Owen Duffy wrote:
Look up the Friis Transmission equation on Google.

Here is a little application for solving the Friis Transmission equation:
http://www.vk1od.net/software/fsc/ .


Andy asks:

The Friis equation at the above website states that the distance
exponent may be a number different than "2".

Can anyone here explain why a number other than "2" could be
used, and under what conditions ??

Thanks,

Andy W4OAH

AndyS wrote:

Andy asks:

The Friis equation at the above website states that the distance
exponent may be a number different than "2".

Can anyone here explain why a number other than "2" could be
used, and under what conditions ??

Thanks,

Andy W4OAH

The exponent of 2 assumes no dissipative path loss. That is, the
reduction in field strength is due solely to the power being spread out
over an area which increases with distance from the source, and not to
any reduction in the total power at any distance. A larger exponent
would be appropriate when the path is lossy, for example when ground
wave attenuation is present. A path through air could also get lossy at
microwave frequencies due to water in the air in liquid or gas form, and
at extremely high frequencies due to absorption by various atmospheric
gases.

Roy Lewallen, W7EL

AndyS wrote in
:



Owen Duffy wrote:
Look up the Friis Transmission equation on Google.

Here is a little application for solving the Friis Transmission
equation: http://www.vk1od.net/software/fsc/ .


Andy asks:

The Friis equation at the above website states that the distance
exponent may be a number different than "2".

I don't think I say that, Friis uses an exponent of 2, but the calculator
can also solve the equation with an exponent other than 2.

Can anyone here explain why a number other than "2" could be
used, and under what conditions ??

An example is that the FCC stipulates exponents of other than 2 for some
field strength interpolation / extrapolation, up to 4 IIRC, and this is
for application in real situations at closer distances than radiation far
field conditions.

The use of the exponent is to account for some other effects. In some
cases the value of the exponent has been challenged. If I understand the
case correctly, the ARRL has challenged some instances used for BPL and
the court has required the FCC to scientifically substantiate its
exponent, or use another which it can scientifically substantiate.

The ability to specify the exponent is principally provided for peforming
those interpolation / extrapolations.

Owen


Thanks,

Andy W4OAH