Re: Tunnel Radio (was reception)

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Article #966

#966

From: David I. Emery
Date: Tue, 25 Jul 1989 21:07

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In article <1566@unccvax.UUCP> dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) writes:
>
>	[The Lincoln Tunnel authorities can break into...]
>> normal re-broadcast for emergency messages.  They do this, I believe, on
>> every AM channel.
>
>	Does anyone know exactly **how** they accomplish this? The
>"every AM channel" system is used in Boston (in the sort-of-tunnel
>under Copley, and in the Callahan and Sumner tunnels)....
>
>	I suspect that it is spread spectrum (of sorts) which hits
>(swept) from 530 to 1600 kHz every 100 uS or so.


	My understanding is that done with a comb generator driven by
10 khz which produces harmonics every 10 khz.  The relevent ones are
selected with a bandpass filter that passes the AM band and then modulated
with a balanced modulator carrying the AM audio.  This effectively AM
modulates every line in the comb.

	The signal is then amplified in a linear amplifier for distribution.



-- 
	David I. Emery   Clearpoint Research Corp. 
	35 Parkwood Dr, Hopkinton Ma. 01748  1-508-435-7462
	{decvax, cybvax0, mirror}!frog!cpoint!die 
	{m2c}!jjmhome!cpoint!die

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References: <Jul.19.14.48.15.1989.439@athos.rutgers.edu> <81@vax87.auc.dk> <3890@phri.UUCP> <1566@unccvax.UUCP>

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!ginosko!husc6!encore!cloud9!jjmhome!cpoint!die
From: die@cpoint.UUCP (David I. Emery)
Newsgroups: sci.electronics,rec.ham-radio
Subject: Re: Tunnel Radio (was reception)
Summary: comb
Message-ID: <2463@cpoint.UUCP>
Date: 25 Jul 89 21:07:51 GMT
References: <Jul.19.14.48.15.1989.439@athos.rutgers.edu> <81@vax87.auc.dk> <3890@phri.UUCP> <1566@unccvax.UUCP>
Reply-To: die@cpoint.UUCP (David I. Emery)
Organization: Clearpoint Research Corp., Hopkinton Mass.
Lines: 29

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