Fred,

In the USA, by law scanners must not be capable of receiving cellular
telephone frequencies, so they are generally "blocked"; that is, the
microprocessor does not allow those frequencies to be tuned in. Usually the
same models of scanners are available for purchase outside the US, but
without the specific frequency blocking. Although illegal, it is possible
to have these unblocked scanners shipped into the US from sources outside
the US.

You would want an unblocked scanner if you want to monitor cell phones
(which is illegal in the US). Unfortunately, much (but not all) of the cell
phone communication is now digital, which is impossible to decode using any
scanner sold anywhere--you need special equipment generally only available
to cell phone companies and government agencies, etc.

There are also some cases (such as with some Yaesu receivers, among others),
where the scanners block some frequencies outside the actual cellular range
in order to prevent images of cell frequencies (intermediate and usually
undesirable signals resulting from the demodulation process inside the
receiver) from being picked up as well. Sometimes those additional (legally
monitorable) frequencies carry signals that some people want to monitor, so
they seek unblocked receivers to enable that. So it's not always for
reasons of illegal cell phone monitoring that unblocked models are sought
(but usually it is).

- Doug


"Fred" wrote in message
. ..
Forgive me because I'm a complete novice but, what is an unblocked scanner
and why would I want one?