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Ross 128 "The weird signal"
24th Jul, 2017 at 7:08pm
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There has been much interest recently in unusual signals observed by radio astronomers looking at star called Ross128.

Read their press release here: http://phl.upr.edu/press-releases/theweirdsignal



Ross128 was close to the geostationary line and their spectrum plot shows big signals below 4.2 GHz. Their abnormal signals were observed between about 4.58 and 4.8 GHz.

Have you seen anything like it due to a known cause or have any ideas ?

The signals are beyond the common 3.7-4.2 GHz C band range but it is normal for satellites to radiate some detectable weak signals outside their design range, particularly if under test with multiple full power CW and sweep test carriers.

Also, if you use a very large dish pointed at a high power satellite with carriers intended for small dish home users then you can get some strange effects when the LNB is overloaded.

Best regards, Eric.
  

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Re: Ross 128 "The weird signal"
Reply #1 - 5th Aug, 2017 at 9:34am
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Some ideas:

It is a broadband terrestrial signal and the amplitude and frequency variations are due to tropospheric scintillation and the antenna sidelobe patterns moving in the 0-5 deg elevation direction.

It is a broadband, steady, satellite signal and the amplitude and frequency variations are due to the sidelobe patterns moving.

It is intermodulation in the receiver due to a very high level carrier from 4, 12 or 27 GHz getting in via moving sidelobe.

More ideas welcome..
  

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Re: Ross 128 "The weird signal"
Reply #2 - 5th Aug, 2017 at 5:38pm
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Admin1 wrote on 5th Aug, 2017 at 9:34am:
Some ideas:

It is a broadband terrestrial signal and the amplitude and frequency variations are due to tropospheric scintillation and the antenna sidelobe patterns moving in the 0-5 deg elevation direction.

It is a broadband, steady, satellite signal and the amplitude and frequency variations are due to the sidelobe patterns moving.

It is intermodulation in the receiver due to a very high level carrier from 4, 12 or 27 GHz getting in via moving sidelobe.

More ideas welcome..

.
What is meant by sidelobes moving? That diffraction at low elevation varies a lot and quickly?
  
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Re: Ross 128 "The weird signal"
Reply #3 - 6th Aug, 2017 at 12:41pm
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The antenna was the Aricebo dish which is fixed reflector in a mountain depression and moving feed system suspended above.

The antenna will have a different far-out sidelobe pattern for every feed position and frequency.

When aimed at Ross 128 the main beam was moving at about 15 deg per hour so the sidelobe patterns were moving as well. I thought that a steady broadband signal, e.g. 30 MHz wide might peak up at different times according to frequency and thus produce the weird frequency sweeping effect with a bandwidth of 5-10 MHz.

The intermittent nature of the amplitude over the 10 minutes might be due to different sidelobes or tropospheric scintillation if the signals are of terrestrial origin.

It would be most helpful to have records of the 3.7-4.2 GHz range in similar waterfall view.

Does anyone have a 4 GHz dish and spectrum plotter, when NOT pointed directly at a satellite, and moving it 10 deg?.
« Last Edit: 6th Aug, 2017 at 3:14pm by Admin1 »  

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