Since the publication of my "Servicing of Cordless Phones" in
http://www.elmswood.guernsey.net I have been receiving numerous
enquiries about the typical range of a cordless,the pros and cons of
various frequency ranges etc.Hence this brief article:
Range:
Ancient cordless phones operated at least in one way,using
about 1.8 Mhz,routing the signal through the mains cable itself.
Obviously,this provided maximum range with the attendant penalty:
maximum interference from all mains borne sources.Yet you could
use the phone almost anywhere in the house and the immediate vicinity
with out any regard to the type of construction etc.
The "normal" phones relied on around 47 MHz for their two way
communication (using two different frequencies),which reduced much
of mains borne interfernces,but posed another problem:Mutual interference
from closely built-up communities.Besides some units operated into
the VHF TV channels,which meant broadcasting of your conversation
to your neighbourhood TVs.If you experience undue inteference from
your neighbour's instrument,relocate your base unit.Remember,your
telescopic antenna is carefully chosen to be the most efficient
at its operating frequency - Fully extended -.You can
reduce the range by lowering the telescopic antenna.Use aother
channel,selectable by a small switch both in the handset and the base.
Some recent phones use 900 MHz which means "clear" transmission
with almost no perceptible interference and with the smallest antenna
possible.Good,but there is a flip side:This frequency is attenuated
by some construction materials like steel etc in your building.Though
all high frequencies will be affected by such impediments,this 900 MHz
is affected the most.In addition "the -line -of -sight" propagation
adds to the problem.Location of the base unit is critical and affects
the overall performance of this phones.
Safety
As mentioned earlier,cordless phones put out at the most about
90 dB micro volt or lower,which does not result in any significant
peak RF voltages in the person using it.Compare this with many
Radio Amateur transceivers which belt out peak envelope power in the
regions of several watts.Invariably,they use "external" antennas with
suitable precautions.In light of the past "accumulated data",it is
safe to conclude that there is no danger or threat connected with
the operation of your Cordless.But what comes through them is another
story altogether...
