search for "12GHz maser" on this forum or else here

http://parac.eu/projectmk23.htm

I know that Wolfgang and his team detected a water maser; search this forum.

We also detected the 22GHz maser but the result is not suitable for publication (yet). 

regards

Michiel

parac.eu

Op vr 20 mrt. 2020 om 07:57 schreef Eduard <eddiem...@gmail.com>:

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[Eduard]

Hi Michiel,

Accurate pointing is not an issue. I have a HEQ5 telescope mount which I use for astrophotography, and using it to point a dish instead of a "normal" telescope is not a problem as long as the dish is not too large or heavy. 

I know the 12 GHz methanol masers, but the problem is they are quite weak (only a few hundred Jy) and I do not have a 9 metre dish in my backyard... ; ) The 6,7 GHz masers seem to be much brighter, but again there are no downconverters/ LNB for that frequency.

Best regards, 

Eduard

Op vr 20 mrt. 2020 11:16 schreef Michiel Klaassen <vmin...@gmail.com>:

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[fasle...@googlemail.com]

Eduard,

Indeed we have observed water maser emission at 22 GHz from various sources. Please find attached an example of one of the stronger sources, W51. The horizontal scale is the VLSR-corrected velocity and the frequency in MHz. The vertical scale is the flux in uncalibrated units.

This observation was made with our 10-m dish and two minutes integration time. The signal to rms noise is 107, so quite good. If one extrapolates this to a 3-m dish, about 250 minutes integration time would be needed to get the same SNR. However, one can certainly live with less SNR. So I thing it is doable to observe water masers with a smaller dish. Since water masers can vary, W51 may not be the strongest source at the moment, so one should try others as well. I should also mention that at 22 GHz or 10-m dish is under-illuminated so the effective area is actually smaller so it may even look better for the 3-m dish.

The tricky thing is the receiver. In our case it was a dual Ku/Ka band LNB. It was modified so that an external reference frequency could be used to get precise frequencies. Whether one can do without that and just live with the fact that there is a frequency offset, I don’t know. I will need to check with Horst (our high frequency expert) which Ku/Ka LNB he was using.

 

Easier on the receiver side there is Methanol at 12 GHz where one can use a standard LNB. As you pointed out these masers are weaker than the water masers. I have attached an example of the Methanol maser in W3. This is with 10 minutes integration time and a SNR of 41. Extrapolating this to a dish of 3 meter leads to an integration time of ~1230 minutes. But then one could also reduce the spectral resolution and reduce the requirement for the SNR. Reducing the spectral resolution by a factor of 4 (which is still quite ok) reduces the observation time by half, and going from 41 to about 10 for SNR cuts the required integration time by a factor of 16. Then you only need some 20 minutes for a detectable signal.

 

So in conclusion I would say that both water masers and methanol masers are within the realm of possibilities for a 3-m dish. Obviously it is not easy-going on the receiver side.

Best,

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[Doug Ronald]

I can help with the dish end of this potential project. I have three commercial 26 GHz, about four foot diameter, linear polarization feed, terminated with an SMA female connector, dishes. The SMA launcher may be removed to expose a WR34 flange where an LNA would be mounted. Contact me off-list for further details if interested. I am in the San Francisco Bay area.

Doug, W6DSR

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[Eduard]

Hi Doug,

Thank you very much for your offer. Unfortunately there is an ocean and a continent between my town and the San Francisco bay area ; )

Best regards,

Eduard

Op di 24 mrt. 2020 22:51 schreef Doug Ronald <do...@dougronald.com>:

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[Doug Ronald]

Yes, I figured as much, but I have had some inquiries about the antenna where at least one is only a continent away…

Good luck with your efforts,

-Doug, W6DSR

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