Re: [SARA] methanol maser detection with a small dish

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Michiel Klaassen

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Feb 23, 2021, 9:56:19 AM2/23/21
to camras-forum, Eduard Mol
Hallo Allen,
Hierbij de post die op SARA is geplaatst door Eduard Mol; hij heeft de maser WH(OH) gedetecteerd op 12GHz.
En dit heeft hij gedaan met een 1 meter !! schotel; dit is fantastisch. Ik heb hem natuurlijk gefeliciteerd met dit resultaat.
Je kan de curve vergelijken met die van mijn project 23.
groeten,
Michiel

Op ma 22 feb. 2021 om 19:35 schreef Eduard Mol <eddiem...@gmail.com>:
Hi all,

Over the past few months my father and I have been working on a small radiotelescope for centimetre wavelengths. I was interested in observing methanol and water masers at 12 and 22 GHz, but the mesh surface of my 3 metre dish is not  good enough for such high frequencies. Moreover, pointing and tracking by hand is very difficult at such high frequencies. Therefore, I decided to buy a smaller solid offset dish which was light enough for my HEQ5 equatorial mount. this solves at least most of the tracking and pointing problems. However, the dish has a diameter of only 1 metre, so its surface area is 9X smaller than that of a 3 metre dish. 

I decided to start working on the 12,178 GHz methanol line first. In an earlier thread on this forum (https://groups.google.com/g/sara-list/c/9OW8LU9LGvU) Michiel Klaassen and Wolfgang Herrmann pointed out to me that detecting water and methanol masers should be possible with a 3 metre dish. They also mentioned that 12 GHz methanol was easier on the receiver side because LNBs for this frequency range are widely available. 
W3(OH) should be one of the brightest methanol masers in the northern sky, Blaszkiewicz el al. (2004) mentioned a flux density of 793 Jansky. I calculated that with my 1 metre dish and an aperture efficiency of 0.5, an ~800 Jy source should give an antenna temperature of 0.1 kelvin. I tried to calculate the minimum integration time needed to detect W3(OH) using the radiometer equation. With a Tsys of 100 kelvin, an aperture efficiency of 0.5 and a bandwidth of 10 KHz I would need about an hour to detect a 0.1 K difference with an SNR of 5. Of course, this is the theoretical minimum integration time, so it might be much harder in reality. However, I decided that this was still worth giving a try.

I used an inverto Ku band single PLL LNB to downconvert the 12 GHz signal to L-band. the LNB has 2 local oscillators, I needed to switch on the high band 10.6 GHz LO, This is done by inserting 22 KHz tone. My father built a special power supply which delivers 12V DC with the 22 KHz tone superimposed, this is fed into the LNB via a bias tee. I tested how much the LO frequency drifts and found that it only drifted about 10- 15 KHz in a few hours. this is much less than the width of the maser line, so I decided it was not necessary to modify the LNB for higher stability. 

On the evenings of february 20 and 21, I tried to detect the methanol maser of W3(OH). Integration time was 2 hours on the first evening and 3 hours on the second. I also measured the Astra 3B beacon again after the observations to measure the frequency offset of the LO. On both evenings I detected a weak 0.1K signal at around -45.5 km/s. It looks quite convincing but I first want to make sure it is not some weird form of RFI.
W3OH12ghzfeb.png
To be continued....

Eduard Mol

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Hans Smit

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Feb 24, 2021, 8:58:52 AM2/24/21
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Hallo Michiel,
Mooie resultaten van jou en Eduard Mol. Een aansporing om dat ook (nog eens) te proberen. Eerdere poging leverde niets op. 

Afgelopen maanden ben ik druk bezig geweest om de verticale beweging van mijn telescoop te repareren Ingedrongen regenwater had de boel grondig verwoest. 
Hans


Op 23 feb. 2021 om 3:56 PM heeft Michiel Klaassen <vmin...@gmail.com> het volgende geschreven:


Hallo Allen,
Hierbij de post die op SARA is geplaatst door Eduard Mol; hij heeft de maser WH(OH) gedetecteerd op 12GHz.
En dit heeft hij gedaan met een 1 meter !! schotel; dit is fantastisch. Ik heb hem natuurlijk gefeliciteerd met dit resultaat.
Je kan de curve vergelijken met die van mijn project 23.
groeten,
Michiel

Op ma 22 feb. 2021 om 19:35 schreef Eduard Mol <eddiem...@gmail.com>:
Hi all,

Over the past few months my father and I have been working on a small radiotelescope for centimetre wavelengths. I was interested in observing methanol and water masers at 12 and 22 GHz, but the mesh surface of my 3 metre dish is not  good enough for such high frequencies. Moreover, pointing and tracking by hand is very difficult at such high frequencies. Therefore, I decided to buy a smaller solid offset dish which was light enough for my HEQ5 equatorial mount. this solves at least most of the tracking and pointing problems. However, the dish has a diameter of only 1 metre, so its surface area is 9X smaller than that of a 3 metre dish. 

I decided to start working on the 12,178 GHz methanol line first. In an earlier thread on this forum (https://groups.google.com/g/sara-list/c/9OW8LU9LGvU) Michiel Klaassen and Wolfgang Herrmann pointed out to me that detecting water and methanol masers should be possible with a 3 metre dish. They also mentioned that 12 GHz methanol was easier on the receiver side because LNBs for this frequency range are widely available. 
W3(OH) should be one of the brightest methanol masers in the northern sky, Blaszkiewicz el al. (2004) mentioned a flux density of 793 Jansky. I calculated that with my 1 metre dish and an aperture efficiency of 0.5, an ~800 Jy source should give an antenna temperature of 0.1 kelvin. I tried to calculate the minimum integration time needed to detect W3(OH) using the radiometer equation. With a Tsys of 100 kelvin, an aperture efficiency of 0.5 and a bandwidth of 10 KHz I would need about an hour to detect a 0.1 K difference with an SNR of 5. Of course, this is the theoretical minimum integration time, so it might be much harder in reality. However, I decided that this was still worth giving a try.

I used an inverto Ku band single PLL LNB to downconvert the 12 GHz signal to L-band. the LNB has 2 local oscillators, I needed to switch on the high band 10.6 GHz LO, This is done by inserting 22 KHz tone. My father built a special power supply which delivers 12V DC with the 22 KHz tone superimposed, this is fed into the LNB via a bias tee. I tested how much the LO frequency drifts and found that it only drifted about 10- 15 KHz in a few hours. this is much less than the width of the maser line, so I decided it was not necessary to modify the LNB for higher stability. 

On the evenings of february 20 and 21, I tried to detect the methanol maser of W3(OH). Integration time was 2 hours on the first evening and 3 hours on the second. I also measured the Astra 3B beacon again after the observations to measure the frequency offset of the LO. On both evenings I detected a weak 0.1K signal at around -45.5 km/s. It looks quite convincing but I first want to make sure it is not some weird form of RFI.
<W3OH12ghzfeb.png>

To be continued....

Eduard Mol

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Michiel Klaassen

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Feb 24, 2021, 11:10:49 AM2/24/21
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Hallo Hans,

Inderdaad; ik had al uitgerekend dat jij met je 3m schotel de maser ook zou moeten kunnen detecteren.
Vandaar dat ik je een 12GHz LNB opgestuurd had. Hopelijk lukt het deze keer.

Misschien ken je JJ; F1EHN, hem heb ik destijds ook benaderd om een proef te doen met deze LNB. 
Echter hij wilde geen tijd vrijmaken voor een proef; hij was continu bezig met een serie van contesten.

Zo heeft ieder zijn keuze; ik heb een certificaat van W3(OH) aan mijn muur hangen in de control container in PT.

Groeten,

Michiel


Op wo 24 feb. 2021 om 13:58 schreef Hans Smit <smit...@gmail.com>:
Message has been deleted

Hans Smit

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Aug 30, 2022, 9:21:39 AM8/30/22
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Op 24 feb. 2021 om 5:10 PM heeft Michiel Klaassen <vmin...@gmail.com> het volgende geschreven:



Hans Smit

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Aug 30, 2022, 1:55:01 PM8/30/22
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Hallo Michiel,
Ik heb een aantal keren geprobeerd om jouw metingen (met de gekregen LNB) te herhalen.
Voor deze metingen  had ik de LNB met een piepschuim verloop ring in mijn 1420 MHz front end geklemd. Mijn Airspy ontvanger had ik voorzien van een rubidium klok, (hiervan was overigens  geen invloed merkbaar)

Jouw metingen aan “de”pulsar en de methanol maser zijn een mooie prestatie. Er ligt voor mij nog een groot on-ontgonnen terrein te wachten. Ik verwacht de komende tijd veel van mijn achterstand te kunnen wegwerken. Ik verwacht wel dat hierbij veel problemen zullen opdoemen.

Helaas heb ik deze zomer grotendeels  moeten  besteden met het verplaatsen van een schutting en de er bij behoren beplanting (e.a. door een kadaster meting). Door al dat gesleep zit ik nu met een hernia en staan mijn activiteiten op een laag pitje.

De bomen rondom mijn telescoop nemen steeds meer gezichtsveld weg. Om te controleren of mijn waarnemingen mogelijk bomenruis bevatten heb ik een cameraatje op de telescoop gemonteerd. Ik kan nu zien wanneer een boom in de de weg staat of komt te staan.

Vriendelijke groeten,
Hans Smit.
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