Voyager I S/N ratio

danadak

Well-Known Member
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From ChatGPT -

The signal-to-noise ratio (SNR) of Voyager 1's signals as received on Earth is influenced by several factors, including the vast distance between Earth and Voyager 1, as well as the sensitivity of the receiving equipment.


As of now, Voyager 1 is over 14.5 billion kilometers (or about 9 billion miles) from Earth, which is roughly 124 AU (astronomical units). The signal strength decreases with the square of the distance, meaning that as Voyager 1 moves farther away, the strength of its signal diminishes significantly. This results in a lower SNR because the background noise (e.g., thermal noise, cosmic radiation, and interference from Earth’s atmosphere and the receiving system) remains relatively constant.


At this distance, the Voyager 1 signal is incredibly faint by the time it reaches Earth. To detect it, the receiving stations, such as those at NASA's Deep Space Network (DSN), use highly sensitive equipment, including large parabolic antennas with diameters up to 70 meters (about 230 feet). Even so, the signal is very weak compared to the background noise.


To give you a rough estimate:


  • The signal strength received from Voyager 1 is around -150 dBm (decibels milliwatts), which is extremely faint.
  • The noise floor at the DSN’s most sensitive receivers is typically around -140 dBm.
  • This results in an SNR of approximately 10-20 dB, which is considered quite low but still detectable due to the highly specialized equipment and techniques employed.

While the exact SNR fluctuates with factors like interference, space weather, and any adjustments to the receiving systems, this gives a rough ballpark of the situation today. The signal is processed using advanced digital signal processing techniques to extract the data, making it possible to maintain communication with Voyager 1 despite the vast distance.
 
Has ChatGPT got that right? The signal level quoted is less than the noise level, so isn't the SNR minus 10dB ?
 
A signal below the noise floor can be recovered if it is repetitive, by summing multiple sequential receiver signal patterns.

The noise tends to cancel out while the wanted signal adds and gradually becomes clearer.

A simple analog version of this has been used by some DXTV (analog long distance TV reception) enthusiasts, to identify signals below noise - take a very long exposure photo of a display while a testcard or station logo are known to be broadcast & the result can be quite clear.
 
The free-space path loss over this distance is roughly 317 dB. The Rx baud-rate may be reduced to 40 Hz or less.
 
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