Thus spake Jim Lesurf:
Snipped
Indeed, you may recall some 'health scares' about TETRA that were
fuelled by its pulse profile - although those who panicked at the
time had the details wrong so were worrying about nothing much. If
interested, have
a look at

http://www.st-and.demon.co.uk/temp/tetra.html

Note that although the base stations probably don't normally pulse,
the mobiles probably do, both to save energy and to reduce slot
conflicts.
The point of the above page was to show that 'health' worries about
the *base stations* was probably groundless. Locally, we had all kinds
of stories about 'Cows not giving milk', etc, when TETRA bases were
installed - in fact before they came into actual acive use. :-)

A friend was using Tetra radios as a constable on his beat in Skegness more
or less from launch. He reported no personal health issues but related
several anecdotal stories of scrambled brains. IIRC, the poorest aspect was
the pass-through onto the mobile network wasn't brilliant therefore was
easier to use his mobile.

A distinction to be made is one that (surprisingly) in my experience
often escapes people in the military, etc, who deal with encrypted or
spread spectrum comms. The payload data may be unreadable, but the
actual signals are easily detected, and often easily indentified in
terms of class of system. Alas, it seems easy for people to assume
that the information being encrypted as being the same as the actual
transmission being undetectable. Tain't so.

For the above reason you could, if you wished, easily detect when the
Bill are transmitting and even say where from... Technically, not
particularly difficult. Indeed, I've done this sort of thing for
other (legal) reasons in the past... :-) Knowing what they are
saying would be more difficult.

For similar reasons, locating, jamming, etc, of mobiles is much
easier than actually listening to the message payload/content.

The current use of the radio spectrum of allocating certain frequencies to
particular purposes makes it a no-brainer to know if that band is in use.
However, if UWB/SDR/Cognitive Radio ever reaches the ether, it will be
virtually impossible or very difficult to pull out military, emergency,
mobile, TV etc, etc from one another, ever before one can even contemplate
decrypting anything. If CR ever happens, it will be incremental, probably
with holes all through the spectrum for non-hopping radio. I can't see a
future humble radio hopping from DC to light either - just too expensive for
the intended purpose. Propagation characteristics are hardly even from DC to
light either. It will certainly make the whole spectrum a hell of a lot more
efficient, once regulators & the military can grasp the concept of loosing
fixed bands but retaining priority of use, security etc

--
Basically, I hate people who preface nearly every sentence with the word
'basically'!