Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site redwood.UUCP
Path: utzoo!watmath!clyde!cbosgd!ihnp4!qantel!hplabs!hpda!fortune!redwood!rpw3
From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.physics
Subject: Re: Cancelling EM waves
Message-ID: <215@redwood.UUCP>
Date: Mon, 16-Sep-85 05:05:33 EDT
Article-I.D.: redwood.215
Posted: Mon Sep 16 05:05:33 1985
Date-Received: Thu, 19-Sep-85 07:25:17 EDT
References: <543@sri-arpa.ARPA>
Organization: [Consultant], Foster City, CA
Lines: 24

+---------------
| Let's say I have a device that emits an electromagnetic wave.  I put a
| certain amount of energy into it, and get most of that energy out ...
| Here's the question...  If I place [two of] them half a wavelength apart so
| that they are 180 degrees out of phase, the waves will cancel.  Now I appear
| to be getting no energy out of this system, at least not in the form of
| EM waves...  What is happening to the energy?... | Dan <DHowell@Xerox.ARPA>
+---------------

Sorry.

The waves only "cancel" on a line directly through the two devices. They
add to a lesser or greater degree at other, off-axis, angles. All you have
done is change the radiation pattern of the system, NOT the total energy
emitted. Radio stations do this all the time to control their directional
pattern so they don't (for example) waste kilowatts on open ocean...


Rob Warnock
Systems Architecture Consultant

UUCP:	{ihnp4,ucbvax!dual}!fortune!redwood!rpw3
DDD:	(415)572-2607
USPS:	510 Trinidad Lane, Foster City, CA  94404


Brought to you by Super Global Mega Corp .com