Arthur Harris wrote:
"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.

The Voyager's power is now down to 2 watts and has been for some time to
conserve power. So you don't need a LOT of power to communicate long
distances in space. Real power from the transmitter and ERP are two
different things.