[biblewonk]

Thus, our ability to detect weak signals improves much faster than our ability to resolve weak signals, as the size of our instruments increase.

I'm an ATM so I know the difference between resolution and light gathering ability thanks.

So do the math and figure out what the requirements for LGM to send a signal that we could detect give that 8 watts is detectable from a 10ish foot dish from 5 billion miles away by a 300 foot dish. Detectable in the sense that we can actually decode data, though at a low data rate. We need more than just a carrier since every single object out there is transmitting a carrier. We need intelligence modulated onto it.

[longshadow]

So do the math and figure out what the requirements for LGM to send a signal that we could detect give that 8 watts is detectable from a 10ish foot dish from 5 billion miles away by a 300 foot dish. Detectable in the sense that we can actually decode data, though at a low data rate. We need more than just a carrier since every single object out there is transmitting a carrier. We need intelligence modulated onto it.

I'm going to defer this one to "RadioAstronomer" since it is right up his alley. He will know what the limit on detector sensitivity is, etc. much better than I do.

I think he will disagree with your premise about having to to detect more than a carrier.

[Physicist]

What's an ATM? I assume you don't dispense cash or switch packets. ;-)

The goal of SETI is not to decode the signals, it's just to see whether they are there.

There simply aren't any natural narrowband radio sources in the relevant channels. In the bands that we use for communications, Earth is at least 1000 times brighter than any natural source in the galaxy. You can't hear the sun with a transistor radio, even though it subtends an area far larger with respect to your radio than any antenna you're likely to listen to.

[RadioAstronomer]

So do the math and figure out what the requirements for LGM to send a signal that we could detect give that 8 watts is detectable from a 10ish foot dish from 5 billion miles away by a 300 foot dish. Detectable in the sense that we can actually decode data, though at a low data rate. We need more than just a carrier since every single object out there is transmitting a carrier. We need intelligence modulated onto it.

Two things: 1. The s/n ratio goes through the roof as we shrink our detection into narrower and narrower bands. 2. We are looking a millions and sometimes billions of frequencies simultaneously.