From that Seti@Home FAQ page:

Table 1 Detection ranges of various EM emissions from Earth and
the Pioneer spacecraft assuming a 305 meter diameter
circular aperture receive antenna, similar to the Arecibo
radio telescope. Assuming snr = 25, twp = Br * Tr = 1,
<eta>r = 0.5, and dr = 305 meters.
-------------+--------------+-----------+--------+--------+-----------+
Source | Frequency | Bandwidth | Tsys | EIRP | Detection |
| Range | (Br) |(Kelvin)| | Range (R) |
-------------+--------------+-----------+--------+--------+-----------+
AM Radio | 530-1605 kHz | 10 kHz | 68E6 | 100 KW | 0.007 AU |
-------------+--------------+-----------+--------+--------+-----------+
FM Radio | 88-108 MHz | 150 kHz | 430 | 5 MW | 5.4 AU |
-------------+--------------+-----------+--------+--------+-----------+
UHF TV | 470-806 MHz | 6 MHz | 50 ? | 5 MW | 2.5 AU |
Picture | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
UHF TV | 470-806 MHz | 0.1 Hz | 50 ? | 5 MW | 0.3 LY |
Carrier | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
WSR-88D | 2.8 GHz | 0.63 MHz | 40 | 32 GW | 0.01 LY |
Weather Radar| | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo | 2.380 GHz | 0.1 Hz | 40 | 22 TW | 720 LY |
S-Band (CW) | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo | 2.380 GHz | 0.1 Hz | 40 | 1 TW | 150 LY |
S-Band (CW) | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo | 2.380 GHz | 0.1 Hz | 40 | 1 GW | 5 LY |
S-Band (CW) | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Pioneer 10 | 2.295 GHz | 1.0 Hz | 40 | 1.6 kW | 120 AU |
Carrier | | | | | |
-------------+--------------+-----------+--------+--------+-----------+

This gives the detectability ranges using the 305 meter Arecibo telescope. The longer distances are for transmissions in tight beams. However, the UHF TV carrier signal is a wider beam and might be detectable. The Arecibo 305 meter telescope could detect it at .3 LY. So a 3 km telescope could detect it at 3 LY and a 10 km wide telescope could detect it at 10 LY.

Bob Clark