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Article #4172Re: naive question about RF propagation
From: pierson
Date: Wed, 17 Jan 1990 02:03
Date: Wed, 17 Jan 1990 02:03
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1550 bytes
writes, in part: .. > >Don't (some) subway systems use this so the crew can use radios? >-- (this should probably be dragged over to rec.radio.shortwave, or rec.railroad 8)>>) The two systems i know of involve: Using wilfully leaky coax. An open weave braid allows noticeable amounts of signal out, and in. Some amplifiers and mixers and away you go... A system in NY City, allows the police to take their standard HT's into subway stations, while staying on the same channel. They found there was enough loss between topside and underground that they could equip each station with an above ground antenna, directional couplers, amplifiers, antenna(s) below ground. The loss "down the stairs" was enough to keep the underground transmitter from getting into the above ground receiver on the same frequency, and vice-versa... thanks dave pierson |The facts, as accurately as I can manage Digital Equipment Corporation |The opinions, my own... 600 Nickerson Rd Marlboro, Mass 01752 pierson@cimnet.enet.dec.com
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!umich!yale!cs.utexas.edu!uwm.edu!uakari.primate.wisc.edu!aplcen!haven!decuac!shlump.nac.dec.com!ryn.esg.dec.com!cimnet.dec.com!pierson From: pierson@cimnet.dec.com Newsgroups: sci.electronics,rec.ham-radio Subject: Re: naive question about RF propagation Message-ID: <799@ryn.esg.dec.com> Date: 17 Jan 90 02:03:36 GMT Sender: guest@ryn.esg.dec.com Followup-To: sci.electronics Organization: Digital Equipment Corporation Lines: 26