TELECOM Digest OnLine - Sorted: Re: Cell Phone Extenders?

Re: Cell Phone Extenders?

Michael D. Sullivan (userid@camsul.example.invalid)
Sat, 31 Dec 2005 07:48:07 GMT

> [TELECOM Digest Editor's Note: But if you buy a cell phone and obtain
> service from some carrier, aren't you granted a license (on the
> carrier's master license) to use the phone as a transmitter? PAT]

If you buy a cellphone and contract for service for that cellphone
with a licensed carrier, then that carrier's license covers the
operation of the phone you activated with that carrier. You can't
then go out and use other phones under that contract without the
carrier's consent. Likewise, you can't just build a new cellsite,
operating on the carrier's frequencies, to provide coverage to your
phone in an area (e.g., your entire city, neighborhood, backyard,
basement, or office) where the carrier's network doesn't have a good
signal. You have to have a license to build a base station or
repeater, or an agreement with the licensee(s) whose signal will be
transmitted that allows you to use their frequencies.

An "enhancer", "booster", or "repeater" is a transmitter (it may be
configured as a broadband receiver and linear amplifier, but it's
still a transmitter). If it isn't very low power and compliant with
Part 15 limits, it requires a license, for good reason. Even well
engineered, professionally installed transmitters can cause
interference, either to other parts of the same network or to other
networks. When interference occurs to the same network, the
interference can be managed, because the engineers can tweak the power
levels and frequencies of the various transmitters under their control
to minimize the effects of the interference or cause users to operate
on specific frequencies in given areas. An independently operated
transmitter or "booster" of more than minimal signal strength in the
same band that "repeats" the signal received at a given location
without the carrier's knowledge or consent can wreak havoc on signal
quality for other users without the network engineers being able to
manage it. Yeah, Joe Blow gets a better signal in his back yard, but
causes service to suck elsewhere in the area, and the carrier can't
fix it unless they find out who's got the unlicensed transmitter and
make the owner turn it off.

As I mentioned, even a well-installed transmitter under the carrier's
control can cause interference to other networks, and obviously an
independently installed transmitter may also cause interference of one
sort or another out of band, especially since it won't be manufactured
and installed to the same specs as a carrier's network equipment.
There are any number of reasons for this, ranging from intermodulation
products to desensitization of licensed transceivers. But if
interference occurs to a police radio from what appears to be a
cellular or SMR tranmsission, the FCC is going to look to the cellular
or SMR operator to fix it -- but they can't fix problems caused by
third parties using illegal cell boosters. They may have to turn down
or turn off cellsites serving thousands of users, not knowing that the
problem was caused by an illegal booster. Or the interference may be
traced to a particular location by the FCC or the interfered-with
party and the carrier is then requested to fix the interference, only
to inform them that the carrier doesn't operate a cell at that
location. This has actually happened.

Michael D. Sullivan
Bethesda, MD (USA)
(Replace "example.invalid" with "com" in my address.)

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