This is so cool and would have made such an impact on me as a kid if I got to see it in action. I wish we could better demonstrate this sort of thing in middle school or high school science classes, such as how easy it is to download a weather satellite image live, via SDR.
He doesn't sound like an amateur at all
I don't know if it's a British joke, but recall that "amateur" in "amateur radio" means "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest " (International Radiotelegraph Convention of Washington, 1927), i.e. anyone working with radio for the hobby, not for the job salary.
The Camras team is maintaining and operating the telescope on their own time. The members have dayjobs like programmers and scientists, or are retired professionals. So I'll go with the first definition.
Communication with satellites in the US requires the highest level of amateur licensing called the Extra.
I'm now imagining the on-line radio amateur community poking fun at themselves when the recent slang interpretation of "extra" came along.
If the aviation world used similar terms a private pilot would be called an amateur pilot.
It means ham as in ham fisted, as in amateurish or unskilled.
See the Wikipedia entry for more info https://en.wikipedia.org/wiki/Amateur_radio
"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.
Amateur is short for "Amateur Radio operator", eg someone who holds an Amateur Radio License.
http://lilacsat.hit.edu.cn/DSLWP-B/865fbeb5-116d-4f6a-bb86-0...
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.
Depends. In the US where media companies write copyright law and hand it to legislators, yes. In China where there appears to be no Rule of Law, no.
With your background you'd probably need to devote time mostly to learning the rules and regulations. You can take all 3 tests in one sitting for a $15 fee and be done with it. Each test gets you more privileges (power, frequencies).
Even without a license you can receive with a cheap SDR and home brew antenna. This blog has many examples of that: https://www.rtl-sdr.com/
Finally, you may want to find a local club. Usually visiting during a "contest" will enable you to get on the air. In the US you don't need a license to use the radio if you are with a properly licensed operator.
Hope you find the hobby as fun as I have.
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/
I expect the data to be transferred one pixel at a time, but possibly, it’s losslessly compressed.
It’s “Dutch radio amateurs image” because they controlled the camera.
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
The radio link is effectively just a modem (short for 'modulate/demodulate') that transforms bits into some modulation of a radio signal. A simple and error-prone modulation would be to just shift the frequency back and forth between two values such that the lower frequency represents a binary zero and the higher a binary one. The receiver listens to the RF coming from the transmitter, and if it applies the same algorithm to demodulate the signal back to bits, will start kicking out bits that turn to bytes that turn to pixels or telemetry or navigational data or whatever the satellite wishes to send. So in this case, it could be something approximating a standard digital camera, computer snaps a photo, maybe stores it on a filesystem, queues it up to send and when the time is right starts blasting bits down the RF pipe back to earth.
In my very limited experience with this the satellite will typically send a simple raw lossless bitmap or similar encoding to minimize the effect of data loss for individual pixels.
I did find a short blurb on the Longjiang-2 modulation types:
"While receiving signals from satellites in low Earth orbit requires only relatively simple antennas, doing so for satellites in orbit around the Moon (a thousand times more distant), is much harder. To this end Longjiang-1 and 2 transmit signals in two low data-rate, error-resistant, modes; one using digital modulation (GMSK) at 250 bits per second, while the other mode (JT4G) switches between four closely spaced frequencies to send 4.375 symbols per second. This latter mode was developed by Nobel-prize winning astrophysicist Joe Taylor and is designed for radio amateurs to relay messages at very low signal strengths, typically when bouncing them off the surface of the Moon."
GMSK stands for Gaussian minimum shift keying [1] and is also used for GSM mobile phone data transmission. It's a fairly sophisticated frequency shift keying that minimizes phase disturbance between the shifted frequencies.
JT4G is a simple frequency shift keying modulation. Here's [2] a recording of it from Longjiang-2, turn up the volume to hear the downconverted audio.
[1] https://en.wikipedia.org/wiki/Minimum-shift_keying#Gaussian_...
