On Oct. 4th, amateur radio operator Scott Tilley picked up a carrier wave from NASA's Mars Reconnaissance Orbiter (MRO) circling the Red Planet.
The free space path loss is computed with the expression:
dB = 37 dB + 20log(f) + 20log(d)
Here, f is the frequency in MHz and d is the distance in miles.
That says the path loss is 37+ 20log(10,000) + 20log(38.6x106) or 266 dB
Scott Tilley's hobby is looking for satellites. Sometimes presumed dead, sometimes kept hidden. Spaceweather puts it this way:
Tilley is a leader in the field of satellite radio. Dead satellites, zombie satellites, spy satellites: He routinely finds and tracks them. "But this was a first for me," he says. "A satellite around Mars!"
It's not easy picking up radio signals from distant planets. NASA does it using the giant antennas of the Deep Space Network. Tilley uses a modest 60 cm dish in his backyard in Roberts Creek, BC. This week's close encounter with Mars set the stage for his detection.
"MRO's signal is weak, but it is one of the louder signals in Mars orbit," says Tilley. "The spacecraft has a large dish antenna it uses as a relay for other Mars missions. With the proximity of Mars these days, it was the perfect time to try."