Can cell phones and SPS share the same frequency?

Let's assume that SPS is beaming down microwaves at 900 W/m^2 intensity in a
column of focused energy 10 km in diameter at a frequency of 2.45 GHz.

The rectenna will be a contiguous section of land with limited dual use
capacity.

How far away would the interference from this beam travel?

What provisions could be undertaken to minimize cell phone disruptions? What
other uses are reserved for this frequency range?

Do cell phone signals bounce off of the ionosphere (?) or are they pretty
much point to point transmissions from one tower to the next?

If needed could frequency shifting occur near a rectenna and then be shifted
back to the original frequency?

Any insight into this issue would be appreciated?

TangoMan

In article 6Cgwb.481120$pl3.23599@pd7tw3no,
TangoMan wrote:
Let's assume that SPS is beaming down microwaves at 900 W/m^2 intensity in a
column of focused energy 10 km in diameter at a frequency of 2.45 GHz...
How far away would the interference from this beam travel?

Depends on what you define as "interference". Especially if powersats
(and hence their beams) are widespread, it's going to make other uses of
that band problematic. The beam power isn't *entirely* confined to the
main beam; it comes very close to being completely confined, given the
size of the transmitting antennas, but not quite, and the power output is
so enormous that even trifling leakage is an issue.

This once was no big deal, since that was an "industrial/scientific/medical"
band not used for communications.

(There would be some problems in nearby bands as well. Not huge ones, but
quite possibly requiring changes to equipment. Just what constitutes an
"adequately selective" filter in a receiver front-end will change with
that much RF power being thrown around in a nearby band.)

What provisions could be undertaken to minimize cell phone disruptions? What
other uses are reserved for this frequency range?

Unless I've missed something, there are no cell phones at 2.45 GHz. They
have their own band, elsewhere.

What *does* show up at 2.45 GHz, these days, is various new communications
applications -- wireless networking in particular -- plus some old ones
looking for a new home, like the links between cordless phones and their
base units.

Communications uses of that band are essentially "use at your own risk",
so technically none of those services can object if they're blasted off
the air by a new application, especially an industrial application which
fits the nominal use of the band better. Which doesn't mean there
wouldn't be a whole lot of unhappy customers...

Do cell phone signals bounce off of the ionosphere (?) or are they pretty
much point to point transmissions from one tower to the next?

The whole idea of cell phones is that their transmissions are just strong
enough to reach the nearest tower, the one that serves the particular
"cell" they are in. The towers do not use radio to talk to each other.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

" Do cell phone signals bounce off of the ionosphere (?) or are they
pretty
much point to point transmissions from one tower to the next?

The whole idea of cell phones is that their transmissions are just strong
enough to reach the nearest tower, the one that serves the particular
"cell" they are in. The towers do not use radio to talk to each other.

Sorry. I muddled the question. I meant to the towers use a bounce to
transmit to other towers. You've answered the question. I assume towers
connect into the main trunks to transmit to the final tower.

How powerful is 900 W/m^2 compared to other radio frequency users in other
bands? Military radar, TV, radio, etc.

Do you have any idea on much leakage there would be from the SPS beam and
how far from the beam that leakage would impact other users?

What prompted my question was the realization that the beam would be in a
discreet zone aimed to each rectenna. If every rectenna was rated at 5 or 10
GW, then rectenna wouldn't be a dime a dozen and perhaps there could be an
exclusion zone for the frequency just around the rectenna sites.

Can the above thinking be advanced in any fashion to a useful proposition?

TangoMan

In article VLEwb.493913$9l5.333920@pd7tw2no,
TangoMan wrote:
How powerful is 900 W/m^2 compared to other radio frequency users in other
bands? Military radar, TV, radio, etc.

The fast answer is, a whole bunch. :-)

900 watts is a hefty transmitter for non-broadcast communication uses --
that's 900 watts *total*, spread over thousands of square kilometers even
if it's at a frequency that is strictly line-of-sight, giving power levels
at the receivers down in the nanowatts per square meter at best.

Big broadcast transmitters can be up around a megawatt, if memory serves,
but they're also covering substantially larger areas (which is why they
want very tall antennas). People living near those can have problems with
more distant stations on nearby frequencies being drowned out, especially
on cheap receivers.

I think big fixed radars can also be up in that range of power output, and
there things are a bit more complicated because of relatively narrow
beams. Right in front of the antenna, they may be comparable. At any
distance, much less.

Powersats are really in a category by themselves.

Do you have any idea on much leakage there would be from the SPS beam and
how far from the beam that leakage would impact other users?

I know this *has* been looked at in some depth, but I'm not familiar with
the details. Rough guess: effects would be most conspicuous in an area
around the rectenna, probably many kilometers wide, but there would be
lesser leakage covering whole regions.

What prompted my question was the realization that the beam would be in a
discreet zone aimed to each rectenna. If every rectenna was rated at 5 or 10
GW, then rectenna wouldn't be a dime a dozen and perhaps there could be an
exclusion zone for the frequency just around the rectenna sites.

I think the beam frequency itself is just going to have to be reserved for
powersat use and nothing else, on at least a continental scale. The main
question is impact on nearby frequencies, and the worst forms of that are
likely to be more localized.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article VLEwb.493913$9l5.333920@pd7tw2no,
TangoMan wrote:
How powerful is 900 W/m^2 compared to other radio frequency users in other
bands? Military radar, TV, radio, etc.

The fast answer is, a whole bunch. :-)

900 watts is a hefty transmitter for non-broadcast communication uses --
that's 900 watts *total*, spread over thousands of square kilometers even
if it's at a frequency that is strictly line-of-sight, giving power levels
at the receivers down in the nanowatts per square meter at best.

Big broadcast transmitters can be up around a megawatt, if memory serves,
but they're also covering substantially larger areas (which is why they
want very tall antennas). People living near those can have problems with
more distant stations on nearby frequencies being drowned out, especially
on cheap receivers.

I think big fixed radars can also be up in that range of power output, and
there things are a bit more complicated because of relatively narrow
beams. Right in front of the antenna, they may be comparable. At any
distance, much less.

Powersats are really in a category by themselves.

Do you have any idea on much leakage there would be from the SPS beam and
how far from the beam that leakage would impact other users?

I know this *has* been looked at in some depth, but I'm not familiar with
the details. Rough guess: effects would be most conspicuous in an area
around the rectenna, probably many kilometers wide, but there would be
lesser leakage covering whole regions.

What prompted my question was the realization that the beam would be in a
discreet zone aimed to each rectenna. If every rectenna was rated at 5 or 10
GW, then rectenna wouldn't be a dime a dozen and perhaps there could be an
exclusion zone for the frequency just around the rectenna sites.

I think the beam frequency itself is just going to have to be reserved for
powersat use and nothing else, on at least a continental scale. The main
question is impact on nearby frequencies, and the worst forms of that are
likely to be more localized.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

TangoMan wrote:

[snip]

What provisions could be undertaken to minimize cell phone disruptions? What
other uses are reserved for this frequency range?

Wireless networks, for one....

Do cell phone signals bounce off of the ionosphere (?)

No. Once you get above about 30 megahertz, this almost never happens.
(there are some other interesting unusual propogation modes at VHF and
UHF, but that's another matter)

or are they pretty
much point to point transmissions from one tower to the next?

Yes. Not much more than line of sight.

And that's by design. It allows you to re-use the same frequency in
an area not very far away (another 'cell'), without interference. This
is why you don't want to use a cellphone in an aircraft (in addition to
possible interference with the plane's instruments). At tens of
thousands of feet, you're now in line of sight of *many* cell towers,
and things can get very confusing....


--

You know what to remove, to reply....

TangoMan wrote:

[snip]

What provisions could be undertaken to minimize cell phone disruptions? What
other uses are reserved for this frequency range?

Wireless networks, for one....

Do cell phone signals bounce off of the ionosphere (?)

No. Once you get above about 30 megahertz, this almost never happens.
(there are some other interesting unusual propogation modes at VHF and
UHF, but that's another matter)

or are they pretty
much point to point transmissions from one tower to the next?

Yes. Not much more than line of sight.

And that's by design. It allows you to re-use the same frequency in
an area not very far away (another 'cell'), without interference. This
is why you don't want to use a cellphone in an aircraft (in addition to
possible interference with the plane's instruments). At tens of
thousands of feet, you're now in line of sight of *many* cell towers,
and things can get very confusing....


--

You know what to remove, to reply....

TangoMan wrote:


The whole idea of cell phones is that their transmissions are just strong
enough to reach the nearest tower, the one that serves the particular
"cell" they are in. The towers do not use radio to talk to each other.

Sorry. I muddled the question. I meant to the towers use a bounce to
transmit to other towers. You've answered the question. I assume towers
connect into the main trunks to transmit to the final tower.

No, each tower has its own landline connection to the telephone
central offices (switching stations).

There have been places (espically after major power disruption in
Chicago, some years back) when cellphone sales went up, as people
assumed they'd still have service in the next such power failure. The
blackout of last August showed them, however, that even if their phone
is fully charged, if they're not in range of a cell tower whose
transcievers and other electronics have power (the landline system has
its own backup power), they're still out of luck. Their phones have
nothing to talk to.

(I'm reminded of a scene in the movie 'Six Days, Seven Nights.' Only a
satphone would've helped Anne Hecht...)


--

You know what to remove, to reply....

TangoMan wrote:


The whole idea of cell phones is that their transmissions are just strong
enough to reach the nearest tower, the one that serves the particular
"cell" they are in. The towers do not use radio to talk to each other.

Sorry. I muddled the question. I meant to the towers use a bounce to
transmit to other towers. You've answered the question. I assume towers
connect into the main trunks to transmit to the final tower.

No, each tower has its own landline connection to the telephone
central offices (switching stations).

There have been places (espically after major power disruption in
Chicago, some years back) when cellphone sales went up, as people
assumed they'd still have service in the next such power failure. The
blackout of last August showed them, however, that even if their phone
is fully charged, if they're not in range of a cell tower whose
transcievers and other electronics have power (the landline system has
its own backup power), they're still out of luck. Their phones have
nothing to talk to.

(I'm reminded of a scene in the movie 'Six Days, Seven Nights.' Only a
satphone would've helped Anne Hecht...)


--

You know what to remove, to reply....

In article , Joann Evans wrote:

There have been places (espically after major power disruption in
Chicago, some years back) when cellphone sales went up, as people
assumed they'd still have service in the next such power failure. The
blackout of last August showed them, however, that even if their phone
is fully charged, if they're not in range of a cell tower whose
transcievers and other electronics have power (the landline system has
its own backup power), they're still out of luck. Their phones have
nothing to talk to.

And, of course - especially in urban areas - cells can swamp. A sudden
surge of traffic, a lot of people in a restricted area all deciding they
need to use a cellphone at once, and bang a lot of them are looking at a
silent network.

(This can be spotted reasonably easily, in Civilised Parts, by trying to
call out at about 00.10 on January 1st from your nearest urban
centre...)

One of the things which will cause this, of course, is something like a
major blackout...

(Do the US providers have something like the limited preference-system
we have here? A list of numbers, generally belonging to technical staff,
which are bounced to the top of the list in an overlogged cell...)

(I'm reminded of a scene in the movie 'Six Days, Seven Nights.' Only a
satphone would've helped Anne Hecht...)

Heh. One of the things I can't help but be amused by is encountering
novels, generally sf from the 1970s, where the entire plot manages to be
invalidated by no-one predicting any kind of mobile phone. C'est la vie,
I suppose...

--
-Andrew Gray