22.2GHz LNA / LNB for Water Maser Detection

[S.D. Holland]

Greetings!  

        This is my first post here, so sorry if this topic has already been discussed.  My question is - what LNA / LNB are being used for Water Maser detections and measurements?  I am aware of the Norsat 9000LDF, but am wonder if there are others.

Thanks,

Doug

[Adrian]

 Hi Doug,

  I'm also interested in the Water MASER 22GHz reception and have also been exploring what LNBs are available for this besides the Norsat and the only other commercial  LNB I've found for that frequency are Chinese LNB's that spec for the 21.20 - 22.20 GHz range.  These price is roughly about the same ~$180 from Alibaba vs the online price ~$194 for the Norsat 9000 LDF ones but unfortunately Alibaba require a minimum purchase of 2 which is why I haven't splurged on a purchase. Both Norsat and these LNB's are DRO L.O.'s so their stability is also an issue. I don't know of anyone using them for the H2O MASER work so I'd be curious if anyone here has had any experience with them. Not sure if the site here allows for external links but anyway  the Alibaba link is :

https://www.alibaba.com/product-detail/Ka-Band-DRO-LNB-21-20_1601090335179.html?spm=a2700.shop_plser.41413.23.2913723dBbRDOY

 If you have any additional info for the 22GHz reception I would also appreciate an update post..

Adrian 

[S.D. Holland]

Adrian,

        Thank you for the information.  I had not found the Alibaba one.  I am just starting to think about this, but am interested.  The postings I have seen from three different people having success detecting the water masers are all using the 9000 LDF.  Will let you know if I find any other options.

Thanks again,

Doug

[Eduard Mol]

Hi,

I guess I am the water maser guy here so I can share some of my experience…

I use a norsat 9000LD unit for water maser observations, have not used any of those chinesium units so I can’t tell how good or bad they are in terms of noise figure and LO stability. The LO stability of those DRO LNBs can indeed be an issue indeed but there are ways to deal with it. 

You can use a DRO LNB “as is” for water maser detection, in that case your sensitivity will be degraded and you have a large uncertainty in the frequency but it’s still possible to detect the strongest sources. 

One trick to deal with LO frequency drifting over long integration times is to use a stable reference signal (be sure to offset it by a couple MHz so it does not overlap with the maser!). Then you can do the frequency correction afterwards in the data processing. I have used the weak 28th harmonic of a Leo Bodnar GPSDO for the reference.

Michiel Klaasen had some success using an NTC heater to control the temperature of the LO to minimise frequency drifting (which apparently is mainly caused by temperature changes). He also uses a reference signal for frequency calibration (see 

http://parac.eu/projectmk27.htm)

It is probably even better to get rid of the DRO entirely and somehow lock the LO to an external reference, at Astropeiler they did something like that if I remember correctly. It is well beyond my expertise though so I have not done any such modifications.

If you want to know more there is an article describing my 22.2GHz setup in the August 2022 SARA journal. There is also a long thread here on the SARA forum documenting the building and first observation results of my water maser setup, see https://groups.google.com/g/sara-list/c/TrZR8yCIWUE/m/3DNdYneJBwAJ.

 

Op di 14 jan 2025 om 14:28 schreef Adrian <kjan...@gmail.com>

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[Marcus D. Leech]

On 14/01/2025 13:38, Eduard Mol wrote:

Hi,

I guess I am the water maser guy here so I can share some of my experience…

I use a norsat 9000LD unit for water maser observations, have not used any of those chinesium units so I can’t tell how good or bad they are in terms of noise figure and LO stability. The LO stability of those DRO LNBs can indeed be an issue indeed but there are ways to deal with it. 

You can use a DRO LNB “as is” for water maser detection, in that case your sensitivity will be degraded and you have a large uncertainty in the frequency but it’s still possible to detect the strongest sources. 

One trick to deal with LO frequency drifting over long integration times is to use a stable reference signal (be sure to offset it by a couple MHz so it does not overlap with the maser!). Then you can do the frequency correction afterwards in the data processing. I have used the weak 28th harmonic of a Leo Bodnar GPSDO for the reference.

Michiel Klaasen had some success using an NTC heater to control the temperature of the LO to minimise frequency drifting (which apparently is mainly caused by temperature changes). He also uses a reference signal for frequency calibration (see 

http://parac.eu/projectmk27.htm)

It is probably even better to get rid of the DRO entirely and somehow lock the LO to an external reference, at Astropeiler they did something like that if I remember correctly. It is well beyond my expertise though so I have not done any such modifications.

If you want to know more there is an article describing my 22.2GHz setup in the August 2022 SARA journal. There is also a long thread here on the SARA forum documenting the building and first observation results of my water maser setup, see https://groups.google.com/g/sara-list/c/TrZR8yCIWUE/m/3DNdYneJBwAJ.

I'll note that Orbital Research do 22GHz-band LNBs, mostly on a semi-custom basis.  The owner and CEO is an old
  friend of mine:


https://orbitalresearch.net/

They have PLL-based LNBs that can be referenced to an external oscillator (10MHz).

They won't be cheap, unfortunately.

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[Doug Holland]

Eduard,

       Thank you for the reply.  I have been following your success on the SARA RTOPs.  That is what got me started thinking about water masers.  Keep up the great work!

Thanks,

Doug

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.

[James Morris]

See if you can find an SPC Ka-Band PLL LNB with external reference. They are not common but seem to pop up at times.

Note that they are specified for up to 21.2 GHz and I don't know yet how well they perform at 22 GHz.

James W7TXT

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[fasleitung3]

We are using a LNB from Inverto: https://www.inverto.tv/lnb/208/kaku-co-locate-linear-23mm-lnb-with-one-kaku-switchable-output-and-one-ka-output?locale=en

However, it seems that this is no longer available. Also, we have done a major modification: The Ku band section is PLL-based so we are injecting a 25 MHz reference signal. The Ka band section has a DRO based oscillator at ~ 10.125 GHz which is frequency doubled as LO. Here we have replaced this with a PLL-based oscillator at 3.375 GHz which is frequency tripled to replace the original 10.125 GHz singal. All this is referenced to our observatory master clock.

Of course on can try it without the modification. But as mentioned I do not know where to get one at the moment.

Wolfgang

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[James Morris]

FYI, I posted some initial test results for this LNB here:

https://social.kernel.org/notice/Ac3eWRlirgKRzORTeK

It does cover the maser frequency, although the NF performance there is not yet known.

James W7TXT

[Marcus D. Leech]

On 20/01/2025 15:26, James Morris wrote:

FYI, I posted some initial test results for this LNB here:

https://social.kernel.org/notice/Ac3eWRlirgKRzORTeK

It does cover the maser frequency, although the NF performance there is not yet known.

James W7TXT

I did something similar with one of those "Inverto" LNBs a few years ago.  I stuck a HSMS-series mixer diode in the bottom of
  a piece of 1/2" type-L copper tube.  Excited the diode with a 4GHz (AFAIR) signal to look at the 5th harmonic.  I was able to
  see the correct IF output, but, like you, I had no way of characterizing the effective noise figure of the LNB outside its usual
  pass-band.  Other LNBs that I've pulled apart have very little filtering at RF, other than that implied by the waveguide
  in the LNB/LNBF.

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