Note: Since the link in the question actually gives a good answer I'll use it.
From Seth Shostak (SETI Institute), via Space.com:
The first episode of "I Love Lucy" was
broadcast sometime on October 15,
1951.
[The signal] is still going. Every day, that
first installment passes through an
additional 4 thousand trillion
trillion trillion cubic kilometers of
the cosmos.
Given that stars in our galactic
neighborhood are separated by about 4
light-years, it's easy to figure that
roughly 10 thousand star systems have
been exposed to "I Love Lucy" in the
past five decades.
That may suggest a
high Nielson rating, but the chance
that extraterrestrials are now hooked
on 1950s television is low.
[...]
Imagine that there are alien couch
potatoes 55 light-years away who,
bored with their own Fall lineup, have
constructed a LOFAR-style antenna (a telescope consisting
of 25 thousand tent-shaped antennas
spread across Holland and Germany) in
hopes of picking up "I Love Lucy's"
debut.
OK, how strong is that signal by the
time it reaches our putative alien
audience at 55 light-years distance?
Not very. The megawatt broadcast
washes over ET's world with a power
density of about
- 0.3 million million
million million millionths of a watt
per square meter,
which is not exactly
a scorching signal.
Could their LOFAR-style antenna find
that carrier, thereby indicating that
a program was on the air?
Well,
engineers have computed that at the
frequency of VHF television, LOFAR
will have an effective collecting area
similar to that of the 305-meter
diameter Arecibo antenna in Puerto
Rico.
That's big. That's brawny. But not
brawny enough. In our SETI experiments
at Arecibo, we could find a signal if
it were about 0.1 million million
million millionths of a watt per
square meter.
That number, you will
notice if you count up the words, is a
million times bigger than the "I Love
Lucy" carrier at 55 light-years. The
aliens' LOFAR would be inadequate to
detect the broadcast by a factor of a
million, a not entirely negligible
amount.
Simply stated: LOFAR couldn't
hear it.
LOFAR would only be able to find TV
signals comparable to ours from a
distance of much less than one
light-year!
From Radio Leakage: Is anybody listening?:
Hypothetically, assume that the
Arecibo telescope was put on the back
of a starship making its way into deep
space.
If it was possible to point the
telescope back towards Earth, how far
could the starship travel and still be
able to detect terrestrial
electromagnetic radiation leaking into
space?
Neglecting atmospheric effects:
- An AM radio broadcast could only be
detected out to 0.0074 Astronomical
Units (AU).
- FM Radio could be
detected out to 5.4 AU.
- A 5 Megawatt
UHF television picture could be
detected out to 2.5 AU, although the
carrier wave could be detected much
further; out to 0.3 light years.
(1 light year ~ 63,000 AU )
The SETI FAQ says:
Detection of broadband signals from
Earth such as AM radio,
FM radio, and television picture and sound would be
extremely difficult even at a fraction of a light-year
distant from the Sun.
For example, a TV picture having 5
MHz of bandwidth and 5 MWatts of power could not be detected
beyond the solar system even with a radio telescope with 100
times the sensitivity of the 305 meter diameter Arecibo
telescope.
From PopSci:
Frank Drake, the father of SETI,
worried that the switch from analog
television and radio signals to
digital cable and satellite radio
would render Earth invisible to aliens
looking for other life.
... as more and more people
receive their media beamed down to
them from digital satellites, not up
to them from analog radio towers, that
signal slowly fades away, drastically
reducing the chance that aliens might
detect our tiny blue rock.
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