g <wh@t.me.worry> wrote:
> 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.
[...]
> "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.

Yes, this is correct, the frequency-dependent component of free space
path loss is really just a fiction. It is, however, a useful fiction
since it lets you talk about path losses and antenna gains (over isotropic)
as if they were independent issues instead of just a single issue related
to how antennas work.

> 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.

This is true, though it is probably worth pointing out that the limiting
direction for mobile phones is not the tower->handset direction, but
rather the handset->tower direction. The power output from the handset
is limited, and while the power output from the tower is not the reciprocal
performance of the antenna/path/antenna system means that increasing the
power output from the tower much beyond that of handset doesn't help.

As for path attenuation, while this might be academically interesting
to know it doesn't, by itself, tell you what is of greater practical
interest, which is how well the system performs.

>> 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?

I don't, but I'm not sure I care either since, while measuring path
attenuation by itself might be interesting to me personally, what
most people care about is system performance. I.e. does my mobile
phone get service. Given equal output power from the handsets
on both frequencies (almost certain to be true if they're the
same model of handset and you are at the edge of the service
area where they'll be running maximum power), this depends on
the performance of the antenna/path/antenna system, as a unit, that
real engineers can build given the real constraints of designing
for real handsets and real base stations. And, in practice, I
can't find a big difference between the frequencies.

I will admit that I don't know enough about the topic to preclude
there being practical advantages to be had at 850 MHz over
1900 MHz for mobile phones; I'm sure there are based on the
band choices rural phone companies seem to make when establishing
service in previously unserved areas. What I do know, however, is that
this advantage is nowhere near the 7 db, 2x distance being claimed
based solely on free space path loss, in practice because I could
certainly measure a difference like this at my house, and in
theory since talking about frequency-dependent free space path loss
without talking about (the intimately related issue of) frequency-dependent
antenna performance makes no sense as an argument.

Dennis Ferguson