[Antennas] Signal loss (path loss)

Mon Aug 27 22:24:38 EDT 2007

 
-----Original Message-----
From: Eric Lemmon [mailto:wb6fly at verizon.net] 
Sent: Monday, August 27, 2007 6:04 PM
To: 'A10382'
Subject: RE: [Antennas] Signal loss (path loss)
Let's be very careful to separate any calculations for interstellar
transmission from calculations for terrestrial transmission. To state that
they are NOT THE SAME is an understatement! It is very true that low-power
transmissions from interstellar spacecraft can be received on Earth with the
appropriate equipment, but that is irrelevant to point-to-point links here
on Terra Firma.
Without going into the minutiae of the calculations, the fact that the Earth
is round means that propagation by diffraction and reflection must be
considered and added to simple free-space loss, as must losses created by
propagation through the Fresnel Zone. Moreover, the calculation of
propagation losses is not simple, but neither is it impossible.
I urge any readers of this thread to download the following Datafiles from
the Repeater-Builder site:
<www.repeater-builder.com/ge/datafile-bulletin/df-10003-01.pdf>
<www.repeater-builder.com/ge/datafile-bulletin/df-10003-03.pdf>
<www.repeater-builder.com/ge/datafile-bulletin/ecp-159.pdf>
General Electric engineers spent a lot of time trying to make complex
calculations simpler, so that guys and gals like us could put those
calculations to use and come up with credible results. Let's take advantage
of this resource!
73, Eric Lemmon WB6FLY
-----Original Message-----
From: antennas-bounces at mailman.qth.net
[mailto:antennas-bounces at mailman.qth.net] On Behalf Of A10382
Sent: Monday, August 27, 2007 11:57 AM
To: Antennas at mailman.qth.net
Subject: [Antennas] Signal loss (path loss)
For those of you that like to calculate radio propagation:
The electro-magnetic strength of an rf signal decreases the further you get 
from the transmitting antenna.
The formula, which is simple, escapes me at the moment.
We usually think (and calculate) in terms of miles (or even hundreds and 
thousands of miles).
Think of the path loss of a signal for the following distance:
 7.9 BILLION MILES !
The spacecraft Voyager was launched quite a few years ago to research the 
cosmos. It is still sending back usable data that is received by NASA - and
now it's about 7.9 BILLION miles from earth.
Even if the transmitter is operating at 100W (Voyager is totally solar 
powered and solar energy also decreases the further you get from the Sun). 
The signal strength that finally reaches the antenna here on earth must be 
tiny - to say the least ! The 'gain (focus) at both ends has to be 
tremendous and the receiver extremely sensitive. The frequency used must be 
one that has a very low noise floor and is one not widely used by other 
naturally occurring items.
If anyone has the path loss formulae handy, they would be appreciated.
============
______________________________________________________________
Antennas mailing list
Home: http://mailman.qth.net/mailman/listinfo/antennas
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:Antennas at mailman.qth.net