Subj : Re: Mars bounce
To   : alt.ham-radio.vhf-uhf
From : Bob Bob
Date : Sat Oct 15 2005 15:54:19

From Newsgroup: alt.ham-radio.vhf-uhf

Once again work out the maths. The earth station will obviously have 
oodles of power and a large high gain dish. They will also have cooled 
receiver front ends.

The spacecraft has a limited power budget but its RX will already be 
super cooled.

As I remember sending pictures from deep space was a lengthy process 
because of the low bandwidth employed, You will find that as the 
spacecraft gets further and further away they only need to reduce the 
bandwidth more and more.

Have a look at free space path loss and start plugging in some real 
numbers. (From ARRL handbook)

Loss in dB = K + 20logf + 20logD
Where f is the freq in GHz and D is the distance in miles
K is a constant of around 96.6dB

If you then took medium performance 2M SSB transceivers at both ends of 
a circuit) of 25W output (say 44dBm) and a receiver usable to 0.08uV 
(-129dBm) then applied coaxial line loss (say -2dB total) and antenna 
gain (say 10dB at each end) of 20dB, that gives you a maximum "loss" 
available for the setup. Plug that into the formula above (reversed) and 
you have the maximum free space distance covered. (loss is 191dB)

Increasing the antenna gain, output power, lowering coaxial loss and 
improving receiver sensitivy will make this margin number larger still.

Go for it!

Cheers Bob VK2YQA

Carl / W6VDC wrote:
>>
> 
> So how the heck does NASA still communicate with Voyager?  How they heck 
> do they discriminate Voyagers singnal from static?  And HOW do Voyager 1 
> and Voyager 2 still communicate with each other???  It boggles my mind.  
> I sure hope NASA never abandons these little guys so far away from home.
>

.