Inverse Square Law: Explaining Reduced Data Rate w/ Distance

In summary: It would take longer to send a signal if you're farther away because it would be harder to get a clear signal.
  • #1
Drakkith
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Quoting from Wiki, bolded section mine:

Because of the inverse-square law in radio communications, the digital data rates used in the downlinks from the Voyagers has been continually decreasing the farther that they get from the Earth. For example, the data rate used from Jupiter was about 115,000 bits per second. That was halved at the distance of Saturn, and it has gone down continually since then. Some measures were taken on the ground along the way to reduce the effects of the inverse-square law. In between 1982 and 1985, the diameters of the three main parabolic dish antennas of the Deep Space Network was increased from 240 feet to 270 feet, dramatically increasing their areas for gathering weak microwave signals.

What exactly is going on here with the data rate? Is it just the strength of the signal that is falling off as distance increases? If so, how does that reduce the data rates that can be used? If not, what limits the data rates?
 
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  • #2
The farther away a source is, the weaker its signal, and the longer one needs to listen to determine whether a 1 or 0 is sent, so the slower the data rate has to be.
 
  • #3
Vanadium 50 said:
The farther away a source is, the weaker its signal, and the longer one needs to listen to determine whether a 1 or 0 is sent, so the slower the data rate has to be.

Can you elaborate on this?
 
  • #4
What part is unclear?
 
  • #5
Vanadium 50 said:
What part is unclear?

How listening longer helps you tell if it's a one or a zero. Something to do with how the carrier frequency is modulated?
 
  • #6
This is a statistical sampling effect. The further the signal is below the noise floor, the longer you must integrate to raise the signal or lower the noise. Integration time is a square law. To change the Signal to noise ratio by a factor of two takes four times longer. This is compounded by the range inverse square law.
 
Last edited:
  • #7
Ok, I see what you're getting at.
 

What is the Inverse Square Law?

The Inverse Square Law is a physical principle that states that the intensity of energy from a source decreases as the square of the distance from the source increases. This means that as the distance from the source increases, the energy is spread out over a larger area, resulting in a decrease in intensity.

How does the Inverse Square Law apply to data rates?

The Inverse Square Law also applies to data rates, as the strength of a signal decreases as the distance from the source increases. This means that as a device receives a signal from a source, the data rate will decrease as the distance between the two increases.

How does this affect data transmission in practical applications?

In practical applications, the Inverse Square Law can have a significant impact on data transmission. As data is transmitted over longer distances, the signal strength decreases, resulting in a decrease in the data rate. This can lead to slower data transfer speeds and potential errors in data transmission.

What can be done to counteract the effects of the Inverse Square Law?

To counteract the effects of the Inverse Square Law, various techniques can be used such as increasing the power of the signal, using repeaters or amplifiers to boost the signal strength, or using directional antennas to focus the signal in a specific direction.

Are there any limitations to the Inverse Square Law?

Yes, there are limitations to the Inverse Square Law. It is based on the assumption of a point source of energy, and in reality, sources may have different shapes and sizes which can affect the application of the law. Other factors such as interference, obstacles, and atmospheric conditions can also impact data transmission and may need to be taken into consideration.

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