OH+ Maser emissions

[Marcus D. Leech]

Does anyone have any maser spectral plots, from an amateur dish, at the
OH+ maser lines at either/both of 1667/1665MHz?  I'm aware of the excellent
  Astropeiler Stockert results.

[Eduard Mol]

I have done observations of some OH sources with my 3 metre dish in the past. 

W3(OH) was the only one I derected at 1665 MHz, see attached plot. Total integration time was about 4- 5 hours. I have also done a bunch of observations together with the CAMRAS crew with their 25 metre dish, there is a SARA journal article on the results but I have to dig up when it was published.

Best regards

Eduard

Op do 18 sep 2025 om 17:11 schreef Marcus D. Leech <patchv...@gmail.com>

Does anyone have any maser spectral plots, from an amateur dish, at the
OH+ maser lines at either/both of 1667/1665MHz?  I'm aware of the excellent
   Astropeiler Stockert results.

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[Marcus D. Leech]

On 2025-09-18 12:50, Eduard Mol wrote:

I have done observations of some OH sources with my 3 metre dish in the past. 

W3(OH) was the only one I derected at 1665 MHz, see attached plot. Total integration time was about 4- 5 hours. I have also done a bunch of observations together with the CAMRAS crew with their 25 metre dish, there is a SARA journal article on the results but I have to dig up when it was published.

Best regards

Eduard

Thanks Eduard.   Do you recall which LNA you used?

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[Eduard Mol]

G8FEK L-band LNA. 

It is a good (but relatively pricey) unit, built by a ham radio guy in the UK

Op do 18 sep 2025 om 18:55 schreef Marcus D. Leech <patchv...@gmail.com>

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[Marcus D. Leech]

On 2025-09-18 13:14, Eduard Mol wrote:

G8FEK L-band LNA. 

It is a good (but relatively pricey) unit, built by a ham radio guy in the UK

Which SDR did you use?  Sorry for all the questions, just trying to figure out that "shape" of what an amateur capability here looks like.  I know that RTL-SDR
  devices are somewhat "iffy" above 1.5GHz.

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[Eduard Mol]

I used an Airspy mini for the observations with the 3 metre dish. The CAMRAS crew uses an Ettus USRP B210 if I recall correctly

Op do 18 sep 2025 om 19:20 schreef Marcus D. Leech <patchv...@gmail.com>

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[Marcus D. Leech]

On 2025-09-18 13:23, Eduard Mol wrote:

I used an Airspy mini for the observations with the 3 metre dish. The CAMRAS crew uses an Ettus USRP B210 if I recall correctly

OK, thanks.  The "mini" AirSpy has no external clock input, so the on-board clock is certainly adequate.  It would be interesting to do a bit of math
  on whether having a better reference clock improves detection SNR or not.  The maser lines are fairly narrow (less subject to Doppler spread) compared to
  H1, so it might be useful to extract a tiny bit more SNR out of the measurements...

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[Eduard Mol]

Hi Marcus, 

I did notice that the OH line of W3(OH) drifted by about 1.3 KHz (1 FFT bin) over the course of one of my observing sessions back in 2021. The OH maser line of this source is VERY narrow and easily fitted in one 1.3 KHz bin, so frequency drifting of the SDR can indeed be an issue.

Op do 18 sep 2025 om 19:27 schreef Marcus D. Leech <patchv...@gmail.com>

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[Marcus D. Leech]

On 2025-09-18 13:31, Eduard Mol wrote:

Hi Marcus, 

I did notice that the OH line of W3(OH) drifted by about 1.3 KHz (1 FFT bin) over the course of one of my observing sessions back in 2021. The OH maser line of this source is VERY narrow and easily fitted in one 1.3 KHz bin, so frequency drifting of the SDR can indeed be an issue.

Yeah, so the full-sized AirSpy R2 might provide a slight improvement in SNR, and GPSDOs are cheap these days...

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[Tyrone Bradford]

Have you looked at the Pluto+  Clone SDR. I have the RTL V3 and then recently purchased a pluto + clone and I've been very happy with it. The firmware install is a little bit more complex than RTL's airspy software install but not by much. I was able to get it running consistently with GNU radio. Which I love the radio chain workflow on GNU. 

[fasleitung3]

I had a look at our results of W3OH at high spectral resolution. The
attached plot is from January with 180 Hz resolution. I also checked
yesterday and got a similar result. Only the relative intensity of the
two main lines had changed a bit.
Given the with of the lines I would say that one does not neccessarily
have to be too concerned about frequency stability and resolution of
the recording. I have, however, not checked how much difference in
Doppler shift one would encounter during an observation over several
hours.
Best regards,
Wolfgang

> --

[fasleitung3]

It should read "January 2021"

[Marcus D. Leech]

On 2025-09-22 04:01, 'fasleitung3' via Society of Amateur Radio Astronomers wrote:

I had a look at our results of W3OH at high spectral resolution. The
attached plot is from January with 180 Hz resolution. I also checked
yesterday and got a similar result. Only the relative intensity of the
two main lines had changed a bit. 
Given the with of the lines I would say that one does not neccessarily
have to be too concerned about frequency stability and resolution of
the recording. I have, however, not checked how much difference in
Doppler shift one would encounter during an observation over several
hours.
Best regards,
Wolfgang

How much scintillation does this source experience? 

[fasleitung3]

I have no idea about the scintillation (if any). We have never done several observations on shorter timescales.

Wolfgang

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[Marcus D. Leech]

On 2025-09-22 11:41, 'fasleitung3' via Society of Amateur Radio Astronomers wrote:

I have no idea about the scintillation (if any). We have never done several observations on shorter timescales.

Wolfgang

Did a bit of research.  The OH1612 maser in V669 Cas is known to vary from about 110Jy to almost 300Jy.   That's not that severe, since both are
  reasonably detectable flux levels even on a modest instrument.

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[Eduard Mol]

Thanks Wolfgang!

Do you have any indication of the flux density? I understand it is hard to determine accurately but some “in the right ballpark” numbers would already be helpful for planning observation projects.

Best regards, 

Eduard

Op ma 22 sep 2025 om 10:01 schreef 'fasleitung3' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

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