Dang...and I thought we would find all the aliens on the dark side of the moon. Where did they all go?
Dutch radio amateurs image far side of the Moon using Chinese satellite data
51–60 of 62 posts
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#52How do pixels work in radio astronomy? Does the antenna only capture one pixel every time the "shutter" is opened and then move to the next position?
It depends on the type of observations being made. If it is done with a single dish with a single antenna feed then to make images you just have to know when and where you are pointing while you record the power.
But most images you see of radio astronomy are done with interferometers. This means you use multiple pairs of antenna. Each pair will respond to a point source going across the sky with the interference pattern modulating the voltage at the receiver that follows an acos pattern relative to the distance between the antennas in the pair.
The multiple pairs of antenna all each contribute a 2D fringe pattern. The interference makes the receivers record what is essentially the fourier transform of the sky. So some pair might have sine wave of a particular wavelength and angle, and another pair another angle. By combining all these 2D patterns of waves the sum ends up being an "image" of the sky (convolved with the primary and sidelobe beams).
That gets you a "DIRTY" image, and it really is dirty. The beam of an interferometer is a complex thing. So after that multiple types of cleaning algorithms may be used to use prior knowledge to pull just the actual signal out of the noisy, gunked up "image".
So in the end each pixel is really the result of a somewhat arbitrary algorithm picking out the bright bits after taking the FFT of the sky of each baseline pair and combining them.
If you want to know more I recommend running the python (cross platform) interferometry simulator https://launchpad.net/apsynsim while watching the video lecture series at https://www.youtube.com/watch?v=0TwnZhiEc3A and then https://www.youtube.com/watch?v=mRUZ9eckHZg
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#53Rock on, amateur operators!
HAMs did the same thing in the 60s, decoding Soviet communications coming from the moon, which were the first closeup images of the surface at the time. They released the images to wide fanfare, and did a lot to defuse the Soviets' political agenda of holding this accomplishment above the western world.
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#54> designed by radio amateur and Nobel prize winning astrophysicist Joe Taylor He doesn't sound like an amateur at all
The word amateur has two different meanings in English. "1. a person who engages in a pursuit, especially a sport, on an unpaid rather than a professional basis" "2. a person who is incompetent or inept at a particular activity" Here we refer to the first definition. The English word amateur comes from French "lover of". Someone who does things just because they like it, not because they get paid to do it.
It should be obvious that there is a third meaning..
Amateur is short for "Amateur Radio operator", eg someone who holds an Amateur Radio License.
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#55So interesting! How do you send "error-resistant digitally modulated transmissions"? Is that the same thing as a duplex signal? Is there other technology used nowadays?
It's probably error corrected code. Some examples are CRC, ECC menory, and Raid-5 disk array.
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#56This is amazing! I have a background in physics and electronics, but I have never been involved in amateur radio. However, I would love to and would like to ask if one could point me to resources for delving into it? When it comes to math and e.g. electrodynamics and practical filters, I wouldn't need an introduction. Thanks!
There is lots of cool science to be done with radio, being done by amateurs. Starting with the Society for Radio Astronomy mentioned already, but also see:
http://www.radio-astronomy.org/
SARA members have a lot of projects going on, from beginner stuff to full blown SDRs http://www.radio-astronomy.org/projects
Radio Astronomy Software Defined Radio (RASDR): http://www.radio-astronomy.org/rasdr
SuperSID: Sudden Ionospheric Disturbance monitor: http://www.radio-astronomy.org/node/210
Radio Jove: Radio emissions from Jupiter: https://radiojove.gsfc.nasa.gov/
Personal Space Weather Station: http://www.hamsci.org/basic-project/personal-space-weather-s...
Reverse Beacon Network: http://www.reversebeacon.net/
Weak Signal Propagation Reporter Network: http://wsprnet.org/drupal/
PSK Automatic Propagation Reporter: https://pskreporter.info/
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#57So interesting! How do you send "error-resistant digitally modulated transmissions"? Is that the same thing as a duplex signal? Is there other technology used nowadays?
Could be coding (Turbo coding is where it's at, while hamming (no relation) error correcting codes are purely digital and ubiquitous), could be simple double transmissions separated in the time domain as in FEC SITOR/AMTOR. My money's on Turbo coding. https://en.wikipedia.org/wiki/Turbo_code
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#58Dang...and I thought we would find all the aliens on the dark side of the moon. Where did they all go?
They are deep in Uranus.
Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#59Earlier quoted context omitted.
unpaid as in never having done something as a paid profession. A professional software developer who retires and programs as a hobby is not suddenly an amateur developer.
I don't think there's a definition like that anywhere. Only if you define 'amateur' as some who doesn't really know the trade. We should remember that 'amateur' actually means "lover of", i.e. that an amateur is simply someone doing it because they love to (as opposed to "just" because they're paid to do it). It doesn't say anything about the level.
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Re: Dutch radio amateurs image far side of the Moon using Chinese satellite data
#60How do pixels work in radio astronomy? Does the antenna only capture one pixel every time the "shutter" is opened and then move to the next position?
The same way pixels for on your phone camera. The only difference is the file/data is transmitted over a different transport.
Oh I thought it was imaging in the radio spectrum but actually it's not.