Is Voyager I’s reduced data transmission rate as described in this article because of the distance or because its transmitter getting older & slower?

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    $\begingroup$ This is off topic on Astronomy, though it may be on topic on Space Exploration However the answer to the question is in the article "Due to the 14-billion-mile distance, the communication rate has since slowed to 160-bits-per-second, or about half a 300-baud rate." The slowness is due to the distance which makes the signal weak $\endgroup$
    – James K
    May 11, 2021 at 5:46
  • $\begingroup$ Welcome to astronomy SE! Don't be dishearted about the close-votes, I am sure the audience at Space Exploration will be happy to answer. $\endgroup$
    – B--rian
    May 11, 2021 at 6:42
  • $\begingroup$ My question was inspired by curiosity whether the slowing comm rate was due to added noise or increasing redshift of comm signal. (sorry I didn't think of expressing my question this way originally)... if redshift does contribute to slower data transmission rates, I would think that's at least somewhat "astronomy" related... oh well, thanks for your comments & I do appreciate your adherence to keeping to the subject. $\endgroup$ May 12, 2021 at 16:58
  • $\begingroup$ @JamesK would it be ok if I reworded (or resubmitted) this question as something like "Is Voyager I’s reduced data transmission rate as described in article below because of noise/interference, or increased redshift of signal, or because its transmitter getting slower?" because if the answer is at least partially due to red-shift, than this is an "Astronomy" question (not Space Exploration) I would think? I'm mostly curious about the role red-shift plays. Thanks. $\endgroup$ May 12, 2021 at 18:52
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    $\begingroup$ As it is about space operations, the question would be best on Space Exploration If there is an astronomical reason (like redshift) then the space experts would still know about it. I think you have a major misconception about "redshift" and perhaps "how big the universe is". Hubble redshift doesn't occur until you are well beyond the galaxy. and Voyager has barely left the solar system. $\endgroup$
    – James K
    May 12, 2021 at 19:04

1 Answer 1


Transmitters don't slow down as they age. Red shift isn't involved, at all. As a transmitter gets further away the signal at the receiver gets weaker, so it's deliberately slowed down. Data channel capacity depends on signal to noise ratio and bandwidth. As the signal gets weaker the data rate can be slowed to reduce the necessary bandwidth. Noise doesn't increase: it's just a loss of signal strength at the receiver. Narrowing the receiver bandwidth reduces the noise received, but also limits the information bandwidth.

  • $\begingroup$ This is a little subtle, but when they reduce the data rate it's not exactly always a reduction in bandwidth because of the complicated modulation scheme they use. There may have been some drops in bandwidth, but when the data rate drops sometimes it may be more like including more repeats of a smaller block of data in a given time period. See section 2.2.4 Telemetry Modulation in Article 4; Voyager Telecommunications for example. $\endgroup$
    – uhoh
    May 14, 2021 at 1:41
  • $\begingroup$ @uhoh repeating of a smaller block of data is a reduction of information bandwidth. $\endgroup$
    – stretch
    May 15, 2021 at 13:50
  • $\begingroup$ In the context of signals processing and radio communications the bandwidth $\Delta f$ is a range of frequencies, measured in Hz. The maximum theoretical channel capacity $C$ in bits per second via Shannon-Hartley is then $$C = \Delta f \ log_2 \left(1 + \frac{S}{N}\right)$$ where $S$ and $N$ are the signal and noise powers within the fully-used bandwidth $\Delta f$. $\endgroup$
    – uhoh
    May 15, 2021 at 20:34
  • $\begingroup$ bandwidth (computing) or information bandwidth is a term that applies in wide swaths of digital communications on Earth, in supercomputer interconnect schemes, in internet connections, etc. But when we're talking about trying to hear Voyager's faint signals with giant dishes, bandwidth is the range in frequencies (Hz) data rate in bits per second is some fraction of the channel capacity (bits per second). $\endgroup$
    – uhoh
    May 15, 2021 at 20:37

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