Background Data:Military Communication and TheRadio GameRandy H. KatzCS Division, EECS Dept.University of California, BerkeleySpring 2007Quick History:Electricity and Magnetism in the19th Century• Alessandro Volta (1745 - 1827)– Volt: the unit of electrical potential(“electromotive force”)– Metals are “movers” of electricity: arrangemetals in an electromotive series based on abilityto gain or lose positive charges by contact– Voltaic pile: dissimilar metals separated bymembranes moistened by acid -- the electricbatteryE&M History• Andre-Marie Ampere (1775 - 1836)– Amp: unit of electrical current ("velocity ofelectrical flow")– Demoed that magnetic effects between twocurrent carrying wires are the same as thosebetween a wire and magnet– Electrodynamics: mechanical forces betweencurrent-carrying conductors -- critical for thedesign of telegraph apparatus, telephonereceivers, and loud speakersE&M History• Georg Simon Ohm (1789 - 1854)– Ohm: the unit of electrical resistance– Ohm’s Law: I = V/R -- fundamentalrelationship between voltage (akaelectromotive force), current, andresistanceE&M History• Hans Christian Oersted (1777 -1851)– Forces of nature--light,electricity, magnetism, gravity--variations on one source. Magneticfield exists around a currentcarrying conductor. A deflectingforce, such as magnetism, wassomething completely new.Connection between electricityand magnetism. Demonstrated thiseffect with the deflection of amagnetic compass needle.E&M History• Michael Faraday (1791- 1867)– Farad: electrical unit ofcapacitance (storedelectrical charge).– Built on Oersted: Demoedelectric motor: wirecarrying current rotatedaround a fixed electro-magnet. Wire rotatesaround magnet. Alsoshowed how to makemagnet rotate around wire.Electrical Telegraph• Telegraph — “Writing at a distance”• Built on work of Volta, Faraday, Oersted.Signaling by means of electrical current along aconducting wire.• Basic idea: deflect a needle by connecting anddisconnecting a battery to a wire. Byalternating the connection between the + and -poles of the battery, the deflection could beenhanced: needle reverses its swing.Wheatstone and Cooke• 5 magnetic needles, deflected in pairs,selecting one of 20 letters of thealphabet. Original system required 5wires. Later reduced to 2 by usingcoding techniques. 20 km of lineinstalled along railway routes in 1838.Grows to 4000 miles by 1852.Samuel F. B. Morse• 1835: “printing telegraph” --key switches on current toelectromagnet. Pencil makesmark as long as key is helddown, drawing a long or shortline on a moving strip of paper.• 1837: Morse code – dots anddashes encode alphabet basedon frequency of occurrence inEnglish textJames Clerk Maxwell(1831-1879)• Maxwell's equationsdescribed fundamentalrelationship betweenelectricity, magnetism,wave propagation.Underlies all radio andcable communications.Light and radio waves arethe same phenomena.Provides theoreticalexplanation for why radiowaves can be focused andreflected just like light.Electromagnetic RadiationElectromagnetic Radiation• Heinrich Hertz (1857 -1894)– Hertz: unit of frequency:cycles per second.– Demoed experimentallywave character ofelectrical transmission inspace. Developed apparatusthat could transmit highfrequency, meter lengthwaves.Radio Communications• 1895: GuglielmoMarconi demoedelectromagneticradiation,created byspark gap, couldbe detectedlong distance.Radio Communications inWWI• Wireless plays key role!– Within hours of hostilities, British Navy cutGermany's overseas telegraphic cables;systematically attack German overseas radiostations and shut them down.– Germans similarly cut Britain's overland cables.… Marconi completes several radio stationsunder contract from the British government, toreestablish comms with overseas possessions.Techniques of communications intelligence(comint)—message interception, cryptoanalysis,direction finding, jamming, and intelligencegathering—developed rapidly.Airborne RadioCommunications in WW I• "It became clear as we made our preparations ... wasnot going to be anywhere near as simple as it hadsounded. The first problem was the shear weight ofthe wireless apparatus. The guts of the system was amarvelously archaic contraption called a spark-generator. This worked by creating an arch throughthe teeth of a brass cog-wheel spinning against anelectrode. Every time a tooth passed the electrode aspark jumped across the gap, and in this way, whenconnected to the aerial, it would produce a hideous,rasping crackle -- barbed wire made audible. Theprinciple of signaling was that the operator worked aMorse key to turn this excruciating noise into a signal:a crackle for a dash and a short one for a dot.”Airborne RadioCommunications in WW I• "That part of the wireless alone weighed about thirtykilograms. But there were all the other accoutrements thatwent with it. Power was provided by a dynamo fixed on to abracket under the aeroplane's nose and driven by a leatherbelt from a pulley-wheel on the propeller shaft: thatweighed about seven kilograms. Then there was the aerial:twenty meters of wire with a lead weight at one end to trailbehind us in flight, plus a cable reel to wind it in when not inuse: about ten kilograms' worth in all. Other accessoriescomprised a signal amplifier, a tuning coil, an emergencybattery, an ammeter, a set of signal rockets plus pistol anda repair kit. Altogether the wireless apparatus -- weighedabout 110 kilograms. Or to put it another way, the weight ofa very fat man as a third crew member."Portable Radio, circa WW IRadio CommunicationsWW II• Command and control in “lighteningwarfare” (blitzkrieg)– Mechanized warfare demands leading from thefront—radios in tanks let to quantitative edge– Rapid pace of operations does not allow forlaying of wires—by-pass hard points toinfiltrate behind the enemy• Combined arms coordination– Bring to bear infantry, tanks, artillery, airpower, even naval power– “Man” pack radios– Planes and ships don’t have wires“A Bridge Too Far”“A Bridge Too Far”“A Bridge Too Far”Insurgency Study• See Class Web Page:– http://www.cs.berkeley.edu/~randy/Courses/CS39K.S07/insurgentessayreq.html– Due: 8 March 2007The Radio Game• Two teams: Blue and Gold– Objective: be first team to collect thecomplete set of message segments and returnwith them to 320 Soda Hall• Messages spread around Soda Hall