I just looked at the Deep Space Network site DSN Now at https://eyes.nasa.gov/dsn/dsn.html and I saw that both dish numbers 25 and 26 are receiving a 8.42 GHz downlink signal from Voyager 1. Both dishes are 34 meters in diameter.

After watching for 20 more minutes, I can see that while both signal strengths drift by many dB, the CARRIER signal in number 25 always remains about 6dB weaker than the DATA signal in number 26.

Why does DSN sometimes uses two dishes at the same time to receive Voyager-1?

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above: screen shot montage from NASA's DSN Now page at about 02:52 UTC, July 23, 2016.

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    $\begingroup$ They'll do this for multiple spacecraft. I have definitely seen multiple dishes at one station targeting the same spacecraft many times. $\endgroup$ – Phiteros Jul 23 '16 at 3:20
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    $\begingroup$ Interesting photos at Goldstone DSN Complex Tour. I hadn't realized that sharks were such a problem so far inland. $\endgroup$ – uhoh Jul 23 '16 at 3:21
  • $\begingroup$ nice. I plan to make it out there some time this summer for a tour. $\endgroup$ – Phiteros Jul 23 '16 at 3:50
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    $\begingroup$ @Phiteros excellent - bring your shark repellant! fyi I've asked this question in stackoverflow. $\endgroup$ – uhoh Jul 23 '16 at 3:51
  • $\begingroup$ Oh! I read more carefully - it is a land shark - https://en.wikipedia.org/wiki/Land_Shark_(Saturday_Night_Live), and https://youtu.be/uDiNvEkBZ6E?t=96 and thus no surprise. $\endgroup$ – uhoh Jul 23 '16 at 4:05

If you look at the "more detail" section of the DSN status web page, you'll see that 25 and 26 are operating in "array mode". With two antennas receiving, twice as much incoming signal is being caught, and because the dishes are physically separated, some local noise sources will appear in one receiver and not the other, making it easier to discriminate signal from noise.

I note that both dishes are shown as receiving carrier, but only one is shown as receiving data. I suspect that this and the higher SNR figure is a presentation artifact, and both dishes are in reality receiving similar signal strength, but the combined signal strength is being shown for 26. That's just a guess, though, and I would expect a 3db improvement for a pair of antennas, not a 6db, so there may well be something else going on.

  • $\begingroup$ Aha! I didn't realize that there are two separate DOWN SIGNAL entries under each antenna. Each antenna is showing both CARRIER and DATA signals. Good catch - thanks! $\endgroup$ – uhoh Jul 23 '16 at 5:47
  • $\begingroup$ ...no I'm still not quite right about that either. I'll watch for another day or so. $\endgroup$ – uhoh Jul 23 '16 at 6:09
  • $\begingroup$ I just ran across this, in some cases when the weather is poor, the resulting SNR form one 34m may not be sufficient. youtu.be/FzRP1qdwPKw?t=342 $\endgroup$ – uhoh Apr 27 '17 at 20:42

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