interferencia fm

8/2/2019 Interferencia Fm

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Accession Number:ADB006029

Citation Status:Active

Citation Classification:

UnclassifiedField(s) & Group(s):

170401 - RADIO COUNTERMEASURES250200 - RADIO COMMUNICATIONS

Corporate Author:

ARMY COMMAND AND GENERAL STAFF COLL FORT LEAVENWORTH KSUnclassified Title:

FM Tactical Communications under Intentional Interference.Title Classification:

UnclassifiedDescriptive Note:

Final rept.,Personal Author(s):

Rood, Robert D.Report Date:

06 Jun 1975Media Count:

77 Page(s)Cost:

$9.60Report Number(s):

XA-USACGSCMonitor Acronym:

XAMonitor Series:

USACGSCReport Classification:

Unclassified

Supplementary Note:Master's thesis.

Distribution Statement:DISTRIBUTION STATEMENT A: Approved for Public Release;Distribution Unlimited

Descriptors:

*RADIO EQUIPMENT, *RADIOFREQUENCY INTERFERENCE, *RADIO JAMMING,MATHEMATICAL MODELS, COMPUTERIZED SIMULATION, LINE OF SIGHT,FREQUENCY MODULATION, SIGNAL TO NOISE RATIO, SOILS, RADIO RECEIVERS,MOISTURE, TACTICAL COMMUNICATIONS, RADIO TRANSMITTERS,RADIOFREQUENCY POWER, RADIO ANTIJAMMING

Identifiers:

AN/VRC-12

Abstract Classification:UnclassifiedDistribution Limitation(s):

01 - APPROVED FOR PUBLIC RELEASESource Serial:

FSource Code:

037260

Document Location: DTICChange Authority: 19991218 - Rep't was always unclassified. Distr scty cntrl st'mt 'A' in effect


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.1

'IJ,

. MASTER 0'1 MILIURYAllT AND SOIENOEfHlSIS unOVu, PAGE

N8llle of Candidate. 1 . : c . 9 b : ; e " r l . l t : - & : D ~ , ...R g , ; 0 ~ 0 " ' d : . _ _. '.r1t le of thesis N . ~ O.upi0!'lii""o.n;:,._ulQjP=:"'=.le-=1'....

/,. ,

.... "

. :

. . : ; ! i ~ ! G ~ ~ ~ _ . . , _ - - , Re arch Advisor' ,.L~ ~ ~ ' - ~ ~ ' U . ~ " :;;;; , Member, Graduate Research Facult1,i.-i?t


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19

oise a t t 2

F i ~ u r e 3. Phasor Diagrams for PM plus Noise.( a ) A ~ > r n ; (b)A6'


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j. , 20Sin q? ( t) , which also includes ~ n ( t ) and in turn is multipliedby the random variable l / rn ( t ) . This means the message ismutilated by noise and cannot be recovered. The resultingMthreshold effect" was graphically displayed in figure 1.

Equation 3b was approximated by assuming that (S/N)T T > 12dB. In this case the noisepresent would only be that due to background and internal reoeivernoise. The value 12dB has been determined to be a signa1-to-noiserat io whioh is reqUired by PM receivers to ensure negligiblemutilation of the desired signal at the output.21

I f a check by the computer program reveals that thereceived signal-to-noise ratio is appreciably less than 12dB evenWithout jamming, the program analysis will cease as we obviouslyhave designed a poor communications l ink.


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21PM CllTURE TEST RESULTS

In chapter two i t was mentioned that unclassifiedinterference tests had been conducted by the Army on i t s PMradios. 22 The results of these tests are particularly s i g n i f i c a n ~ ,in the development of this model as they offer actual equipmentperformance when sUbjected to co-channel interference by at ransmitter whose carr ier is modulated by audio noise. fhis isdirectly analogous to an enemy jammer employing the mosteffective form of Mspot M jamming against FM voice. By integratingthese laboratory tesUinto an accurate propagation model, theresul t will be a model Which will accurately predict theperformance of PM communications under noise jamming.

Figure 5 shows a plot of the performance of the AN/VRC-12radio set When subjected to interference from another AN/VRC-12radio Whose carr ier is modulated by audio noise. 23 The resultsare presented as a plot of the ar t iculat ion index versus thesignal-to-interference ratio in decibels. During the laboratorytests i t was assumed that "capture" by an interfering signalcould be considered to have occurred When the ratio of desiredsignal strength to interfering signal strength resultedin a,oDrresponding ar t iculat ion index (AI) less than or equal to0.7 measured at the output of the tes t l ink receiver. 24 Anexamination of figure 5 will reveal the just i f icat ion forsuch an assumption. I t can be seen that the ar t iculat ion indexdeteriorates rapidly With only a relat ively small drop inthe signal-to-interference ra t io . This i l lus tra tes that While to ta lcapture is a gradual process, i t s t i l l occurs relativelyrapidly once the signal-to-interference rat io drops below about


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232.5dB. This deteriorat ion continues unt i l S/I=OdB which i s ' ~ q ~ v a l e n t to the previously discussed predetection signal-to-noise ra t io(S/N)T when i t is equal to unity. At this point the communicationl ink can be considered to be worthless.

Before using the t es t resul ts in the computer modeli t is necessary to relate the signal-to-jammer (S/J) ra t io tosome measure of communication l ink quali ty more useful than theart iculat ion index (AI). Such a parameter i s the in te l l ig ib i l i ty(I) of the received signal . The relationship between the art iculat ionindex and in te l l ig ib i l i ty for the AN/VRC-12 radio se t is shownin figure 6. 25 By combining figures 5 and 6 one obtains theresul t shown ill figure 7 where the in te l l ig ib i l i ty i s plottedversus the sigl1al-to-interference ra t io . The extremes of usefulin te l l ig ib i l i ty extend from 40% upward. Any communication l inkwith a SII such that I i s less than 40% can be conl!lidered inoperable.For in te l l ig ib i l i ty levels higher than th i s , the l ink is consideredto be operable, but the message transmission time is increasedto allow for the repet i t ion necessary to raise in te l l ig ib i l i tyto a sat isfactory leveL In te l l ig ib i l i ty of 90% or greater canbe treated as original message length while as I of 40% wouldrequire repeti t ion of the transmission 4 or 5 times to ensure correctreception of the meSBage.26

In an attempt to make the scoring of the communicationl ink ' s quali ty more meaningful to the t ac t ica l commander andthe equipment operator-, the in te l l ig ib i l i ty scale has beendivided into a 5 interval scale. The 5 intervals were selectedon a purely rat ional basis . Their designations and the relatedapproximate message repeti t ions reqUired to insure message


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- - - - - - -,'1o,l!

"" 07....

'- ':>} - 0."H...Jhl 0.51!2>-'0 0.4 - - - - - -t-' ..J.J(!..iI - 03'2rl 0.1

0.1

O ~ - : : - ' ~ ~ ' : - - - = - , ' ; ; - - = - ' ' - ; - - = - ' , = - - : - , - . - - : - ' = - - - 7 ' : : - - = - ' = - - ; - ' : : - - - ' - - - - ' - - - ' o O.t 0.'- 0.3 0.4 0.5 o.c;, 0:1 O.li' 09 \.0to P. n:cul ,Al ' J:OIIJ -:r..,Of,')( (A"t)

1


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- - - - - -- - -

25

Intell igl .bil i ty( I ~ ) _1.0

A ----_. __ .- _.__ .... _ - - - - ~ ~ - _ . - - - -_.- - -----_. 0.9 (A) EXCELLENT COMMUNICATIONS

B (B) GOOD ..o.8 - (C) FAIR to(D) POOR to(E) UNSUITABLE"0.7 C0.6 -

D.50.40.3 E I I

I I0.2 I II i

0.1 I II I

I l0-1 0 1 2 3 4 5 6 7 8 9

Signal-to-Interfprence Ratlo(S/I) in dBFigure 7. I versus sIr for AN/VRC-12 versus AN/VRC-12


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26reception (.we as follows,27Excellent 1Good 1 - 1tFair 1! - 2tPoor 2! - 4,Unsuitable greater than 4tThese intervals wil l be employed in the computer

model to i n f o ~ n the user of the quali ty of the proposedcommunication l ink once the related signal-to-inter1'erence rat ioa t the receive:r has been calculated .


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Ch&pteZ! IVMODEL DEVEI.O?MENT

In chapter three the relationship between the receivedsignal and in te l l ig ib i l i ty was developed. I t is now necessaryto develop the relationships for the remainder of the systemi l lus trated previously in figure 2. The most cr i t ica l componentof the actual communication l ink are the equations for signalloss over different types of terrain. In this chapter variousequations will be developed to express propagation losses forvarious terrain configurations. These equations will then be integratedinto the entire system so a value for the friendly signaland jamming signal a t the receiver can be calculated.

VHF C O ~ ~ U N I C A T I O N S Very High Frequencies (VHF) cover the frequency

range from 30 to 300 MHz. The portion of th is band that we willbe concerned With for mili tary FM communications is limited tothe 30 to 80 MHz range. For this range we wil l be concerned onlyWith ground-wave propagation as VHF waves are not reflectedfrom the ionosphere.

The ground wave is made up of two components, asur'.ce wave that follows the contours of the earth anda space Wave that moves through the atmosphere either d i r e c t l ~

27


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28~ reflection from the ground obstacles, or by refraction anddiffraction occuring within a few miles of the earth's surface. 28For radio frequencies above approximately 20 MHz, the surfaceWave portion of the ground wave attenuates rapidly, becoming neg11g1ble

, a few hundred feet for a frequency of 30 MHz. Successful"ransmission therefore depends on a propagation of the space wavebetween the transmitting and receiving antennas. I t is thisspace wave that is so greatly attenuated by obstacles, eithernatural or manaa4e.

COMMUNICA.TION LINKSThe signal power, S, at the received end of a

communication l ink will be considerably affected by propagationconditions and the uncertainties introduced by n a t ~ r a l andhuman elements in the operation of the l ink. The exact form ofthe signal power equation can be assumed to obey the equat1on: 29

S (dB) = P + GIl + G12 - L (d) (I )Where P = transmitter power in decibels

GIl , G12 = the transmitter and receiver antenna gainsin db, respectively

L = the signal path lOBS in db which is primarily afunction of the path length, d, in kms.

In general, a ll these parameters may be variable. Propagationconditions will always introduce uncertainties in L, and theantenna gain factors Gl l , G12' and P are a funetion of the antennaconfigurations and t ransmitter power output respectively.


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29The decibel (db) is the preferred unit for expressingpower'ln communication analysis because i t is logarthmic.fwo values can be multiplied or divided by adding or sUbtractingtheir logarithms. Since amplification and attenuation aremultiplication and division processes, the decibel proVidesa handy means of expressing changes of power by simpleaddition and SUbtraction.

For example, i f a signal is transmitted a t a certainpower and is received at 1/1.000 ; 10-3 that power, i t hassuffered a }O dB loss ( ; 10 10g10 10-}). I f this reducedsignal is transmitted again and undergoes similar attenuation,the final signal is 1/1,000,000 =10-6 i t s original strength(1/1,000 1/1.000). I t is simpler to add 30 dB and 30 dB toget 60 dB as the to ta l attenuation of the signal .

I t is inevitable that the signal expressed in equation1 will deteriorate during the process of transmission andreception as a resul t of some distortion in the system suchas jamming or because of the introduction of noise, Which isunwanted energy, usually of a random Character, present in atransmission, due to any cause. Since noise will be receivedtogether with the signal. i t obViously places a l imitationon the transmission system as a Whole; in a severe case, i tmay mask a given signal to such as extent that the signalbecomes unintelligible and therefore useless. The signal-tonoise ratio (S/N) expresses the ratio, in decibels, of signalpower to to ta l noise power in a channel and is consequentlyan indicator of received signal quality. In chapter 3 i t wasstated that high quality PM volce communlcations are assumed


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30to requlre a slgnal-to-nolse ratl0 of about 12 dB. I t lstherefore lmportant that some means of calculatlng backgroundnoise be introduced.

The nolse present a t a receiver when no intentions'interference ls present is a function of environmental noiseand internal receiver noise. The equatlons for computing thesenoise values are as follows:30

Nr =ktoBrFr =internal receiver noiseNa =ktoBrFa =environmental nolse (2)N =Na + Nr =equlvalent recelver input noise

Where Fr = receiver noise figure (= 15 dB for mobtle vehicularVHF)

Fa = environmental noise figure (= 20 dB for CentralEurope suburban noise)

k =Boltzman's constant =1.38 X10-23 JOUles/oKto =reference temperature = 2 9 0 ~ Br = recelver banswldth (= 32 KHz for military PM).Making the computations indicated in equations 2

reveals an equlvalent recelver input nolse for Central Europeof -128dB. Consequently, the computer model wll1 check eachcommunlcations l lnk before jamming to ensure the receivedsignal at the receiver input is a leas t -116 dB (= 12 dB 128 dB). This wl1l ensure that an operational communicationsl ink is being analyzed. The abil i ty to make thls check wtllalso give the model the abil i ty to plan the coverage of FM volcecommunlcations When no jamming ls present.

Durlng the jamming analysis, the eqUivalent receiverinput noise (N) 1s neglected as N 1s seldom as large as the


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31Jamming signal (J) . The model computer program will use theS/J ratio with the data from figure 7 to determine the qualityof the communications l ink . I f N was appreciable compared toeither J or S, then the S/J ratio should be modified to aS/(J+N) ra t io .

:PROPAGATION LOSSPree Space Path LOBS

A free space transmission path i s a straight - l inepath i an ideal atmosphere. As no interferenoe or obstaclesare present, the relationship between transmitted and receivedpower may simply be stated as: 31

:l. ':P r =...5:t..ir X 2 l ' t(4 ' tTd1where Pr =received power in watts

Pt = transmitted power in wattsgt and gr = the respective direotivi ty gains (interms of power ratios) of the transmit and receiveantennas With respect to an antenna radiatinguniformily in a l l directionsA = the wavelength in kmd = the separation between antennas in km.

By substi tuting the relationship between wavelengthand frequency ( A =300/f(MHz)) into equation 3 and simplify-ing the results we obtain the relationship a

~ (41.87 df)2 :Pr Stgr

The expression for free space path 108s is then:L =20 log,0 (41.87 df) (5)


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32where f is the frequency in MHz.Equation 5 will be used in the model to determine

path 1088 when either the friendly transmitter or Jammer areairborne and the receiver is on the ground.Plane Earth Path Loss

The theoretical received power for transmission overplane earth i s given approximately by the relationship:32

Pr =gtgr Pt (6)where Pr , Pt , gt, gr and d are as defined for equation 3.

ht, hr = the transmit and receive antenna heights inkilometers.

The expression for plane earth path loss can then be oomputedfrom the formula

L =20 log10 d2/hthr (7)The equation given above is limited to transmission

over water and f la t , barren land. In addition i t is independentof the particular frequency of operation. A form of thisequation has been adapted by Egli in his work to predict lossesfor mobile communications when l i t t l e is known about specificterrain obstacles and an estimate of area coverage of a radiosisnal is required. 33 Unfortunately. oomparisons with actualterrain losses showed eqn. 7 to be unduly pessimistic in i t spredictions. The actual comparisons between predicted and mea-sured losses will be given in chapter 6.

A more accurate equation for field strength calculationjover smooth ground takes into oonsideration the moisture contentof the soil n . the antennas. For a smooth ground path. the


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33influence of the ground oonstants on field strength isdetermined by the value of the effective dielectric constant(c > whioh 1s determined mainly by the water content of theground.34

For vertically polarized VHF ground wave propagationat low heights, the equation for the total received fieldstrength as a fUnction of ground moisture iSl 35

J30P,. i r c l 1T (:-I:j e " :J " "In order to calculate an expression for path loss

from this expression i t is f i r s t necessary to determine thepower (Pr > at the input to the receiver. Consequently, arelation is needed between the field intensity at the receiversantenna and th t power into the reoeiver. The Poynting relationbetween the 1'1eld intensity Er and power Pr 18

J2r = 480 't t 2 Pr (9)Sr ~ Where Er is in volts per meter, Pr i8 in watts.36 B.Y oomUningequation 8 and 9 the expression for path loss over smoothearth is derivedlL = - 1 0 1 0 g l O [ t U ~ ~ O ~ ~ ) ~ ( 1 " ' ~ ' 3 ( t J . ) ~ f : l . ) ( i + ~ 3 1 ( ~ } ) h ; fJ,)J (10)Where f = relative dieleotric oonstant

f = frequenoy in MHzd =separation between antennas in kmht, hr =transmit and reoeive antenna heights in km.

The values for the relative dieleotric constant forground conditions in oentral Germany have been found to varyfrom 4 for very dry earth to 30 for wet ground With a medianvalue of 13.37 This range of values along with equation 10


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34will be used in the model to calculate propagation lossesfor flat earth communication' l inks.Obstacle Fath Loss

Egli 's s ta t is t ica l approach38 for determining propagation loss is appropriate for situations in Which the actualterrain is unknown and an aKWags' terrain must be assumed.However, in my analysis the profiles are known Or may beextracted from a map analysis. Therefore, propagation lossesmay be estimated for the particular terrain in the communicationpath. Obviously, the equations previously introduced forair-to-ground and l ine-of-sight (LOS) communications are notsufficient to cover a ll possible terrain conditions that couldoccur. Two additional terrain categories are shown in figure8, the single-obstacle path (SOP) and the multiple-obstaclepath (MOP). The single-obstacle path is a terrain obstacleso situated that a LOS path exists from a single obstacle toeach terminal, as shown in figure 8a. In the case of a multipleobstacle path, more than one terrain obstacle exists such thatno LOS path exists from any single obstacles to both terminals,as shown in figure 8b.

The basic general equation to compute propagationlosses for these terrain profiles is 39L =Cl+Ft(H!d)+F2(W!d)2+02f+03l0gf+C4d+CSd2 (11)Where L =path loss (attenuation in dB)

d = to ta l path length, in kilometersH =maximum obstacle height in kilometers above a Jine


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35

Figure 8. Propagation Paths. (a)SOP; (b)MOP

I~ (a)

________ ~ d I(b)


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36joining the path terminalsf = operating frequency in megacycles per second.

The C's are constants and the pIS indicate functions. The speci f ic equations for the non - LOS paths are:SOP:L =46.2 + 1070 (H/d) - 7500 (H/d)2 + 0.00268 (l) + 2 8 . 3 4 ~

log (f) + 0.879 (d) - 0.00378 (d)2 (12)MOP:

L =119.9 + 287 (H/d) - 11000 (H/d)2 + 0.00425 (l) +14.98 log(f) + 0.541 (d) - O.00159d2 (13)

Equations 12 and 13 are for obstructed paths Whenrelatively ideal local-s i te conditions exist at both pathterminals. Such conditions eXist When transmitting andreceiving antennas are clear of a ll obstructions in the immediate si te areas. These equations will be used in the model forany communication l ink where one or more obstacles exist .

Profiles representing terrain configuration paths forWest German terrain were drawn and classified according toWhether the paths were LOS, SOP, or MOp.40 In a sample of 128profiles, 27 were LOS, 53 SOP and 48 MOP. For a somewhatlarger sample, i t was found that approximately one-third ofthe single-obstacle and mUltiple -obstacle paths had obstaclesbetween 20 and 40 meters high. Approximately one-third of themultiple-obstacle paths had obstacle 'heights greater than 60meters, while no single-obstacle paths were found to fa l l intothis category.


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37EQUIPMENT CONSIDERATIONSAntennas

In order to couple the output of a radio t ransmitterto space, i t is necessary in each case to use some type of.structure capable of radiating electromagnetic waves or receiving them, as the case may be. An antenna is such a structureand may be described as a metallic object, often a wire or acollection of Wires, used to convert high-frequency current intoelectromagnetic Waves which then travel and behave as describedby the equations in the preceding sections, and are f inallypicked up by the receiver antenna. Apart from their differentfunctions, transmitting and receiving antennas behave identical ly

Since a ll practical antennas concentrate their radiation in some direction, to a greater or lesser extent. thepower density in those directions is greater than i t wouldhave been had the antenna not concentrated i ts radiation 1nthis manner. Accordingly. antennas may be said to have gain.The term most frequently used with respect to an antenna's gainis Mdirective gainM

Directive gain, in a particular direction, is therat io of the power density radiated in that direction by theantenna to the power density that would be radiated by anisotropic antenna.41 An isotropic antenna is an antenna thatcannot eXist in practice, but since i ts radiation pattern isperfectly omni-directional, or spherical. i t s properties arevsry easy to visualize, calculate, and use for reference. Tocompare the antenna to be tested with an isotropic a n t e n n ~ ,


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38both power densi t ies are measured a t the same distance, andboth antennas must be assumed to radiate the same to ta l power.

While direct ive gain refers to any part icular direct ion.the direction of the maximum direct ive gain i s usually thatwhich concerns us most. The correct name for maximum direct ivegain is direct ivi ty and refers to the gain in the directionof the major lobe of the radiation pat tern . 42

The importance of antenna gain to communicationl inks i s that it increases the effective power of a transmissionjust as surely as does amplifier gain. A dis tant observerlocated along the main beam would receive as much signal powerfrom an antenna with a gain of 30 dB, radiating 1 watt , as hewould from an isotropic radia tor a t the same distance with anoutput of 1,000 watts. The effectiveness of the transmissioni s similarly increased by the gain of the receiving antenna,This abi l i ty of a direct ional antenna to increase theeffectiveness of transmission i s not only important for theimprovement of communications but can also be used to decreasethe effectiveness of an enemy jammer, I f the major lobe ofa receiving antenna i s pointed away from the jammer anddirect ly toward the friendly t ransmit ter, the desired signalwil l be greatly enhanced while the jamming signal i s degraded.

The omnidirectional whip antenna presently used by theArmy with i t s mobile FM radios i s essential ly a center-fedhalf-wavelength antenna and therefore has a directive gainof 1.64 or 2.15 dB broadside to the radiator . While th isomnidirectional antenna makes mobile communications simp] c,',it also makes the receiver susceptible to jamming. Fortunately,


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39the army i8 presently developing a directional antenna whichwill enhance oommunications while reducing Busceptibility tointerference. This antenna is a broadband log-periodicdesigned to cover the range from 30 to 80 MHz without therequirement to change elements while s t i l l being portableenough for tac t ical use.43 The radiat ion pattern for thisantenna in comparison with that of an isotropic antenna isshown in figure 9. The main beam offers a gain of 6 dB aboveisotropic, while the antennae backlobe in 8 dB below isotropic.A jammer or transmitter located broadside to such an antennawould be subjected to an antenna gain of only about 2 dB. Thesewill be the three categories of receiver gain used in thec o m p u t e ~ model when computing the jammer to receiver l ink .Since the enemy's jammers will normally be operating from hisside of the FEBA, the jammer signal will usually be SUbjectedto a -8 dB gain at the receiver, While the friendly signalwill receive the benefit of the major lobes 6 IB gain.

I t can be assumed that the jammer antenna Will eitherbe a half-wave whip or a directional log-periodic antenna.While there are antennas With greater gain, the log-periodicoffers the f leXibil i ty of being relat ively frequencyindependent While s t i l l providing significant directive gain.Therefore, the values of jammer antenna gain suggested in themodel will vary from approximately 2 to 8 dB, depending onthe antenna conflguratlon. 44Transmitters

The t ransmitter assumed to be used in this analysis


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40

.-._--.... ------ ,- - " - " ~/ ' /( -...."/ ' ....

/ "/ \I

f \

II, , J IsotropicJ Antenna, /

/....

Figure 9. Field Strength Radiation Pattern forVHF Log-periodic Antenna


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41is the one used in the army's mobile configuration of theAN/VRC-12 radio. The basic receiver-transmitter is theRT-524 which has a rated output of 35 watts for high powerand approximately 2 watts for low power.45While exact jammer transmitter charactertics arediff icul t to predict in advance, we can assume that theenemy will use noise modulation against FM voice and that "typical FM jammer transmitter power outputs will fa l l anywhere from 500 to 2,000 watts.46


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Chapter VMODEL COMPUTERIZATION

In the preceding chapters the parameters of theproblem and the just i f icat ion for their development waspresented. To fac i l i ta te their use in a real-time analysisand to reduce the tedious mathematics involved, i t is advisableto computerize the model.

FLOW CHART

The f i r s t step in developing a computer program i sthe development of a flow chart so as to graphically i l lus tra tethe interrelat ion of the problem's parameters. The flow chartfor this problem is shown in figure 10. Note that the pathloes sUbroutine (figure 11) is used tWice during the run ofthe problem. The f i r s t use of this subroutine is in thecalculation of the desired signal at the receiver input. Thissame subroutine is then used to calculate the level of thejamming signal a t the receiver input.

COMPUTER PROGRAM

The complete computer program which implements theflow chart shown in figure 10 is shown in figure 12. Examplesof different computer runs are presented in the appendix fordifferent terrain and equipment configurations.42


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S

F1gure,10. Flow Chart

r-- FI

XMTR. TO RCVR.DISTANCE

L-_--...=----J XMTR. POWER

COMPUTE THE XMTR.-RCVR.~ _ PATH LOSSS

RCVR. ANT. GAIN

FREQUENCY

COMPUTE THE SIGNALAT THE RCVR. INPUT

COMPUTE THE SIGNALTO-NOISE RATIO ATTHE RCVR.

A

J

JAMMER ANT.GAINJAMMER TOROn. DISTANOEJAMMER POWERJAMMER LOa.RELATIVE TOXMTR .liRCVR.LINK

COMPUTE JAMMERRCVR. PATHLOSS

1COMPUTE JAMMERJSIGNAL AT THEL...._-.-__ ROVR. INPUT-'1

I COMPUTE THE

I

OOMMO.QUALITYi~ _ t _ .C END )

SIGNAL-TOJAMMER RATIOCOMPUTE THERECEIVED SIGNALINTELLIGIBILITYPRINT THEQUALITY OF THEDETECTED SIGNAL

C


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ABN ~ _ ---41 ' - ~ - F S _ - i COMPUTE FREE-XM T y ..-.---- . ! SPACE PATH LOSS.. ,_]_J

/ G/ PATH M O R ~~ T A C L 1 i ' ~ - - - . . : > f - . . . . THAN ON

)// ST E

- _ . - ~

r- _.- - - : LpE ,I ~ O 'I - ~ : p __]__ ICOMPUT PLANE- COMPUT SINGLE 1m1IIn:>T1"'m


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45Figure 12. Tact ical FM Jamming Programu l PPI; \ 'T"TACnU,L n , JM'W,ING A ~ I ! \ L , ( S I S 1'"liGkAC","U2 r - ' r ~ I N T " II(' 3 I ' i,,"38 PRINT"--------------------------------------"39 PhINT rr It40 GOSUfJ 50043 LE T Ll =Li l iJ PldNT"XMTk/RCVf< PATH LOSS IN DB IS="L lL ~ PhI NT"-" .. - _f f46 LET PI =lLJ*LGl ()50 LET 51=P I+Gl+G2-LI51 PRINT""ECEIIiED SIGNAL ',vITHOUT JAMMING IN lJb="SI55 LE T G2=SI+12e56 PRINT"r


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1,5U ii - ~ < 1 < ' : - 1 . : { 1;:;";\ ' : . j l , 46J 3 I S 3 < = 2 . ~ ' IHEN ~ ~ L,OS l ' i \ INI "Ui'iUSAl.'Lf:: C01':I":I::. LlJ'I ' ,"/ ~ I O GG TO 1,90415 I 'F, INT"EXCELLENT C l J i " ~ I ( J . " L l i ~ O GO TO /J90425 PRINT "Pb0R C0t1ML)."./130 Ge T0 1190435 PhIN'j t lFAlk C C : ~ ~ l - , C . t l 1:"0 GG T0 1,90/ ILIS fJ hll\1T nGOCD C0f\jI'iO."1150 GC 'Il; ",10"55 p" I tn "U , \ jSUITA"LE CGt'iMO. LINt< " ~ V E N '"ITHOUT J.['i',('ilt"G"1,60 GO T D '1901 1 6 ~ ~ I-'l-


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47The instructions to the user in the computer print

out are designed as typical values for equipment presentlyin the field. Future developments in hardware operating inthe VHF range (30-300 MHz) can be easily adapted for use withthis program as long as the signal-to-interference performanceof the receiver is known.


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Chapter VIEVALUATION OF RESULTS

To determine the validity ot this computer programi t is necessary to compare the predicted values with actualfield tes ts . As the performance of the receiver was basedupon actual laboratory tests When sUbjected to various signalto-interference rat ios , the only portion of the model Whichrequires analysis are the equations used to calculatepropagation losses.

PREDICTED VERSUS MEASURED

As previously mentioned in chapter 2, the most usefulf ield tests of VHF propagation losses were performed in 1967by the Inst i tute for Environmental Research.47 These testsare particularly useful for the purposes of tes t ing this modelbecause terrain profiles were drawn for each of the measuredcommunication l inks. Figures 13.a. and 13.b. show the resul tsof tests for several l ine-of-sight paths for different frequenciesand distances. I t should be understood that each propagationpath had varying amounts of vegetation and bUildings, even thoughthere were no actual terrain obstacles in the LOS paths. Inaddition, the tes t measurements were SUbjected to a :3 dB errordue to faulty antenna gain measurements. Two measurements weretaken at each tes t s i te . An in i t ia l measurement was followed

48


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Transmissionloss(dB)90r "'- E=13"'-. ' t=30 Flat Earth Model---------~ ~ ' J ~ 4 "' Smooth Gnd. Model- - - - - "' (good g n d . ~ = 3 0 ; m e d l u m gnd.(:=13;""'- "'- poor g n d . ~ = 4 ) 100 L Test Result S Average C J "'II I "'I110

120

130

140

150

0 " "

"'"'- """' "c:::J:--... "" ""' "-"'Frequency: 20Mhz 0

..,Antenna Heights: '"mtr; 3.3m "-Rcvrs 1.3m 0. "'

_ :--...

160 '-------!12:;-----l;b.--+.... - - " l : ; - - ' ' r - ~ . _ _ _ i . l - I _ ' ' ~ I _ ; : ; _ - _ _ _ ; c ' ; ; 1 _--;:::!;-__,. .. - 3 4 5 6 7 8 9 10 l"S 20Distance in KmFigure 13.(a) Comparison of Line-of-Sight Losses(predicted)with Data derived from Measurements{field tests)


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50Transmissonloss(dB)90 r, "- ""- Flat Earth Model - - - - - 1 0 0 ~ ' : ~ : ~ = 1 ~ = Smooth Gnd. Model - - - (good g n d . ~ = 3 0 ; m e d i u m gnd.(=13;

"- "- poor gnd .1:.=4 )" "- "- Test Result 's Average c:J"110 -. ",

"'""- "-

","- '" "

Frequency: 50Mhz30Antenna Heights:Xmtrs 4.OmRcvr: 1.7m

140

150

160 I - -L __ _ + _ I - - - - I - ~ ' _ . L - ~ I _ L _ " _ l ------ ' - -1 _1 2 3 4 5 6 7 8 9 10 15 20Distance in KmFigure 13.(b) Comparison of Line-of-Sight Losses(predicted)with Data derived from Measurements(field tests)


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51by a measurement from the optimum location found within 100meters of the f i r s t .

Figure 13 compares these measured propalation losseswith a modified version of Egli 's equation (eqh. 7. chapter 4)denoted as the f la t earth model and with equation 10 (chapter 4)referred to as the smooth ground model. In an attempt to makeEgli 's equation f i t the data, the predicted loss was reducedby 17.7 dB. This modification was fair ly successful for afrequency of 50 MHz, but failed to adapt to a frequency changesuch as i l lustrated for 20 MHz. However. the smooth groundmodel covers the range of tes t results fair ly well within i t srange of variation for different dielectric constants,particularly for the lower frequency of 20 MHz. Therefore. thesmooth ground model was chosen to be used for l ine-of-s ightcommunication l inks.

Figure 14 compares the results of the single-obstacleand multiple-obstacle propagation equations with actual f ieldtes t results . The tes t si te variations are due to differentmeasurements taken a t the same si te a l l Within a 100 meterradiUS of the original one. When the measurement errors previously discussed are taken into consideration, the comparisonproves to be qUite good and consequently justif ies the useof these equations in the model.

CONCLUSIONSThe specific question Which this stUdy has attempted

to answer is - - is i t possible to develop a computerizedmathematical model for PM tac t ical radios operating under the


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52

_.

SINGLE-OBSTACLEPROPAGATIONMODEL

MULTIPLE-OBSTACLEPROPAGATIONMODEL

DISTANCE(Km) 5 10 20 20 30 30 30 50OBSTACLE .08 .10003 .03 .07 .05 .130 .07HEIGHT(Km) _.-TEST SITE 160. 1 165.1 167 . 172.Sto127 . 127 . ' 135. 138.to to to to to to to)122ARIATIONS (dl t 61 . 1 2 2 . ~ 131 133.1 158. 165 164.7

124.( 126.1 1 3 4 . ~REDICTED 1 3 4 . ~ 160.1 161 . 161 .Ii 169LOSS (dB)

Figure t4 . Oomparison of Field Test Results withPredicted Propagation Path Losses for SOP and MOP


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53influence of enemy jamming so as to optimize communicationsfor particular battlefield terrain and various equipmentconfigurations?

The answer 1s yes, 1t is possible. Oomparisons of thepropagation portion of the model with actual field tests haveshown the results to be an accurate indication of "real-world"conditions while the integration of actual equipment performanceunder CO-Channel interference adds a realism to the model whichenhances i ts usefulness as a training or planning device.

By inserting the characteristics of actual PMcommunications equipment and the terrain over which i t isexpected to operate. the user will receive as an output notonly the vulnerability of a particular communication link tojamming. but also an indication of what steps should betaken to reduce the effectiveness of enemy jamming.


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54

APPENDIX

COMPUTER RUN EXAMPLES

Figure 15 i l lustrates the output of the computerizedmodel for varying battlefield configurations. For ....p l ' ,figure 15.a. is a l ink where the received signal-to-noise ratiois inadequate even Without jamming. The remainder of theexamples i l lustrate l inks Which produoe varying signal-tojamming ratios and consequently a varying quality of receivedsignal. These l inks are respectively an unusable, fair andan excellent commUnication l ink.


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55INPUI Xi'l H< (,NT. G f ; P l ; < ~ . j : : > i'U/\ vJHlJ',6 I 'Ok OIHt:CTI0NflL'!

INPUT kCV/i ~ N T . GAIN ;2.1::> .Uk WHIr,6 FON D I H ~ C T I 0 N A L '!6

INPUT I'!tEO. IN MHL?:, 0INPUT XMTk TO kCVk D I ~ T A N C E IN KM "?30INPUT XM"lk PWk. 0UTPUT IN ~ A T l S I 2 . 0 F0R LUW POW EN,3 VOR HIGH PWk.73:'-'

INPUT HCVh A i ~ ' j . HT. I, . K i 7 . 01THE F0LL0WING IS A CALCULAlI0N 01' XMTH TO keVk FAlH LOSSINPUT XMn;\JA1'lMEk ANT. HT. IN KM7.01

IF 'iHt. J . \ t j T j ' . ' J / ~ I ' j l l ~ h l ~ A b r ~ . , I L ' ~ t - ' L J l , 1; IV f..\ I ' L ( ; i t:../::"j(irl l , ; l . h / h ~ ; ~ . PATH, INPU1 !l, 21 IF" A SINGU::-Ol-1:::'1{;CLE F'ATH, INPUT A 3.IF A 1 " 1 U L T I I U : - 0 H ~ ; l ( ; 1 . t PATH.INPUT A 4?4INPUT MAX. ObSTACLE Hl. IN KM A B 0 V ~ A LINE JOININGTHE PATH TERMINALS7. 120;,;,-:1 h/iiC VI< I-'fdH LOSS IN IJD 1S" 161 . 3 3 "kEl :d V,_O 51Gi,AL \oil TH0UT J M 1 > ' ~ I N ( ' I , OB=-133.KSi3RECEIVED SIGNAL-18-NOISE HATIO IN DU=-S.B9339

0 1 ~ S U I 1 AbLE (;OIIMO. LINK FVt:N \1/11HUUT JNI,I ',I.\J(;)II' YOU W I ~ H 1"0 E X E C U 1 ~ ANUIHEk PROBLEM, INPUT A 'I-." ?7

- - - " - - - - - - - ~ - - - - - - " - - - - - " - "

Figure 15. Sample Computer Runs.(a)Unsuitable Commo. Link

iT i IX, liSt 5 s. r ' , ; o . " : { " ' - . ~ ' _ . 4 .... ......_ . . , . _ - - - - - ~ ~ ......... ...... --" .. ....


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Figure 15.(b) Unusable Commo. L1nk 56INI'UI XWlh i I f ~ j . liA!t'JI , ~ 1:J r ( ' J l ~ vJH1I-' (, r U I I J I I ~ U ; ' I I UNfll.'/

(,

INPUT RCVk ANT. GAIN 12. 1:J F O I ~ ~ H I P . 6 fOR DIRECTIONAL16INPUT FRED. IN MHZ'150INPUT XMTk T0 RCVH D I ~ I A N C E IN KM120INPUT XMTR PWII. OUTPUT IN WATTSI2.Q FOR LOW POWER.35 ~ 0 HIGH rWR.135INPUT ReVR ANT. HT. IN KM'1.01THE f 0 L L O W I N ~ IS A CALCULATI0N OF XMTk TO kCVR PATH LOSS- - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - - - - - - - -INPUT XMTk'JAMMER ANT. HT. IN KM7.01IF THE XMTR'JAMMER IS ABN INPUT A l l IF A FLAT EARTH COMMO.PATH. INPUT A 21Ir A SINGLE-UbSTACLE PAIH.INPUl A 3.IF' A i ~ U L T I P L E - 0 8 S T C L E PATH. INPUT A 4'13

INPUT GBSTACLE HT. IN KM ABOVE A LINE JOINING THE PATH1 ERMI NAL.S1 .08

XMTH/IIGVII PATH L.OSS IN DB IS= 134.711RECEIVED SIGNAL WITHOUT JAMMING IN 08=-107.27

HECEI VED SIGNAL -HI -N iJ l SE kAT! 0 IN DB= 20.7299INPUT JAMMEr, ANT. GAINJUSE A VALUE Fk6M 2 Hl 8?2INPUT JAMMER 10 RCVR UISIANCE IN KM'120INPUT JAMMER PWR. IN v:A1TSJUSE A VALUt: IN THER A N G ~ fROM 530 TO 200012000I i ~ l i j T RELATIVE J A M M U ~ L.0CAlIONJ IF P. lJll(r:CTlO,'Jr,L ANT. IS I ) ~ ; F I ) U ~ r : b fOR A J A I ~ ; ~ E H 0ETWEEN THE RCVk/XMTR LINK.? fOR AJAMMER R k O A D ~ I D E TO THE LINK. AND -8 FOR THE JAMMER 10 THE'lEAR Of THE XMTI'. IF A WHIP RCVR ANT. IS USED.ENTER 2 . 1 ~ 7-8THE f 6 L L O ~ I N G IS A CALCULATION Or JAMMER 10 RCVR I'AIH L U S ~


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INPUT O H ~ T A C L E HT. IN KM. Ab0VE A L I N ~ J0INING THE l'ATH 57'I c_ h," I l AI.. ?07

JAMME:IUI\CVf\ PATH 1..0:;S IN IJH IS= l;jil.P(1


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F i ~ r e 1 IclFair Commo. L1hk 58TAC1ICAC-FM J A A ~ r N G A N A L Y S l S ~ k O G i I A M ;1'WlI1 fYI/;, {\NT. G f . \ l i ' J ; 2 . \ ~ ~ C , H \,;HII-'.6 FOH llJi


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------------------------------------- 591''l:I'IiT X i ~ T f ( \ J A { ' I , H f : ; . ; ANT. HT. IN ,v,7. 01

IF ' THE X r ' , T I \ \ J I \ ; - ' l r ' , h ~ IS AflN"INI ' I iT A lJU A FLAT EMnH COMo'C.PATH, li\WIIT A ~ " IF" A ,SINGLE-Ci':iSTI\CU, Pi'Th. INPUT A 3;IF A MULl IPLE-08STCLE P A T H . I ~ P U T A 4?3 INI'IIT Of3STACLE HT. IN KM PIi.l0VE A LINE JC:J1


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60NPUT XMlk ANT. G A I I ~ 1 2 . 1 ~ F0h WHIF ,6 f 0 1 ~ D I R ~ G T I 0 N A L 16 F1gure 15.(d) Exoellent Oommo. LinkINPUT HCV1-: ANT. G A I i ~ I ( ! . ( ~ HJ j , v;HIh6 Hi" LJIl


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FOOTNOTES

1. David L. Woods, A History of Tactical Communications.(Orlando Florida: Martin 00, 1965), pp. 57.2. John M. Oarroll, Secrets ~ Electronic Espionage.(New York: E.P. Dutton, 1966), pp. 4 -46.3. MG Stewart C. Meyer, ".&Me Started the New Year withRenewed Emphasis on Electronic Warfare," Army EW, ( M a r c h / ~ p r i l 1974), pp. 27-30.4. Ibid.5. Henry Magnuski, IlJamming of Communication Systems

Using FM, AM and SSB Modulation," lRi Transaction on MilitaryElectronics, MIL-5, (January 1961), p . 8.6. J . Ross Heverly, Range, Mobility and TransmissionRelia i l i t Factors for Division Commu ications, Dept. of theArmyt Army esearch ice echo Memo. O}-'l-408, June1962}, pp. 51.S2.7. John J . Egll, "Radio Propagation Above 4OMO overIrregular Terrain," Proceedings of the I .R.E., (October 1957),p . 1387.8. of the Army, TM 11-486-6. ElectricalOommunicat En ineerin Radio, (Washington:Government ice, AUgUst 6), p. 9-2.9. Ibid.

10. John J . Egl1, "Radio Propagation Above 40MC overIrregular Terrain," Proceeding of the IRE, (October 1957),pp. 1383-1391.nt rference Pred

n ,Pro , Jan.

13. M.E. Johnson. Tabulations VHF Propgatlon Data~ O , . : : b : : t : i ! : a ~ i ~ n : : e ~ d : : : - : : o v = e - : : r ~ I ~ r ~ r . . l i : e ~ U ~ l ~ a ~ r ~ T ~ e ~ r ~ r ~ a : i ; n ~ ~ a ~ t : ~ ~ ; ~ : ~ o ~ a - n " ' d . = . r i ' ; : o ~ O M f m H ~ z o l l.:::.a;I"'n.o:::s':::tTi;:'tutesfor Environmental esearch a o . - I 138, May1967), pp. 3-10.

62


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Scor1nAug. 19 A".. ,16. Wallace A.Develo ment:

R ~ d 1 0 Sets.Interference Pred1ction ModelEffect Stud of Tactical PM

6 17. TM " M 486 M 6, Loc. Cit.18. A. Bruce Carlson.duct10n to 81 nals and Noiseork: McGraw- i 1 Book Co.,19. lW 20. Ibid21. TM 11-486-6. Ope Cit p . 1M 4.22. Holbrook, Loo. Clt.23. Holbrocll. Ope CU , p. 60.24. Holbrock. Ope Oit . , p. 3.25. L.A. Follet t , Stud of Informat1on xc e betweeWar Game d Electrom et c Com at t ctiv t es, Dept.of the 7. ice 0 the Chie 0 ommunioations M ectronics(Report No. 12, Contract No. DAM 36-039M SC-88537. 30 April 1964).p . 20.26. ~ . p. 22.Z7. IbH. 28. Heverly, .2:2 ....1 t . , p. 49.29. G. Foley, Performance AS!BSSmenl ot Commun1cationsSzstems, (Great Britian: Proourement EXecut ve, Ministry ofDefense, November 1972), p. 2.

i 97OT. p . G-71.31. TM 11-486-6. Op. Cit . , p. 5-1.32. Egli, O p. Cit ... p . 1384.63

, : : C . : ; ; o m m = u ~ n ~ i = c ; r a . : : t , ; l ; , i ~ o n ~ : : . l . = - = - ; = ' : ; : ' : '.....

30. Eleotrofor IW Analysig. U


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:n. l lU . 34. A. Blomquist, "The tatluence ot Roisture in theGround, Temperature and Terrain on Ground Wave Propagation inthe VHF-Band,M l ! I lr!a!ictions on Antennas and Propagation,(April 1958), pp. i ~ = t f i , 35. ~ . p.1 69.36. Heverly, Op. Cit. , p. 79.37. Ibid. , p. 60.38. Egli, Op. Clt. , pp. 1383.1391.39. Heverly, Op. Cit. , p. 51.40. Ibid.41. George Kennedy, ~ e c t ~ Q COmmunication Sls t "S .(new Yorks McGraw-H111 Book 0., f9701, pp. ~ 6 0 - ' 6 1 . 42. ~

44. Henry Jaslk, Antenna E n g l n e e r . n ~ Handbool' (NewYorks McGraw-Hill Book Co 190T1. pp. is.1 to lS-2 45. u.s. Army, S l ~ a l Reterence D ~ t a , U.S. Army SignalCenter and School (ST 1 1 - ~ 4 - 2 , Sept. 196 1; p. 1-22.46. U.S. Army, "Tactical Electronic Warfare Data S h e e t , ~ U.S. Army Command and General Statf College. (R 1601, 1975).47. Johnson, Op. C l ~ . pp. 30-293.

64


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8IBI10GitAPHY

3 u l ] i n ~ t o n , Kennsth. "Radio PropoGation Vgriaticns atVHF 'md U ~ T F , " F r o c ~ e d i n f s of the I .R.E., 38:27-32,January 1950.

Carlson, Al bin B. Cornmunloatior; 3;vstems: An Introductionto Signal and Noise in Electr ical Communication.New York: McGraw-Hill Book., 1968.Carroll , John M. Secrets of Electronic Espionage.

N e York: E.P. Dutton and Co., 1966.Chandler, D.S. The Probability Scoring Model for ScorinK)Voice Communications Reception. Bell Aerosystems Co.,Aug. 1966.Department of the Army. Trvt 11-486-6, ElectricalCommunica t i on SJrstems Engineering Radi o. Washington:Government Printing Office, August 1956.Bgl l , John J . "Radio Propagation above 40 j\':C: Over I r r e , ~ u l a r Terrain," Froceedings of the I .R.E. , 45:1383-1391,October 1957.Ell iot t , D.N. Computer Nldel for the SimUlation ofTactical Signa] EnVironments, Electronic DefenseLaboratories, December 1965.Emmons, A.'';. FH Capture Ferfor':1ance and i t s Consid>?ratlonin Receiver Design. ~ I i d e d Missle Research DiVision.Los Angeles: Ramo-liooldridge Corp., July 1957.Foley, G. PerforT-ance Assessment of Communicatl-ons ;;ystems.Signals Research and Development Establishment,

G r e ~ t Britian, November 1972.Grant, E.C. EI:,ctric Field-Altitude Variations in VHFFropa"ati'Jn and a Survey of the Effects of IrregularTerrain. Dept. of the Army, Signal Corps Laboratories,Tech Memo. 76. washington: Government Printing

Office, April 1960.HaClsl:sr, Donald H., Ed., Ccmmunication S stem Eni2:ineerillH3.ndbook. New York: t!JcGraw-Hill Book Co., 197 .pverly , J . Rosso R a n ~ e , ~ o b l ] i t y , a ~ Transmissic,n ReJ ~ a b l l l t y

? ~ c t c r s for Division Comllunications. Dept. ofL;cc Ar'Uy, Army Research Gffl-ce, Tech. /JIemo.'l.AC(O,10)-,:,-408, ,June 1962.65


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Fl,:)l hrook, > r : ~ } '1 n ( ~ ' ; ~ ;\.. I n t f ~ 1 ' f 9 : r 8 ~ I C 8 Fredlc t ' j on Volle: 1 ) t ~ v e l ( ) I J m e r i t : Cn-C1lallll',j ' j , , ' ture ;:;ffect Stud of Tactic;al FM RadioSets , Bell Report No. A70009-12" July 19 ' .Eellry, ":'.1. Antenna Enl;1neering Hand book. New York:~ r c G r a w - H i l l Soak Co., 1961.

Kennedy, Gec'rge. ElectronJ.c Communication Systems. Neli York:' ' 'cGraw-Hill Book Co., 1970.Lonzley. ~ . G . Comparison of I r 0 r ~ ~ a t l o n Measurements WithPredic te ; Values in the ?C to 10.000 14Hz R'tnge.TT.S. Dept. of Commerce, Environmental Science Servic"s,rJ'nin., Tech. Rept. ERL 148-IT3 97. 'rI'ashineton:

C ~ o v ~ r n I D e n t Frintint:; Office, Jan . 1970.r1agnuski, 'enry. "JamminG of Communication Systems Using

"' ' ' , A..\l and SSB Modulation, II IRE Transact ion on Mili ta ryElec t ronIcs , M1L-5 (January 1961 ), 8-11 .ran te r , Phi l ip F. CommunicatJ.on Systems DiPislgn. 1 st Ed.New York: McGraw-Hill 300k Co., 1972.SchlesinGer, Robert

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