Didn’t realize the math would be that straightforward. Is there something the author isn’t taking into account or is that a decent plausible range?
I was surprised, too. Knowing little about physics, this was a pleasant surprise, however.
How many photons are received per bit transmitted from Voyager 1?
11–20 of 205 posts
Re: How many photons are received per bit transmitted from Voyager 1?
#12I love these kinds of questions. So what does that conclusion mean about when the probe will be so far away that we are below the Shannon limit? And can we beat the Shannon limit somehow, eg collect for longer, put the dish outside the atmosphere, and so on?
The Shannon Limit is fundamental so you can't get around it directly. But yes, there are things you can do to receive information from further away.
1) A bigger dish is the most obvious one.
2) Use a lower bitrate to send more energy per bit at the same transmitter power.
3) Reduce the effective receiver temperature. This is a case where putting it outside the atmosphere might help in reducing noise.
Re: How many photons are received per bit transmitted from Voyager 1?
#13TLDR; 4e22 photons per second 2.6e22 per bit.
For comparison, ~2e26 photons will be received through your iris in your life
Re: How many photons are received per bit transmitted from Voyager 1?
#14I am confused. I thought photons were just visible light but I guess these little buggers are everywhere. Also very surprised voyager is using 2.3ghz, that's crazy saturated on earth due to wifi. How these engineers make this all work, is magic to me.
Re: How many photons are received per bit transmitted from Voyager 1?
#15Didn’t realize the math would be that straightforward. Is there something the author isn’t taking into account or is that a decent plausible range?
It looks like a pretty reasonable order of magnitude estimate to me. Energy arguments tend to be quite neat for that because if the efficiency is at all reasonable they constrain things well with fairly simple calculations. The antenna directionality is also reasonably well understood and characterised. The exact noise level discussed later on is probably where things get a bit more uncertain (but aren't directly needed to answer the question).
Re: How many photons are received per bit transmitted from Voyager 1?
#16TLDR; 4e22 photons per second 2.6e22 per bit. For comparison, ~2e26 photons will be received through your iris in your life
Does this number account for all photons or just those in the rather narrow optical band?
Then again RF photons just don't fit through the pupils and will get backscattered, i guess.
Re: How many photons are received per bit transmitted from Voyager 1?
#17TLDR; 4e22 photons per second 2.6e22 per bit. For comparison, ~2e26 photons will be received through your iris in your life
How many of them come from Voyager 1?
Re: How many photons are received per bit transmitted from Voyager 1?
#18I love these kinds of questions. So what does that conclusion mean about when the probe will be so far away that we are below the Shannon limit? And can we beat the Shannon limit somehow, eg collect for longer, put the dish outside the atmosphere, and so on?
Seems like we can just build a bigger receiving dish
There's not a lot of appetite for that, though. the 70m receiver is already one of the largest ever built, and for most use cases it's looking better to use an array of smaller ones. Which works fine for receiving but not so much for transmitting (while there are multiple sites in the world capable of receiving from voyager 2, there's only one dish which can actually transmit to it)
(I recall seeing a video on that dish, and the director seemed confident there was enough noise margin left that voyager's power would fail before they lost contact with it)
Re: How many photons are received per bit transmitted from Voyager 1?
#19I am confused. I thought photons were just visible light but I guess these little buggers are everywhere. Also very surprised voyager is using 2.3ghz, that's crazy saturated on earth due to wifi. How these engineers make this all work, is magic to me.
Electromagnetic radiation includes visible light, radio spectrum, X-rays, etc. Photons.
Re: How many photons are received per bit transmitted from Voyager 1?
#20I am confused. I thought photons were just visible light but I guess these little buggers are everywhere. Also very surprised voyager is using 2.3ghz, that's crazy saturated on earth due to wifi. How these engineers make this all work, is magic to me.
> Also very surprised voyager is using 2.3ghz, that's crazy saturated on earth due to wifi
Wifi didn't exist when Voyager was launched...