[url=http://www.cplire.ru/html/ra&sr/irm/limitations.html]Limitations on Volume of Interstellar Radio Messages[/url]

was shown that real-time digital transmission of audio is not possible:

>If we assume that They are situated in the neighbourhood at a distance
> of 70 light years from us and have the same, or even a little more
>sensitive, SETI receivers, like to our future ATA (Allen Telescope Array)
>or SKA (Square Kilometer Array), then daily volumes of IRMs, which we
>can transmit from ART, GSSR, and EPR toward given celestial target are
> equal 75, 200, and 20 kilobits for ATA-like receiver, or 7.5, 20, and 2
>megabits for SKA-like receiver, respectively. And this volume is in
>inverse proportional dependence from squared distance. Consequently,
>we should aspire to be laconic now in our IRM compositions.

They *do* have tracking on the DSN. How else to they talk to those spacecraft in the ecliptic (not so far from th equatorial plane)?

SETI should try some real feasibility experiments. Take two groups, independent of each other, the other one devises a radio message that should be able to picked up anywhere on Earth with sensitive enough radio equipment (and it should be as vague as that). The other group is the receiver, who don’t know when (let’s say, within a year) the signal begins or ends, at what bandwidth it will be broadcast, or what kind of encoding is used. Neither group knows where the other is located. Basically a double blind STI (Search for Terrestrial Intelligence).

Of course, a certain long distance short wave band (or in any case a band that can be received almost anywhere on Earth, given right circumstances) should be reserved for this purpose for the transmitting group. Now, a certain amount of transmitter time (less than the whole experiment time) should be given to the transmitting team that they can allocate as they choose during the experiment period, while the receiving group listens the whole time using their chosen methods.

If they can detect the signal (and they should of course concentrate on detecting a terrestrial signal sent by the other group, and shifting out all shortwave radio stations etc.) and decode it within that period, it would indicate that it is atleast possible to detect an intelligent message from the noise.