Grupa: Administrator 
Lokalizacja:: Kłodzko JO80IK06AO
Posty: 41754 #7253908
Od: 2013-10-18
Ilość edycji wpisu: 3 | HAM RADIO SIGNALS FROM MARS: Ham radio operators are doing something that until recently only big Deep Space Networks could do. "We're monitoring spacecraft around Mars," says Scott Tilley of Roberts Creek, British Columbia, who listened to China's Tianwen-1 probe go into orbit on Feb. 10th. The signal, which Tilley picked up in his own backyard, was "loud and audible." Click to listen:
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The signal Tilley received from Tianwen-1 is dominated by a strong X-band carrier wave with weaker side bands containing the spacecraft's state vector (position and velocity). Finding this narrow spike of information among all the possible frequencies of deep space communication was no easy task.
"It was a treasure hunt," Tilley says. "Normally a mission like this would have its frequency published by the ITU (International Telecommunications Union). China did make a posting, but it was too vague for precise tuning. After Tianwen-1 was launched, observers scanned through 50MHz of spectrum and found the signal. Amateurs have tracked the mission ever since with great accuracy thanks to the decoded state vector from the probe itself."
So far, Tilley has picked up signals from China's Tianwen-1 spacecraft, NASA's Mars Reconnaissance Orbiter, and the United Arab Emirates' Hope probe--all orbiting Mars approximately 200 million kilometers away. How is such extreme DX'ing possible?
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"It helps to have a big antenna," says Tilley, who uses a 60 cm dish, pictured above. "But the real key," he says, "is the advent of Software Defined Radios (SDRs), which have become the norm for hams in the past decade or so."
In a Software Defined Radio, computers digitally perform the signal mixing and amplification functions of circuits that used to be analog, software has replaced hardware. SDRs are cheap, sensitive, and they give hams the kind of exquisite control over frequency required to tune into distant spacecraft.
"Amateurs began listening to deep space probes in the late 1990s and early 2000s," says Tilley. "This sparked an awareness that it was possible. The combination of improving technology and growing awareness has resulted in more and more interplanetary detections."
Next up: NASA's Mars 2020 spacecraft carrying the Perseverance rover, due to land in Jezero crater on Feb. 18th:
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Tilley plans to listen but he doesn't expect a strong signal. "Perseverance does not have a very large antenna," says Tilley. "It doesn't need one because it can relay data through other NASA spacecraft in Mars orbit. The signal will therefore be weak and I doubt many amateurs will record the landing."
Tianwen-1, on the other hand, has a relatively large antenna with a booming signal. "China probably plans to use it as a relay for future Chinese Mars missions," Tilley speculates. "This makes it a good target for hams hoping to bag their first Martian spacecraft."
Update: Joe at USA Satcom (Twitter handle @usa_satcom) has picked up a weak signal from Mars 2020. So it is possible.
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