Graph "Data Gap"

Message boards : SETI@home Science : Graph "Data Gap"
Message board moderation

To post messages, you must log in.

AuthorMessage
Timothy Catron

Send message
Joined: 4 Oct 14
Posts: 4
Credit: 402,650
RAC: 0
United States
Message 1587573 - Posted: 16 Oct 2014, 2:33:36 UTC

When I am not programming, I occasionally look at the seti graphs which the boinc client provides. After searching through several of them, this graph caught my eye.


As you can see, at a specific frequency, there is a small gap in the data/graph. Is this most likely a bug in the program or radio interference? The task finished rather quickly (50 seconds).

What do you guys think could have caused this abnormality?
Here is a link to the specific task: http://setiathome.berkeley.edu/result.php?resultid=3785848770
It came up with 30 spikes, so my guess would be radio interference.

Also, since this is my first post here, please move this post to the correct section if it is not already there.
ID: 1587573 · Report as offensive
Profile Bob DeWoody
Avatar

Send message
Joined: 9 May 10
Posts: 2848
Credit: 1,215,556
RAC: 143
United States
Message 1587582 - Posted: 16 Oct 2014, 3:18:20 UTC

I've seen it happen before. Most likely, I would guess, a loss of signal in that frequency band.
Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.
ID: 1587582 · Report as offensive
Timothy Catron

Send message
Joined: 4 Oct 14
Posts: 4
Credit: 402,650
RAC: 0
United States
Message 1587752 - Posted: 16 Oct 2014, 10:44:54 UTC

I was brainstorming earlier. Could something like a hydrogen cloud (nebula for example) absorb only a small spectrum of a radio signal if one exists between the source and earth?
ID: 1587752 · Report as offensive
Michael Watson

Send message
Joined: 7 Feb 08
Posts: 939
Credit: 1,115,188
RAC: 1,434
Message 1587832 - Posted: 16 Oct 2014, 15:59:11 UTC

I've read that certain frequencies are purposely excluded because they routinely receive interference from nearby transmitters. Puerto Rican radars have been mentioned, in this regard.
ID: 1587832 · Report as offensive
anniet
Volunteer tester

Send message
Joined: 2 Feb 14
Posts: 6749
Credit: 1,087,504
RAC: 504
Message 1587880 - Posted: 16 Oct 2014, 17:25:11 UTC

Hi Timothy :) Can't contribute anything to the topic - but lovely to find a new member on the boards. :) Welcome to seti - it's nice here :)
ID: 1587880 · Report as offensive
Timothy Catron

Send message
Joined: 4 Oct 14
Posts: 4
Credit: 402,650
RAC: 0
United States
Message 1588021 - Posted: 16 Oct 2014, 23:06:13 UTC - in response to Message 1587832.  
Last modified: 16 Oct 2014, 23:11:34 UTC

Interesting. Is there a paper which documents the various types of radio interference or abnormalities in the data? As a student, I am always curious. Also, Anniet, thanks for the welcome.
ID: 1588021 · Report as offensive
Profile ML1
Volunteer tester

Send message
Joined: 25 Nov 01
Posts: 9370
Credit: 7,045,815
RAC: 4,753
United Kingdom
Message 1588043 - Posted: 17 Oct 2014, 0:08:23 UTC

Note the frequency of exactly 1.42GHz...

The frequency spectrum trough at that point is a well know artifact of the data collection. There are lots of prior posts about it and it is in the FAQ.

Sorry, nothing but an artificial artifact of how we collect and process the data.


Good find but keep searchin'!

Cheers
Martin
See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)
ID: 1588043 · Report as offensive
Josef W. Segur
Volunteer developer
Volunteer tester

Send message
Joined: 30 Oct 99
Posts: 4504
Credit: 1,414,761
RAC: 0
United States
Message 1588044 - Posted: 17 Oct 2014, 0:13:51 UTC

Pulsed Radar signals definitely wouldn't cause the kind of pattern you saw with a narrow band of frequencies suppressed for the full 107.374 second duration of the WU. In any case, the actual radar frequencies are lower than those we're searching, but powerful enough to overload the receiver front end and affect our data (and that's the radar signal as reflected from airplanes).

That narrow range reduction around 14 or 15 KHz. above the central 1.42 GHz. of the recorded band could have been deliberately inserted as a test, or it could be a flaw in the pfb_splitter code, or any of many other things. It definitely looks to be a constant frequency, so likely of terrestrial origin if it represents some RFI source.
                                                                   Joe
ID: 1588044 · Report as offensive
Timothy Catron

Send message
Joined: 4 Oct 14
Posts: 4
Credit: 402,650
RAC: 0
United States
Message 1589463 - Posted: 20 Oct 2014, 22:10:10 UTC - in response to Message 1588044.  

After some insightful answers, I read up about various radio frequencies on a few scholarly articles, and types of possible interference with SETI. I still have one question. Does this mean that (almost) every signal detected which is around 1420mghz with a Doppler shift of near zero is terrestrial? For instance, this is likely narrowband interference...

I read that a likely alien signal would probably not even be noticeable on the graph unless it went through computer analysis. It might look like a regular series of spikes or pulses in our data. Correct? Thanks for any answers in advance. [From a high school student]
ID: 1589463 · Report as offensive

Message boards : SETI@home Science : Graph "Data Gap"


 
©2017 University of California
 
SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.