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TUCoPS :: Radio :: cordinfo.txt

Cordless Phone Info

On Cordless Phone Reception

   Cordless phones all employ at LEAST two universal frequencies - one for the
base unit to communicate to the handset with various data (46.6 - 47 MHz),
which performs all functions. This, the 46 MHz frequency, carries incoming
signals from the phone line (dial tone, the CALLER's voice, and the user of the
cordless phone's voice as well since it is directed back TO the handset as a
voice is in a standard telephone). The handset operates in conjunction with the
base unit and uses the 49.6 - 50 MHz to transmit back to the base, and only
transmits the user's voice and the numbers that the user dials. It is possible
in the monitoring of these frequencies that you may be too far away to hear a
user's base unit, yet the handset may come in clear, or vice-versa. Then again
if you can hear the base unit fine, the user's handset frequency may be
occupied by a nearby baby or room monitor and get clobbered altogether.
   So now you know that a cordless phone utilizes at least two frequencies.
That is all that even the SIMPLEST phone needs to operate. But, get this: since
there are TEN POSSIBLE CHANNELS, that is, TWENTY FREQUENCIES in all, you'd get
lost if there weren't something halfway universal about this whole operation.
Apparently, so would the manufacturers. There is, fortunately, a coordination
of frequencies between base and handset, and they are categorized by channel:

Channel  Base    Handset
-------  ----    -------
   1     46.610  49.670
   2     46.630  49.845
   3     46.670  49.860
   4     46.710  49.770
   5     46.730  49.875
   6     46.770  48.830
   7     46.830  49.890
   8     46.870  49.930
   9     46.930  49.990
  10     46.970  49.970

   So, some lazy phone manufacturer wasn't just standing around tossing coins
one day deciding, "This Channel 10 phone's handset is going to be on one
frequency, and this channel 10's handset is going to be on something ELSE". At
first, I thought that any handset frequency could be used with any base channel
the manufacturer wanted.
   Something else, too. Don't be surprised if you hear a cordless conversation
on one base channel, and on the next conversation you hear the same person
talking on ANOTHER channel. Some phones are switchable between frequency pairs.
It did catch ME by surprise when I first heard this, not being 100% familiar
with all types of cordless phones. My first reaction was, "that woman must be
loaded and have a cordless in every room. That's about 5 frequencies I've heard
her talking on..." when in reality, she may only have one or two. Radio Shack
advertises at least one type of phone that allows a caller to push a button on
the phone - even during a conversation - to change channel for clearest
possible reception.
   It also boasts that it has a fully automatic 640,000-combination security
code making it virtually impossible for another cordless phone to access the
line. This probably has no effect on a scanner buff's ability to HEAR the
conversation. One other cordless phone, specifically made by Radio Shack, has a
cordless cradle where it would normally plug into the wall, then the handset is
corded to the cradle which includes the keypad. It operates on three size "C"
batteries and boasts that it can be used on coffee tables, or areas where wires
would probably be in the way.
   So, it's obvious that there are now a multitude of cordless phones "out
there" that are available to consumers, and the more different types and
appealing styles there are, the more you'll probably be hearing. Personally I
smile at the AT&T Cordless "talking in a tin can" TV commercial when it comes
on, and say, "yeah, sell more of those so I can listen to you..."
   I too have a cordless phone, but I don't use it as often anymore. I wonder
if the new instructions enclosed with cordlesses have a statement, "privacy on
this phone is not guaranteed.."

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