Dennis Ferguson wrote:

> I think this is a bit bogus. I believe the "math" you are considering
> is the path loss alone which, as another post here pointed out, is about
> 7 db greater at 1900 MHz than at 850 MHz.

The "path loss" is constant with frequency if one considers a fixed gain
(electrical size) on one antenna and a fixed aperture (physical size) on
the other. The term 'path loss' was originally used (and misapplied)
modeling links with isotropic antennas at each end. Modeling that way
resulted in constant ERP but diminishing receive antenna aperture. The
result was an apparant loss of signal as frequency increased.
Interestingly, this was probably responsible for commercial and military
users of the radio spectrum considering everything of shorter wavelength
"200 meters and down" fairly useless. Actually though, energy is
conserved and no power is lost on a freespace path; the receive antenna
'bucket size' is just getting smaller with increasing frequency.

To empirically compare path attenuation one needs to know the ERP (which
takes care of both transmit power and sector antenna gain) and handset
antenna aperture.

Your comments about handset antenna differences are valid and without
knowing something about them, it's not possible to make a good
comparison of the effect of frequency on path length by comparing two
phones/systems.

Do note though, there is very solid measured evidence for the component
of attenuation due to frequency alone, as I posted earlier. In addition
to the 20*log(1900/850) 'pathloss' component there is also an absorption
component which truly is related to frequency.


> The same situation exists with cell phones, it is just that since
> I don't know the particular numbers

See above. Sector antennas are normally 10-12 dBi; they have roughly 120
degree beam width azimuthally but can have differing beam widths in
elevation.
Handset antennas are similarly hard to pin down, both due to
inefficiencies due to physical shortening you mention and also due to
ill-controlled polarization and siting errors when used in a typical way.

> And while the above necessarily includes some speculation about how
> it works, what I can tell you for certain that it doesn't seem
> to work your way, with Verizon having this incredible coverage advantage,
> where I live because I did that experiment.

But do you know that the ERP of the two systems was identical and that
the effective aperture of the two handset antennas, as well as the
receiver system temperature were identical?

> In any case, if you want to persist in arguing that 850 MHz provides
> a 2x distance advantage over 1900 MHz, you can't just quote the path loss
> and stop. You've also got to explain why the antenna gains at
> both frequencies would need to be identical, and my understanding of
> the problem leads me to believe you'll have some trouble doing this.

This is certainly true. Since there really isn't any 'path loss' one has
to know a lot about the system in order to measure it. However, this has
been measured extensively over real paths and is the source of COST231,
Lee and other models which do in fact show considerable frequency
dependent attenuation in non-LOS environments.

g