"JJ" wrote in message
...
Harris wrote:
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.

So you don't need a LOT of power to contact Mars.

It takes lots of ERP (Effective Radiated Power). You can get high ERP by
using high power or a high gain antenna (or both). The 12-foot dish on
Voyager has over 40 dB of gain at X Band. In conjuction with Voyager's 20
watt (not 2 watt) transmitter, that produced over 200,000 watts of ERP.

See:
http://www.spacetoday.org/SolSys/Voyagers20years.html


The statement I took issue with was:

"Very little power is necessary in space. I had a QSO with an astronaut on
MIR with a 3 watt ht. With nothing in the way, it will go on virtually
forever."

That implied that a simple low power transceiver and mediocre antenna could
communicate over unlimited distances in space. That is simply not true. The
Mars missions and Voyager mission used very sophisticated engineering to
accomplish what they did.

Art N2AH