JJ wrote:
Arthur Harris wrote:

The signal will decrease by 6 dB every time you double the distance. MIR was
about 250 miles above Earth, and you could establish communicaion with
fairly low power when it was overhead. On the other hand, Mars is about 35
million miles away! You'd need a LOT more power and antenna gain to contact
Mars.


Voyager 1 is just over 90 Astronomical Units or 8.4 billion miles from
the sun, transmitting with approximately 2 watts and signals are still
being received here on earth. How do you account for that?

A steerable 12-foot dish on the spacecraft, and HUGE antenna arrays on
Earth.

See:
http://www.spectrum.ieee.org/pubs/tr...c06-stone.html

The article says in part:

"The science data from this 12-year journey of exploration completely
altered our understanding of these planetary systems. A number of
first-time telecommunications achievements made this possible, including
the first operational X-band (8.4-GHz) system. During the course of the
mission, there were a number of significant changes to the communications
system on the spacecraft and on Earth which provided in aggregate a factor
of six higher data return at Neptune than was possible at launch. Data
compression programmed into the flight data system gave the largest single
increment, and switching from a Golay code to a Reed-Solomon code helped
enable the use of the data compression. The other major contribution came
from increases in effective receiving area by arraying of multiple Deep
Space Network (DSN) antennas and increasing the size and efficiency of the
largest DSN antennas from 64 m to 70 m. For the Neptune encounter, an
array of 29 antennas consisting of 70- and 34-m antennas in California and
27 additional 25-m antennas (comprising the National Science Foundation's
Very Large Array in New Mexico) provided fully steerable equivalent
aperture of 150 m."

Art N2AH