bolddcex

Then, what do we have:

Rmax = 1.04E9 * Dr meters

So Rmax = 1.10E-7 * Dr light-years

So it would take a receiving dish of diameter 9,100 km to receive our TV broadcasts out to a distance of 1 light-year. To receive our full TV video and audio signal out to a distance of 1,000 light-years the receiving dish must have a diameter of 9.1 million km. This seems outlandish to us but it may very well be within the capabilities of an advanced extraterrestrial civilization.

If we consider only the audio portion of the signal then the bandwidth improves from 6.0 MHz to 10 kHz and the diameter of the dish needed to receive just the audio portion out to a distance of 1,000 light-years is 370,000 km.

Add a little directionality to the signal, say let the transmitting dish (upload to satellite) have a diameter of 10 meters with wavelength of 64 cm, then the diameter of the receiver needed shrinks to 7,500 km to pick up our TV audio out to 1,000 light-years, 750 km to pick up our TV audio out to 100 light-years, and 75 km to pick up our TV audio out to 10 light-years. Some of these receiver sizes might even be feasible for our civilization in the distant future. So yes, it is possible for an advanced ET to pick up our TV signals at great distances.

Not with the atmosphere getting in the way. RV precision is almost at the level of atmospheric distortion (if it’s not already there). The sooner we get Obama in office, the sooner we’ll be able to get the space missions going again, which, incidentally, have been put on hold because of all the money and resources being funneled away to satisfy Bush’s fetish of getting man on Mars.

This is a common misconception that our TV signals fade out to zero past some certain point. The distance at which the signal falls below background noise depends on the collecting area of the receiver.

The equation for a directional transmitter is:

factor1 = Tb + Tn / SQRT(tau-r * Br)

factor2 = k * Bt * SNR * factor1

factor3 = Pt / factor2

factor4 = pi * Dt * Dr / (4*lambda)

Rmax = factor4 * SQRT(factor3)

For an isotropic transmitter the equation is:

Rmax = (Dr / 4) * SQRT(factor3)

Tb = background noise temperature of sky (deg K)
Tn = noise temperature of receiver (deg K)
tau-r = integration time of receiver (sec)
Br = bandwidth of receiver (hertz)
k = Boltzmann’s constant = 1.381E-23 joule per deg K
Bt = bandwidth of transmitter (hertz)
SNR = signal to noise ratio (typically greater than 1)
Pt = transmitter power (watts)
pi = 3.14159…
Dt = diameter of transmitting parabolic dish (meters)
Dr = diameter of receiving parabolic dish (meters)
lambda = wavelength of the signal (meters)
Rmax = maximum distance over which trasmissions are detectable by the receiver (meters)

Let’s consider television signals. Let’s assume the transmission is UHF channel 14 which has a video carrier at 471.25 MHz. The brightness temperature of the sky at this frequency is quite high, about 30 deg K. If it’s an NTSC signal (United States standard) then Bt is about 6 MHz. Let’s let Br equal 6 MHz too and tau-r = 0.167 microseconds. Then SQRT(tau-r * Br) is 1.0.

Let’s assume a typical television station power of 50,000 watts and assume the worst case, that the signal is isotropic (spread out in all directions). We’ll assume that the signal to noise ratio equals 1.0. Let’s also assume that some kind of supercivilization is picking up the broadcast so the noise temperature of the receiver is almost to the cosmic background noise level of 2.7 deg K (let’s put it as 5 deg K).

Then, what do we have:

Rmax = 1.04E9 * Dr meters

To Be Continued…

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