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Ed astro

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About Ed astro

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  1. 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.
  2. 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.
  3. 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.
  4. 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
  5. 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 spectr
  6. 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.
  7. Hi all, Here an update on this project. I have fixed some problems and mistakes in the frequency correction. In my previous post I mentioned that I measured the frequency of the Astra 3B satellite beacon after each observing session, but I did not really explain why this was important. The local oscillator (LO) frequency should be 10600 MHz, but in reality it can deviate tens of KHz from that frequency. It is possible to modify the LNB for better frequency stability, but I did not want to open up the LNB and mess around with the electronics. Instead, I decided to use a satellite beacon. T
  8. Hi all After a week of doing observations and another afternoon processing the data I finally have some nice results. The target I observed is the star forming region W3(OH). It is also a strong methanol maser: the 12.178 GHz methanol line, as well as other radio spectral lines, is amplified by stimulated emission. This is why we can detect the methanol line of W3(OH) with such a small aperture. It still is an incredibly weak signal though, compared to terrestrial signals from cellphones and other electronics... Luckily, the 12 GHz band is still fairly "radio-quiet", the only major
  9. Hi all, In recent years the hydrogen line has become a popular target for amateur (radio)astronomers. However, there are many more spectral lines in the radio spectrum, and I am very interested in detecting some of these lesser-known lines. Here I will describe my attempts at detecting the methanol (CH3OH) line at 12178.593 MHz. My homemade 3 metre dish was unfortunately not very useful for this project, because its surface is not accurate enough for such short wavelengths (the wavelength of the methanol line is only 2.5cm, much shorter than the 21 cm hydrogen line which the dish w
  10. Hi Victor, Nice spectra! If you want to check your hydrogen line measurements you can use the LAB survey HI profile search: https://www.astro.uni-bonn.de/hisurvey/euhou/LABprofile/index.php. You can fill in the galactic longitude and latitude of the spot in the sky you were observing, and the beamsize of the antenna in degrees (if you are using a dish, this is approximately 70 X wavelength / dish diameter.) Best regards, Eduard
  11. 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.
  12. 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. Whatev
  13. Well I have some experience with radio, I did my first detection of the hydrogen line two and a half years ago, in june 2018. It is always great to see more amateur astronomers working on radio astronomy/ hydrogen line detection.
  14. Hi all, Thank you all very much for the warm welcome! That dish in my avatar is indeed my radio telescope. it is a 3 metre dish which was built in december 2017 for a high school project by me and two of my friends. My father, who is a radio amateur, helped us a lot with all the electronics. I definitely would like to visit Jodrell Bank at some point. I is a very historic site for radio astronomy.
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