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Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!ihu1h!parnass
From: parnass@ihu1h.UUCP (Bob Parnass, AJ9S)
Newsgroups: net.ham-radio
Subject: Re: Commercial FM "tweedle"
Message-ID: <621@ihu1h.UUCP>
Date: Sat, 6-Jul-85 02:18:51 EDT
Article-I.D.: ihu1h.621
Posted: Sat Jul  6 02:18:51 1985
Date-Received: Sun, 7-Jul-85 05:46:08 EDT
References: <85@biomed.UUCP>
Organization: AT&T Bell Laboratories
Lines: 29

>	  Living around	Boston,	I have heard several walkie-talkies that the
> transit police carry and also	the EMS	ambulance people.  They	all seem to be
> Motorolas.  Anyway, it seems that when the base station releases its mike
> key, a couple	of single tones	are transmitted, very rapidly, one after
> another, each	about 100mS long, with no space	in between them, the first
> tone higher in freq than the other.  One is about 1.5kHz and the other a bit
> lower, maybe around 1kHz.  WHAT are these for?
>
> All comments appreciated.
> N 1 A	L G    Bobby L.

     I think what you heard are	the tone  signals  generated
     by	the remote control unit	located	at the base operator
     position.	This control unit is probably connected	 via
     dedicated "phone" lines to	the actual transmitter.

     Since these "phone" lines have no DC  continuity,	tone
     signals  are  used	 to remotely control the transmitter
     (e.g.  transmit,	receive,   change   channel,   etc).
     Although  these  tones  are  supposed  to	be  muted to
     prevent their  transmission  over	the  air,  it's	 not
     uncommon to hear them "slip out".

     I hear these tones	on the Bolingbrook (IL)	Police	base
     on	 155.250  MHz,	and the	Illinois Department of Tran-
     sportation	on 151.100 MHz.
-- 
===============================================================================
Bob Parnass,  Bell Telephone Laboratories - ihnp4!ihu1h!parnass - (312)979-5414