Eric's Weekly Post #3 (Warning, science enclosed. Do not fold or bend.)


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Message boards : SETI@home Staff Blog : Eric's Weekly Post #3 (Warning, science enclosed. Do not fold or bend.)

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Profile ML1
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Message 547377 - Posted: 16 Apr 2007, 22:55:15 UTC - in response to Message 547325.

AN/FPS-117

air traffic control and air search.

Well, we already know where Arecibo is. We don't need to re-find it!... And we certainly don't want any UFOs to be positively identified either!!


Hopefully, discussions are in progress before the HARMs go in?...

Cheers,
Martin

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Message 547668 - Posted: 17 Apr 2007, 8:40:23 UTC - in response to Message 520727.

Is there a weather radar near by? Perhaps your picking up sidelobes or back lobes getting into the sidelobes of the receiving antenna? Sidelobe poke through or sibelobe of a separate transmitter getting into the sidelobe of the receiver? I am not actually suggesting radar, but even perhaps unshielded equipment nearby?

Many years ago very quiet night I could pick up the airport radar at Lindberg Field (or possibly the North Island Naval Station) on my CB radio. Gotta watch out for those harmonics.


That was more likely direct front end overload. I used to get the sweep right next to I-5 just north of the main gate to Camp Pandleton when I lived in base housing as a teen on my boom box tape deck (via the audio amplifier, not the radio), radio, clock radio, and shortwave radio. It would be audible on each sweep.

I might add that the FCC and NTIA maintain radio blackout zones around radio telescopes (for instance see the restrictions under 47 CFR Part 97 Sec. 303(k))

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Message 547673 - Posted: 17 Apr 2007, 8:51:14 UTC - in response to Message 522273.

[quoteThe two liniear polarisations of each ALFA beam can be combined to give both circular ("helical") polarisations. SO we could do the s@h search on FOUR polarisations per beam to give 4 x 7 = 28 streams of data.

I wonder if a bit more programming for the data splitting could add searching the circular polarisations?
[/quote]

I would think that if we are looking for ET at these frequencies, that ET has the same issues with beaming a linear polarization from the surface of it's planet as we do from ours.

Because of Faraday Rotation, most space communications between Earth and something in space are circularly polarized, because circular polarization makes the effects of faraday rotation negligible.

I would assume that ET's planet has a magnetic field too that causes similar effects.

It's said that one of the very first Earth-Moon-Earth contacts was from Arecibo using the 430 MHz disc feed that no longer exists (the one the bad guy in that Bond movie gets skewered with).

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Message 548658 - Posted: 18 Apr 2007, 18:51:57 UTC - in response to Message 547276.


The pulses show up at band center frequencies regardless of the local oscillator settings because the pulses are strong enough to saturate the mixers. That's primarily fooled us into thinking it was an instrumentation problem. (The local oscillator is how the observing frequency band is tuned within the receiver band.)

The Punta Salinas website table gives the duration of the pulses, 41.2 and 409.6 microseconds. I didnt check the frequencies of of the occurrences of the pulses; they might be there, too. The frequencies of the signals themselves are just below those of Seti, from about 1.2 to 1.4 GHz.


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