From: jim bell <jimbell@pacifier.com>
Date: Tue, 14 Jan 1997 19:27:44 -0800 (PST)
To: Brad Dolan <michael.tighe@Central.Sun.COM>
Subject: Re: Newt's phone calls
Message-ID: <199701150327.TAA04637@mail.pacifier.com>
MIME-Version: 1.0
Content-Type: text/plain


At 05:56 PM 1/14/97 -0500, Brad Dolan wrote:
>Mmmm.  I'm told that, on most cellphone calls, a scanner will present both
>sides of the conversation on the same frequency.  Usually one side will be
>louder.  Perhaps there's some feedback from a party's receiver back into
>his transmitter?

It's called duplex echo.  Whenever you convert 2-wire audio to 4-wire (two 
pair) you're going to get a reflection.  The cell-phone company can't 
perfectly match the impedances connecting to the local  phonecos, and so a 
little signal gets reflected.  Actually, this is desireable locally because 
it acts as feedback to the speaker, as long as the reflection is kept within 
reason.   The result is that both sides of the communication are hearable in 
the radio signals.

Jim Bell
jimbell@pacifier.com