On Wed, 16 Jan 2013 19:35:02 +0100, Leif Neland
wrote:

Michael A. Terrell skrev:
wrote:

Hello,

I live in Canada and I need good (low or no radiation) cordless phone.


How is it supposed to work if it doesn't radiate some RF?

Infrared?

In my checkered past, I designed and built an IR paging system that
never made it to market. That's different from a cordless phone in
that the IR paging path is one way. To cover a rather large office
area, I was running 10 watts of IR into a hemispherical reflector to
get wide area coverage. It also has the problem of only allowing one
conversation (or compressed audio time slice) at a time per room. No
problem for paging, but big problems for IR. Visualize a room full of
TV sets, as found in the department stores, and expecting all the
remote controls to run simultaneously at the same time. I could have
used different "colors" of IR to get more than one channel, but the
filters are pricy. The spec was for 100 channels with 205
utilization, which means 20 different "colors". That won't happen.

To go bidirectional, I would need at least several hundred milliwatts
of IR in the handset, or less with shorter range. Also add extra
voice compression and switching circuitry, so that it simulates a full
duplex system. Compared to the typical 5mw of RF produced by various
wireless cordless phone systems, IR would be a battery hog.

Dealing with obstructions wasn't much of a problem. IR bounces nicely
off of various objects. Multiple emitters were also a big help.
However, dealing with IR interference from lighting and sunlight
through windows was not much fun. The light from these would overload
the receive phototransistor resulting in a very high baseline noise
level, which the emitter had to overcome. That's another reason why I
needed 10 watts.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558