Sadly laser beams suffer as much, if not more, from dispersion due to dust etc. as any other EM radiation. As others have said, to detect a laser beam in space you need to know where it is coming from, and where it is going... We may detect a laser by chance with one of the big optical telescopes, but it may well be discounted by the observer as "one of those things" unless it is sufficiently persistent to be observed for a long period of time, by several observatories.

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Bob Smith
Member of Seti PIPPS (Pluto is a Planet Protest Society)
Somewhere in the (un)known Universe?

I suspect that searching for ET signals from near a star may well be a waste of time.

Constructive/destructive radiation is only a factor if the frequencies are identical. Unless they are synchronized this basically never happens. We are talking about noise here. Maybe some of you remember the '70s vacuum cleaners that made your TV turn to snow every time they were turned on. Same idea.

Forget Voyager, how about the Mars rovers. I suspect that JPL takes a vacation two days a year when the Earth passes in front and behind the Sun. In any event communication would be impossible on those days. Predictable losses of signal are trivial things. Think of spacecraft passing behind the Moon.

I had to think about your vacuum example. As a former TV repairman, the distortion you see when turning on a vacuum cleaner is not affecting the signal itself, only the decoder (TV) The components in older TV's were susceptible to the RF generated by the vacuum motor, but the signal itself was unaffected. It today's worlds, that would be difficult to demonstrate, as the antenna did help (much of the RF came in through the cabinet) to transmit the RF from the vacuum into the electronics, but the channel decoder should have removed the signal, but it was also re-introduced with the rest of the electronics.

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

So you are saying the the RF noise from the vacuum affects the IF? The IF has already been amplified. I cant imagine that happening to cable TV, also an amplified signal.

Well obviously the laser would use a wavelength less susceptible to dust. IR and UV telescopes can see into Sagittarius-B which is completely blocked at optical wavelengths.

So you are saying the the RF noise from the vacuum affects the IF? The IF has already been amplified. I cant imagine that happening to cable TV, also an amplified signal.

Yes. The noise from the vacuum is much close to what is in the IF of the TV. If I remember correctly the interference existed on both VHF, and UHF. Those signals are way to high to be interfered with by what a vacuum puts out.

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

Obviously they made crappy TV's back then. Color TV's were really expensive too. I could not imagine designing one without a shielded IF. I believe my noise analogy is still valid though.

"Back then" the majority of small AC motors had pretty poorly designed brush gear, no effective suppression and so would broadcast quite effectively across everything from DC to light. At the same time IF strip design was "fairly immature", and so was susceptible to any nearby motor noise. It took a few years before TVs got effective IF strip cans, vacuum cleaners got half decent motors and the problem receded to where we are today.
The problem was less with cable, but was still there - there was still an IF strip, albeit running at a lower injection frequency that "from the air" transmissions. (I do remember modifying my grandparents cable only TV to pick up from the air stuff, it was a fairly simple change of an inductor and a few other passives to give them a really wide band IF.....)

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Bob Smith
Member of Seti PIPPS (Pluto is a Planet Protest Society)
Somewhere in the (un)known Universe?

Why would you want a wide IF? From ham radio I know that you want the narrowest IF possible for the application. IE for CW you want a 500HZ IF. You used to have to pay extra for those filters.