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From: mikey@trsvax.UUCP
Newsgroups: net.micro
Subject: Re: BRS home controllers and Cordless Ph - (nf)
Message-ID: <53400026@trsvax.UUCP>
Date: Tue, 15-May-84 10:12:00 EDT
Article-I.D.: trsvax.53400026
Posted: Tue May 15 10:12:00 1984
Date-Received: Fri, 18-May-84 01:43:19 EDT
References: <2421@ecsvax.UUCP>
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Nf-ID: #R:ecsvax:-242100:trsvax:53400026:000:1667
Nf-From: trsvax!mikey    May 15 09:12:00 1984

#R:ecsvax:-242100:trsvax:53400026:000:1667
trsvax!mikey    May 15 09:12:00 1984



MOST cordless phones use the AC line to communicate to the handset.  Until
a very recent FCC change, they used a carrier just above the AM broadcast
band.  BTW, the base to handset is usually AM and the handset to base is FM
just below 50 mhz.  The new FCC policy allows both directions to be FM and in
the 49 mhz range.

Being AM to the handset is not necessarily that bad.  The person on the other 
end still gets a really clean signal, although you don't, and unless they hear
the lawn mower or something, they can't tell your wireless.  Besides,
they were a relatively cheap status symbol.

I don't know if the phone manufacturers were actually restricted from using
FM at 49 mhz before both ways.  It's just that the number of channels were
severly restricted (i.e. 5 or 6) and manufacturers designed their phones
to get the least interference with one another.  Besides, when they first came
out, no one thought they would take off like they did.  

As for interference with BSR controllers, the BSR  puts its
signals on the AC line only at zero crossing, and I seem to remember that 
it had something to do with a 500 khz carrier, but I may be wrong there.
Radio Shack's controller that hooked up to the TRS-80 cassette port still
has a service manual available through their National Parts department.  I
looked at one and it used the same circuitry to couple to the AC line that
some of the intercomes used that had carriers at 500 khz or nearby.  If 
you're interested, you could order a copy of the service manual, but it
won't have information on the actual protcall for the controllers, just
technical informantion on the interface.


mikey at trsvax