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NOTICES

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The findings in this report we not to be construed as anomeical Department of the Army position, unless so dveig-nated by o~or authoriled documents.

The citation of trade names and names of manufacturers inthis report is not to be construed as offlcial Ooverementindorsement or approval of commercisl product. or servicesreferenced herein.

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Disposition

Destroy this report when it Is no longer needed. Do notreturn it to the originator.

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Reports Control Symbol OSD-1366

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TECHrIWCAL REPORT oOM-- 4133

UTILIZATION AS RF-ANTEN1AS OF LIVE AND OF LIFELESS SSTRUCTMRES IN NATURAL AND IN MAN MADE JUIMLES

BY

K. Ikrath, K. J. Murphy and W. Kennebeck

SELECTROMAGNETIC COMPATIBILITY TECTNICAL AREA

COMMUNICATIONS/ADP LABORATORY

DA Work Unit No. 136 62701 A448 06 18

June 1973

DISTR IBUTION STATEMENTApproved for public relusea dlsributlcn unlligliol.

US ARMY ELECTRONICS COmmANDFORT MONMOUTH, NEW JERSEY

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ABSTRACT

Natural foret trees, man-planted shade trees, metal lantern poles andbuilding structures were utilized as efficient HF radio antennas with theaid of Hybrid Electromagnetic Antenna Couplers (HE4AC's). The performanceof live trees and of inanimate metal structures as antennas is comparedwith the performance of conventional HF whip and dipole antennas. Similarpractical data are given on the LF radio signal emission capabilities of .huge steol-concrete buildings and on LF radio signal diffusion via electricalpower and water distribution systems in sutburban areas.

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TABLE OF CONTENTS

Abstract ii

List of Figures iv

1. Introduction I

2. Discussion 1

A. Control of Directivity of RI Signal Radiation from 1a HD(AC Coupled Forest Tree Array

B. HD(AC-Tree Load Impedances 13

C. Live Wooden Trees versus Dead Metal Lantern Poles 18

D. The Utilization of Buildings, Water and Power Lines 52as RF Antennas and Transmission Media

(1) HF Signal Emanation and Reception by Building 52Structures

(2) LF Signal Eanation and Reception via Urban 57

Media

3. Summary and Conclusion 62

4 . Recommendations 68

5. Acknowledgments 68

6. References 68

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LIST OF FIJURL-3

Figue No. page

HD(AC Toroid Coupled Tree Array 2Wayside Test Area Sept., Oct. 1972

2 HIMAC Coupled Tree Circuit (..o.e-up View) 3Wayside Teat Area Sept., Oct. 1972

3 Transmitter Setup for T-w!n Tree ArrayWayside Test Are& Sept., Oct. 1972

4 Phased HEMAC Toroid CruiiJd iJin Tree 6Transmitter Array M51. ? Lg.:'-Wayside Test Area Stept., Oct. 1972

5 Whip Bqulppe.i Recei.,er V Lihir2': 7

6 BK - Heterodyri Voltmeter T:T,3 2007 in the 8Receiver Vehicle

7 Map of XMTR (X) and Receiver Locations 91 to 12 - Measuremen.•s of Radiiation Patternsfrom HEMAC Coupl'd Twin Tree UI;TR ArrayFt. Monmouth Area Oct. 1972

Radiation Patterns of HEMAC Coupled Twin 10Forest Tree XMTR Array. (Tree #1 - On,Tree #2 - Off, Tree #1 Ow'f, Tree #2 - On)Ft. Monmouth Area Oct. 1972

9 Radiation Pattern of HEKAC Ccupled Twin Forest 11.Tree XMTR Array (Tree #1 - Cn, and Tree #2 - On;,6,. - 0°Ft. Monmoiuth Area Oct. 1972

10 Radiation Patterns of HE4AC Coupled Twin Forest 12'Tree XKTR Array (Tree #1 - On and Tree #2 - On;AW q" 900, 1800)Ft. Monmouth Area Oct. 1972

11 CW and AM Voice - 4.650 MI7{z £ransmission Test 14Data (Twin Tree XMTR-Array - Wayside Area toStation AD2fL Evans Area) Oct. 1972

12 HD(AC-Toroid Input Resistance and Reactances 15(On-Off Tree) h - .5mWayside Test Area Sept. 1972

13 HEMAC-Toroid Input Resistance and Reactances 16(On-Off Tree) h * 1.25mWayside Test Area Sept. 1972

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LIST OF FIGURES (Continued)

?iaure No. pg

14 HAC-Toroid Input Resistance and Reactance 17(On Tree h - 2.4m)Wayside Test Area Sept. 1972

15 HAC-Toroid Rc/r Matching Tuning Nomogram 19

16 PF-7 4 Whip Input Resistance and Reactance 20Wayside Test Area Sept. 1972

17 HMOC-Toroid Plus Metal Lantern Pole Input 21Resistance and ReactanceHexagon Area April i.T'

18 PRC-74 Whip and HEMAC Coupled Tree Setup 22(10.803 MHz Transmission Hex to Evans Area)Hexagon Area Feb. 1973

19 PRC-74 Whip and HEMAC Coupled Lantern Pole "3Setup (10.803 MHz Transmission Hex to Evans Area)Hexagon Area Feb. 1973

20 HEMAC Coupled Tree Setup (Close-up View) "10.803 Miz Transmission hex to Evans AreaHexagon Area Feb. 1973

21 HEMAC Coupled Lantern Pole Setup ý5(8.050 MHz Transmission Hex to Evans Area)Hexagon Area Nov. 1972

22 EM{AC Coupled Lantern Pole Setup 26(10.803 MHz Transmission Hex to Evans Area)Hexagon Area Feb. 1973

23 HEKAC Coupled Lantern Pole - Matchbox 27(Close-up View)Hexagon Area Feb. 1973

2P HEMAC Coupled Short Wooden Pole Setup 28(10.803 Ml{z Transmission Hex to Evans Area)Hexagon Area Feb. 1973

25 HDMAC Coupled Jeep Setup 29(10.803 MHz Transmission flex to Evans Area)Hexagon Area Feb. 1973

26 Station AD2XL 31Evans Area - (Antennas)

vIVD

LIST OF FIGUTRES (Ccntinued)

Figure No. Pae

27 Station AD2XL 32Evans Area - (Receiver)

28 Voice and CW Radio Transmission Test Data 33Hex to E%,ans Area (Whip, HFIAC-Poles)Nov. 1972 to Feb. 1973

29 Voice and CW Radio Transmission Test Data 34(Whip, hM4AC, Pole, Tree) Feb. 1973

30 Voice and CW Radio Transmission Test tata 35Hex to Evans Area (Whip, H7,!AC, Pole, Treeand Twin HE4AC-Pole) Feb. 1973

31 Twin HEMAC Coupled Lantern Pole Setup 36(8.034 Mz Transmission; Hex to Evatus Area)Hexagon Area Feb. 1973

32 Aerial Tramway Gondola 8.25 MH?; 'M4TR above Tree 38and Lantern Pole Receiver SetupHexagon Area April 1973

33 Aerial Tramway Gondola 8.2,.5 tHz )TR 39Approaching Tree TopHexagon Area April 1973

34 Aerial Tramway Gondola 8.25 MHz KMTR above 40PRC-74 Whip ReceiverHexagon Area April 1973

35 Recording of 8.25 Mlz Output Voltage Amplitude 41from HE4AC Coupled Lantern Pole (HL) versusUpward Movement of Aerial Tramway GondolaRIE4AC PMTR (X) 9 April 1973

36 Recording of 8.25 MHz Output Voltage Amplitude h2 Sfrom HEM4AC Coupled Lantern Pole (HL) versusDownward Movement of Aerial Tra., way GondolaHEMAC XDTR (X) 9 April 1973

37 Recording of 8.25 M1z Cutout Voltage Amplitude 43from HEKAC Coupled Tree (HT) versus UpwardMovement of Aerial Trarway GondolaHEKAC XMTR (X) 9 April 1973

38 Recording of 8.25 MHz Output Voltage Amplitude 44from HEMAC Coupled Tree (11T) versus DownwardMovement of Aerial Tramway Gondola pHEMAC XMTR (X) 9 April 1973

vi

p

LIST OF FIGURES (Continued)

i-e No. .

39 heeording of 8.25 M1z Output Voltage Amplitude h5from 1M(AC Coupled Tree (HT) versus Movementof Aerial Tramway Gondola RD(AC XMTR (X)Upward from Above Tree to Roof of Hexagon

9 April 1973 S

40 Recording of 8.25 Mz Output Voltage Amplitude 46from EMAC Coupled Tree (NT) versus Upward(Left Part) and Downward (Wht Part) Movementof Aerial Tramway Gondola X4ACO D (X) .)

9 April 1973

41 Reoordirg. of 8.25 M4z Output Voltage Amplitude 47from a PRC-74 Whip (W) versus Upward (Left Part)and Downward (Right Part) Movement of AerialTramway Gondola NWC XMTL"R (X)

9 April 1973

142 Recording of 8.25 MHz Output Voltage from A 48PRC-74-Whip (W) verous Down Ward Movement ofAerial Tramway Gondola Whip XMTR (X)

16 April 1973

43 Recording of 8.25 MUz Output Voltage Amplitude 49 Sfrom HERAC Coupled Tree (HT) versus DownwardMovement of Aerial Tramway Gondola WhipXMTR (X) 16 April 1973

44 Recording of 8.25 MHz Output Voltage Amplitude 50from HEMAC in Air (HA) 18 Inches above Ground Sversus Downward Move of Aerial Tramway GondolaWhip XMTR (X) 16 April 1973

45 Recording of 8.25 mHz Output Voltage from A 51PRO-74-Whip (W) vvrsus Down Ward Movement ofAerial Tramway Gondola Whip XMTR (X)

16 April 1973

46 Window Dipole (11.950 MHz Transmission Hex to 53Evans, Freehold, Oceanport, Hexagon(Room 4D323) April 1973

S147 1F/C Coupled Window Frame (11.950 0 514

Transmission Hex to Evans, Freehold, Oceanport,Hexagon Room 4D323) April 1973

48 LF - )0R Solenoid on M-109 Truck Roof 58

49 LF-XMTR Setup in M-109 Truck Van 59

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LIST OF FIGURE3 (Continued)

Mia.re M_. page

50 LF-)GR Truck Under Power Line at Camp Charles 60Wood Motor Pool (Location #1 fcr 85.2 kHzTransmission Test) 22 Feb 1973

51 Map - Hexagon LF-VLF Receiver Station and 61 iLF-XMTR Truck Locations #1 and #2(85.2 kHz Transmission Test) 12 Feb. 1973

52 LF - XMTR Truck at Green Acres Office Building 63(85.2 kHz Transmission Test) 12 Feb. 1973

53 Record of 85.2 kHz Signal Levels Received by 64LF-VLF Station in the Kexagon Building

12 Feo. 1973

54 Pick-up by Ferrite Loopstick of 80 - 90 kHz' 65Signals from Water Cooler in Hexagon Bldg.

55 Pick-up by Ferrite Loopstick of 80 - 90 kHz 66Signals from Heating Radiator in Hexagon Bldg.

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A, .

1. INTRODUCTION

The capability of vegetation and of trees to serve as radio antennashas been reco nized as early as 190 by Major George 0. Squire of the US ArmySignal Corps. NM. G. Squire's ideas of using trees as radio antennas havebeen realizud in practice with the aid of a flexible toroid shaped HybridElectro-Yo netio Antenna Coupler device called a HEHAC.e As a result offield ,xperiments and radio transmission measurements which were carried outwith conventional hardware antennas and with HEKAC coupled trees in tropicaljungle forests in the Panama Canal Zone, it became evident that jungle treesserving as MF and HF antennae are able to overcome the obstructing effectsof jungle vegetation relative to conventional antennam on RF comunications.

3

Furthermore, measurements of MF •d of HF radiation patterns from forehýtrees in the Ft. Monmouth, N.J. area and in the Lebanon, N.J. State Forest'revealed that in particular the HF radiation pattern directivities arecaused by "dominant natural tree loops" that is by the parasitic array-likeinteraction between the HgMAC coupled tree and nearby neighbor trees.However, as stated in the first part of this report, the control of thedirectivity of RF emissions from forest trees need not be left to orienta-tions of the natural dominant tree loops at a chosen transmitter (XMTR)location in the forestj the directivity of RF signal emissions via foresttrees can be controlled by the radio operator with the aid of phased HUIACcoupled tree arrays. Yet, whereas control over the directivity of the RFradiation becomes a matter of human effort, the control over the rangeof applicable practical radio frequencies remains a function of the materialand structural heterogeneity and anisotropy of the forest vegetation.Corresponding implications with regard to matching conventional radio Stransmitters to the impedances of forest trees and the surrounding under-brush vegetation are discussed in the second part of this report. In thethird part, the search for practical upper frequency limits is pursued in-directly by comparing the performance of trees as radiating antennas withthat of metal lantern poles of comparable dimensions. This comparison oflive structures of natural Jungles with lifeless structures of urban Junglesprovides the transition to the fourth part which describes the utilizationof steel and concrete structurem, buildings, water and power lines etc.,for radiation and transmission of RF signals in "urban Jungles". Ephasisis placed here on the distinction between RF radiation from buildings andRF diffusion inside buildings and on the corresponding methods and meansfor RF signal emission and reception.

2. DISCUSSION

A. Control of Directivity of RF Signal Radiation from a HEMAC CoupledForest Tree Array.

The pair of forest, trees which served as transmitting antenna and Swhich will be referred to as twin tree array is shown in Fig. 1. The treetrunks are four meters apart and have a circumference of 1.85 and 2.4 metersmeasured at 1.5 meters above ground. A close-up view of the match box andHEXAC toroid circuit on one of the trees is seen in Fig. 2. A picture ofthe X74TR setup in a shelter in the vicinity of the trees is given in Fig. 3.

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The block diagram of the XOTR circuit is shown in Fig. 4. The HD(AC coupled V0trees are connected with the Y14TR setup in the shelter by nine and fifteenmeters long coaxial cables. The XMTR setup consists of a pair of GlobeAmateur Radio XMTR Sets which are operated in the AM and CW mode. The VFOinput of the Globe )MR Set No. 1 is connected via a capacitive voltagedivider to the output of a crystal (XTAL) controlled oscillator. The inputof the other Globe XMTR Set No. 2 is c,'rnectei to the XTAL controlledoscillator via a delay line made from a 36 meter long RO-58 cable with tapsat four meter spacings. The phase difference between the VFO input signalsof Globe XMTR Set No. 1 and No. 2 is adjusted in steps by plugging intodifferent taps of the delay line; smooth fine adjustment of the phase isobtained with a tuning capacitor which can be connected to the dummy loadend of the delay line or across an unused tap of the delay line. The phasedifferences of the resultant XMTR output. voltages were displayed on anoscilloscope in form Lissajou patternz. For this purpose, the x and the yinputs of the o.ioilloscope were coupled to the connections of the No. 1and No. 2 tree feed cables and the No. 1 and No. 2 Globe XMTR outputs.The maximum CW power output from these trai ;;mitters was determined to be12 and 16 watts. Radiation patterns were measured at a frequency of 4.650Milz with a vertical 5 foot 10g whip antenna that wa3 mounted on a truckshelter and connected via RG-58 oablc to the untuned high ixnpedance inputof a BK-2007 Heterodyne Millivolt Metar. Tho, whip eq'ipped truck and the •BK,.0O7 meter are shown in Figures 5 and 6. On the map in Fig. 7 are markedthe L•TR location in the Wayside N.J. to

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of phased forest tree arrays may be judged not only by the directions ofthe radiation maxima but also by the overall shapes of the ra.ation pat-terw iclud2n the directions of minima and of nulls and by thn data inFigure 11. In Figure 11 is shown the signal plus noise and the noise levelsreceived at station AD2XL in the Evans Area, seven miles to the south, andby whip equipped vehicle at Colts Neck, three miles to the west, fromthe Wayside Forest XMTR location. These signal plus noise levels are givenin oonnection with the XXTR phasing and the corresponding Liesajou patternsas displayed on the scope. The strong coupling between the trees isreflected by the parasitic current levels of 0.55 and 0.5 Amp RF in theO-OFF states of the Globe No. 1 and 2 XDTR sets. This kind of mutualcoupling becomes much -itronger when a pair of HE(AC's is coupled. to one andthe same tree. Such a HD(AC-tree setup was tried out during initial experi-ments with tree loops so as to optimize sky wave radiation buý this attemptfailed because of the strong mutual coupling and resultant difficulties inkeeping adequate power match while varying the phasing.

As pointed out before, the mutual coupling between different treesin a forest tree array offsets to some extent the efficient utilization ofthe available XMTR power; however, considering the overall performanceof the twin forest tree array as described by the radiation patterns andthe data in Figures 8 to 11 it is evident that the original objectiveswere realized, in that control over the directivity of RF radiation hasbeen taken from the dominant natural tree loops and handed to the radiooperator. Thus we nay now turn our aýtention to other factors that affectthe efficiency of operation of forest trees as antennas, namely the HDMC-Tree load impedances as fwictions of frequency which are the topic ofSection B of "uhe discussion.

B. HT!4AC-Tree Load Impedances.

The efficient utilization of forest trees as radio trano-4tterantennas depends primarily on the ability to match the transmitt outputimpedance to the input impedances of HEMAC coupled forest trees. Possiblesolutions of this matching problem depends on whether the transmitter isequipped with variable output impedance controls and whether the XMTR toHEIAC-Tree connection can be made very short in terms of wave length orwhether the HMC-Tree load circuit impedance must be powered from a sourcewith a fixed output impedance, such as presented by a random ler4th ofcable.

In the first case a fixed impedance transformation network can bedesigned which within certain ranges of frequencies and impedance ratioswill provide a satisfactory match between a viriable transmitter outputcircuit and tuned HEMAC-Tree load impedances, In the second case a variableHEDAC-Tree tuning and impedance transformation circuit, referred to in thefollowing as match box, is required.

Typical IEMAC-Tree impedances as functions of frequency which mustthen be matched to nominal 50 Ohm source impedances are shown in Figures12 to 14. The resistance R and reactance X versus frequency curves inthese figures were measured with a HEKAC on tree No. 1 of the previously

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described twin tree array. For these measurements, the flexible I0AC toroidwas mounted on a rigid plastic ring to maintain the same shape of the HEKACwhen used on and off the tree. Referring to the R and X in Figures 12 and13 one recognized first of all that HWC impedances off the tree in airand on the tree are drastically different. In air above the ground theHEMAC reactance is inductive below and capacitive above the sharp resonanceat about 9 MHz. On the tree several transitions between inductive andcapacitive regimes occur betweon 8 M!z and 14 X•z. The corresponding reso-nances are displayed by the relative maxima of the resistance curves atabout 9 MHz, 11 MHz, and 14 MHz. The height above ground of the HEKAC onthe tree influences the shape Lnd distribution of the relative maxima ofthe resistance and of the corresponding zero crossings of the reactance;apparently increasing the height of the HMEAC above ground tends to eliminatethe capacitive impedance region around 9 MHz as seen by comparing Figures12 and 13. The operating frequency range obtained with capacitively tunedmatching circuits is then increased accordingly. The peculiar resonances ofthe EHAC on the tree in conjunction with the capacitively tuned matchingcircuit explains the previously observed abrupt decays of radiation fromdifferent trees at frequencies between 7 and 1i MHz. Below the frequency oftransition from the inductive to the capacitive regime the matching andtuning of HEKAC coupled trees is accomtlished with two variable capacitorsC and C0 in accordance with the HEAC R./r matching nomogram in Figure 15.Rc and r refer to respectively the constant source resistance and the

{EMAC-Tree load resistance. The optinim matching conditions given by thenomogram correspond to the critically damped resonance mode of the circuit.In practice this optimum match is achieved by maximizing relative power andby minimizing the SWR. For this purpose a simultaneously power and SWRindicating meter has been incorporated into the original HEMAC matching box.Evidence that the tuning of the HEMAC-Tree transmitter circuits requiresless skill than tuning of the PRC-74 whip )DMTR circuit may be deduced fromthe input resistance R and reactance X of the PRC-74 whip which are plottedversus frequency in Fig. 16. Furthermore, since the previously mentionedexperiments in the Panama Canal Zone and in the Lebanon, N.J. State Foresthave shown that in the 60 to 80 meter wave length range the center coilresonated and 2.7 meter long PRC-74 whip can hardly compete with large 20to 30 meter high forest trees, smaller trees and metal lantern poles weresubsequently put to work as antennas at shorter wave lengths; as seen inFigure 17 the poles present to the HMOC a similar load with fewer resonances.The resultant implications with regard to RF communications in natural junglesof live vegetation and in urban Jungles of dead steel and concrete willbecome evident in Section C.

C. Live Wooden Trees versus Dead Metal Lantern Poles.

The relative dimensions of a typical smaller tree and of a 9 meterhigh metal lantern pole in relation to the PRC-74 whip antenna are seenin Figures 18 and 19. Close-up views of the PRC-74 Rndio Transceiver setupswith HEMkC coupled trees and metal lantern poles in the Hexagon-Ft. Monmoutharea are shown in Figures 20 to 23. Figure 24 shows a HERAC PRC-74 trans-ceiver setup on a short 'wooden pole that protects one of the fire hydrantsin the Hexagon yard. A similar setup with the HFMAC on the roof of a jeepis seen in Figure 25. Voice and keyed CW signals emitted from these PRO-74

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29

radio transceiver setups on frequencies between 5.5 Mz and 11.0 MHz werereceived and measured at station Afl2XL in the Camp Evans Aria (Bldg. T-113)about seven miles south from the Hexagon-Camp Charles Wood Area. Picturesof this station are shown in Figures 26 and 27. One may note that thehorizontal wire doublet antennas of the station are oriented for optimalreception of vignals arriving from east and west rather than from north and (f)south. In one case the emitted signals were also monitored and measuredinside the Hexagon building, in Room 4D423, using the BK-2007 heterodynevolt retor and a short whip antenna. The resultant data are tabulated inFigures 28 to 30. A comparative inspection of these data leads to the Sfollowing conclusions: The HOWAC coupled lantern poles outperformed allother radiators at all times &nd on all frequencies between 6 and 11 MHz.Radiation from the PRC-7L whip is from 2 dB to 12 d0 lower than that fromthe lantern poj1s. The performance as antennas of the HE4AC coupled smalltree and of the jeep are about equal to the performance of ahe PRC-74 whipantenna; the tree being slightly better than the whip in the majority of Scases and particularly then when the noise and RFI levels at the receiverstation were relatively high. Radiation from the HE4AC by itself, with theHEXAC placed on a wooden table and on the short wooden pole (Fig. 24) Isfrom 10 dB to 18 dB lower than that from the lantern poles.

Similarlly to the previously described attempt to use a twin HEMACcoupled tree to control ground and sky wave emission, a transmission testwas carried out with a twin HDKAC coupled lantern pole as radiator.However, having learned from the past, no attempt was made to power thetwin HEKAC coupled lantern pole from two phased transmitters. Instead asseen in Figure 31 a single PRO-74 set used as a XDTR feeding directly eitherthe upper, or the lower HDQAC such that the lower and upper HEA.C act asparasitic elements, such as the reflective and directive elements of a Yagi 0antenna. Furthermore, both HD(ACs were fed in parallel and tuned formaximal radiation. The results, (Table - Fig. 30) show that the latter caseis the worst of all, so much so that the signal is 6 dB and 3 dB duwnrelative to the first and second cass.

Considering the evident superiority of the metal lantern poles asantennas relative to the approximately equal performance of the small treeand the PRC-14 whip antenna, one may wonder to what extent the results ofthese ground to ground transmission tests were influenced by differencesin the ground and sky wave radiation emissions. In this connection it shouldbe pointed out that both the overall radiation efficiency, as well as theground and sky wave emission mechanisms, are greatly influenced by the groundand the grounding conditions of the respective radiators.

In order to obtain an idea on the spatial distribution of radiation.for the design of subsequent tests and measurements by airplanes an "aerialtramway" was set up between the Hexagon roof and a lantern pole at themovie theater east of the Hexagon. The nylon string of the aerial tramwaywas suspended in such a&way that one of the shade trees and a lantern polewere located about half way beneath the aerial tramway. The gondola of thetramway was moved upward towards the H.xagon roof and downward towards themovie theater by nylon string@ running through a pulley at the Hexagon roof.

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36"

Pictures of the aerial tramway - gondola experimental setup are ahown inFigures 32 to 36. The gondola carried a small 1 watt RF transistor DTrRoperating on a frequency of 8.25 MNz. The experiments were made with thesmall HD(C e011 that can be seen in the pictures (Figs. 32 to 34) and witha 1 meter long vertical wire as XDTR antennas. The experimental setups andtest objects such as lantern pole, tree, PRC-74 whip and the H(AC byitself are described by the illustrations above the recordings in Figures 35to 4S. These recordings give the output voltages from the test objects asfunctions of the position and movement of the XM gondola above. Therecordings were made with a TR-722 recorder connected to the recorder outputof the BK Heterodyne Voltmeter. Pulling the gondola XMTR upward was moredifficult and slower than pulling it don-ward with the ends of the stringson the parking lot between the Hexagon and the movie theater and with thepulley located on the Hexagon roof. The upward and downward recordingsare distorted since the recording speAd is not synohroniued with upwardand downward speeds of the transmitter gondola. Furthermore, the batteryof the gondola - XMTR was running down during the tests; consequently, thepeak voltage outputs from the different test objects reflects to some extentthis drainage of the XMTR battery. It is also necessary to point out thatthe recorded output voltages are indicative of essentially the interactionof the test object with the gondola D(TR'a near fields rather than with its'radiation field. Nevertheless, insofar as different near fields correspondto different radiation fields, the recordings in Figures 35, 36 and 37,38for respectively the lantern pole and the tre. prove that the primaryobjectives of the experiments were achieved. The lantern pole and tree,coupled by identical HEKACs and immersed into practically identical BFfields from the HM4AC antenna equipped gondola XHTR, deliver drasticallydifferent recordings. The lantern pole output is double-lobed and has a * *deep null when the XTR gondola is directly over it so that the resultantpattern is double-lobed. The tree output is broad with a flat maximum ofthe pattern when the gondola XDrR is diroctly above the tree. The finestructure of the tree output is seen in the recording in Figure 39. Thewiggled fine structure is caused largely by the jerky movement and windinduced swinging of the gondola XHTR. The previously mentioned relativedistortion of upward and downward recordings is clearly seen in Figure O40for the tree case. Similarly, Fig. 41 shows the upward and downward recordsfor the PRC-74 whip. Considering that the whip and metal light pole are"vertical electrical rod anternals" the completely different shapes of thePRC-74 whip and of the lantern pole recordings (Fig. 41 and Figs. 35, 36)are surprising. The null of the lantern pole record with the gondola HD4ACXMTR directly above the pole agrees with expectations founded on idealizedgrounding conditions. The flat maxima in the whip case under the same con-ditions could be reconciled with the existence of entirely different round-ing conditions for the PRC-74 set in conjunction with the influence of thecenter coil resonator on the induced whip current distribution, Similarrecordings obtained with the one meter long vertical wire instead of theHDAC coil as gondola JOTR antenna are shown in Figures 36 to 39. In spiteof the greater susceptibility of the vertical wire XMTR to wind and jerkymovement induced deviations from vertical orientation and correspondingperturbations of the polarization of the emitted fields, one recognizesparticularly in the lantern pole recordings the deep fadings of the outputvoltage when the X0TR is above the pole.

37

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RE(,ORDING OF 8.25 MHz OUTPUT VOLTAGE AMPLITUDEFROM HEMAC COUPLED LANTERN POLE (HL) VERSUSUPWARD MOVEMENT OF AERIAL TRAMWAY GONDOLAMEMAC XMTR(X) FG35APRIL 991973

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RECORDING OF 8.25 MHa OUTPUT VOLTAGE AMPLITUDEFROM HEMAC COUPLED LANTERN POLE (HL) VERSUSDOWN WARD MOVEMENT OF AERIAL TRAMWAYGONDOLA HEMAC XMTR (X)APL913

FIG. 36

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RECORDING OF 8.25 MHz OUTPUT VOLTAGE AMPLITUDEFROM HEMAC COUPLED TREE (HT) VERSUS UPWARDMOVEMENT OF AERIAL TRAMWAY GONDOLA HEMACXMTR (X) AP RIL 9,197 3

FIG. 37

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RECORDING OF 8.25 MHz OUTPUT VOLTAGE AMPLITUDEFROM HEMAC COUPLED TREE(HT) VERSUS DOWNWARDMOVEMENT OF AERIAL TRAMWAY GONDOLA HEMACXMTR (X) APRIL 9, 1973

FIG. 38

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RECORDING OF 8.25 MHz OUTPUT VOLTAGEAMPLITUDE FROM HEMAC COUPLED TREE (HT)VERSUS MOVEMENT OF AERIAL TRAMWAY GONDOLAHEMAC XMTR (X) UPWARD FROM ABOVE TREE TOROOF OF HEXAGON. APRIL 9,1973

FIG. 39

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RECORDING OF 8.25MHz OUTPUT VOLTAGE FROMA PRC-74-WHIP(W) VERSUS DOWN WARD MOVEMENTOF AERIAL TRAMWAY GONDOLA WHIP XMTR (X)

APRIL 16,1973

Fig. 1s2

48 .

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RECORDING OF 8.25 MHz OUTPUT VOLTAGEAMPLITUDE FROM HEMAC COUPLED TREE(HT)VERSUS DOWNWARD MOVEMENT OF AERIALTRAMWAY GONDOLA WHIP XMTR(X)

APRIL 16,1973

Fig.- 4g)

49

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RECORDING OF 8.25 MHz OUTPUT VOLTAGEAMPLITUDE FROM HEMAC IN AIR(HA) 18 INCHESABOVE GROUND VERSUS DOWNWARD MOVE OFAERIALTRAMWAY GONDOLA WHIP XMTR (X)

APRIL 16, 1973

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RECORDING OF 8.2w MHz OUTPUT VOLTAGE FROMA PRC-74-WHIP(W) VERSUS DOWN WARD MOVEMENTOF AERIAL TRAMWAY GONDOLA WHIP XMTR (X)

APRIL 1691973

Fig. Ii$

51S

Hence, there is no Jcuoi'. .at rt."vazn .L :rn.3 '.r ,'"from liante.•n poles Is *st be different, particu larly- -i-h rs-: dand sky wave radiation. Resultan.t Lmplica:,Ion• for ground "o ac r *c.-un±- r..cations will be investigated in future testj ualng an airplane for thispurpose. The fact that the metal !an'err. -ý1en are plantS -,f urban junglesand wer : tr ,;ork !13 eff-cient radio antennas leads deeper into the urbanJu-.n;le and int7 -h- :'il'nwln_ technical irea of application,

"7h,2 i>iing. . and Powr Lines azý RF Antennas

(.) •' Signal anatra.1jon and •qeceop.ion by Building Structures.

in the introduction it was -ointed out that the RF corunL.a-"-ino in urban J-ngles involves principally RF induction, conductio.. -Indradiation in conjunctlon with diverse structures. Considering the .•.-uc-rural and material similarities between conventional whip type antennas andmetal lantern poles, the previously described utilization of lantern polesa3 antennas s'ems obv.ous. However, ýhe use of buildings and of specificparts of buii..iitgs is not so obvious.6 The reasons for this will becomeevident ý.y comparing the picturei in Figures 16 and 47, The nicture inFig. '3 shows a conventional horizontal wire dipole antenna whiuh is mounteion to the glass window panes in Room 4DL23 in the Hexagon building, Thisdipole is made from and connected with a 300 Ohm twin wire line to theantenna terminals of a PRC-7h set. Thanks to the variable output innadanceof the PRC-74, the window dipole could be matched to the set dithin a narrowfrequency range at around 11.950 MHz. The picture in Figure 47 shows 'hesame windows or-th their metal frame couplmei to another PRC-74 radio set -:-aa short piece of FO-58 cable and the match box and HEMAC circult. Therelative performance of the window dipole and of the HPAC coupled windowframe as an REF antenna was measured in two waya:

(a) On March 16th, 1973 the levels of the emitted ii,95Z ý!HzC1 and voice signals were compared as received at station AD2XL in the6vans area from the window dipole and from the HEKAC coupled window fram=,",owered from the PR,-74 sets, with respectively 11.5 and 12.0 watts RFpoJer. Defore 1100 hours local .. "o gnal plus noise 'o noise raticreceived at the Evans station from tne window dipole and from the H1MCcoupled window frame were 20 dD/15 dB and 25 dB/15 dB, After 1100 hoursbroadcasts from BBC London, England interfered with further measurements onthis frequency, i.e., the optimum frequency for the window dipole and 3ub-sequent transmissions to the Evans station were carried out on 11.938 1't''.z.

On the previous day, the 15th of March 1973, zpiilai'transmissions from the HEKAC coupled window frame to Evans were made withthe HEUAC coupled to the upper and the lower part of the window frame atvarious frequencies between E and 12 M1z. In spite of the dense occupancyof this frequen-y band by powerful 11? stations from all over the world,signal plus noise to noise ratios could be measured on 10.540 MWz with maxi-mal 18 dB/lO dB and minimal 22 dB/18 dB a't different times of the day. Thelatter value reflects not only higher RFI noise levelp but aloo a lowerRF power output from th6 PRC-74 set as its battery power dropped towards theend of the transmission tests. Furthermore, voice transmissions on 11.800MHz and 8.850 M1z were received intelligibly in the presence of strong RFI.

52.

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(11.950 M'~z Transmi~ssionl He reproduction method topoideto Evans, Freehold, Ooeanport, bete do"~i.Hexagon Roomi 4Df323) April 1973

54S

S

(b) On 1ý, 16, and 17 April 1973 voice comuunicationsm range0tesstweremdewiththe driver of a truk vehicle who had the whip of hisPMO-74M got stioking out through the open window of the driver's cabin.Theme voie conications range tests were maWe in the western directiontowards Freehold, N.J., and in the eastern direction towards Oceanport, N.J.for the following reuont The windows of Room 4DW23 are on the westernside of the Hexagon building and look into the yard which is open towardsthe west and bounded in the north, east and south by th.3 completed partsof the buildin. On 13 April 197.3, an exploratory range test with the HD(ACcoupled window frame as antenna was made initially on 11.950 MHz.

However, during the test, at 1500 hours local time, theWest African Service of Radio Hilversum, Netherland began to interferestrongly with the test frequency. Switching consequently to 11.970 MHz,a clearly intelligible voice coimmunioations range of 6.5 miles.west fromthe Hexagon to the intersction of Highway 537 with Five Point Mile Road was Sobtained.

On 16 April 1973, a communications range - comparison testwas carried out for the window dipole and for the HDMAC coupled window frameon 11.960 MHz. The results of this range test towards the east of theHexagon, the direction blocked by the building, is tabulated.

16 April 1973 Test Data:

Window Dipole versus HIM.C-Window Frame XMTR

Mobi'le Station Hexagon Station Rm. 4D423

Air Mileage Window HE4AO-Windowfrom Hexagon Location Mole Frame

2.0 Ft. Monmouth Weak but Loud & clearreadable ,

3.5 Oceanport Out, covered Weak butPost Office up by noise ,intelligible

As pointed out before, RFI from powerful HF radio broadcast andcommercial stations becomes very severe in the Afternoon hours; similarlyRFI in the Hexagon building, particularly from the freight elevator nextto Rom 4D423 tends to be higher and more' frequent around noon and afternoon.For this reason the subsequent 17 April test runs east and west from theHexagon were made in the morning hours on 11.950 MHz. The results areshown on the following page.

55. . .. . .

- . .. . .

SI I l I ll 'n I !"! ' - m • l - - ; ,, - = _ _

17 April 1973 Teat Data,

Quality of Voice Transmissions from Window DipoleHM4AC-Window Frame

Mobile Station Hgx n Station Rm. 4D423

Air Mileage H1XAC-WindowEast from Hex. Location Window Dipole Frame

2.0 Ft. Mdnmouth Clear Clear

3•5 Oceanport Clear Clear,Post Office stronger

West from Hex.

3.0 Intersection Hwy 5,37 Clear Clear,Laird Road stronger

4.3 Intersection Hwy 537 Readable Readableand 34 (*) OK oK

6.5 Intersection Hwy 537 Much weaker Clear,and 5 Pt. Rd. but readable strong

8.5 Hwy 537 approach Readable Weaker, 4to Freehold (*) readable

(•) Power-tele 4iono lines overhead

The observation that voice transmm.ssions from the Hexagon window dipolewere received slightly utronger than from the HD(AC coupled w.nziow framewhen the receiver vehicle wys parked directly beneath telephone and powerlines deserves closer scrutiny with regard to the roles of polarization ofthe emitted RF fields. However, the teots prove beyond any doubt that theH!MAC coupled window frame is a highly efficient, unusual, and practically 0invisible XKTR and receiver antenna which can be tuned over a relativelylarge frequency range and that the structure and geometry of the buildinggives directivity to r rqFrdittiton from its windows.

The test results prove, furthermore, that RFI noise pollute6 buildingstructures can be used effectively for the reception of relatively weak 1Fsignals from the PRC-74 whip Pot in the vehicle in the Ft. Monmouth - .Ocean.ort and Freehold, N.J. area and from HF radio stations overseas.

Considering this performance as HF antennas of building stractures, itbecomes an obvious challenge to apply whole buildings for the transmissionand reception of such low frequencies and corresponding earth, water, and"urban Jungle" penetrating long radio waves for which the size of conventional

56v

S

anternna becomes prohibitive and on which man made and natural MFI noise tooexcessive for conventional moans and methods of RF communications. In thisconnection it becomes necessary to mention the transmission of inductively Smitted and repived LF signals along the Earle to Sandy Hook, N.J. USNavy Railroad,' and subsequent transmissions over 20 miles along the Eaton-town-Lakewood spur of the N.J. Central Railroad over a distarne of 20 miles,from the Charles Wood-Ft. Monmouth area to Whiting, N.J. In both cases themaxd.mal available RP-XMTR output was about 50 watts. During the measurementsof the signal decay with distance along the railroad tracks it becomesevident that in addition to LF signal ducting along the railroad tracks,radiation directly from the railroad tracks and or indirectly from adjauentpower and telephone lines must be involved. The subsequently describedexperiments were designed to further exploit both of these transmissionmechanims for clandestine type communications in urban jungles.

(2) LF Signal Eanatior. and Reception via Urban Media.

The transmitter for this purpose is shown in Figures 0 to 50.Fig. 48 shown the large RF solenoid wound on a fiberglas tube which ismounted horizontally on the roof of a M-109 trunk. This solenoid is poweredby a nominal 50 watt Kronhite Amplifier driven from an XTAL controlledfrequency synthesizer LF source. The picture in Fig. 49 3hows the RF meter Sand capacitive tuning circuit encased in a lucite box inside the truck andthe power amplifier circuit and output transformer on the shelf in the leftupper corner of the picture. (The large "OCHL" generators beneath the lucitemeter - tuning box were not used in these experiments). The emitted LF, CWand keyed OW signals were monitored in the truck with a scope. For thispurpose they were picked up with a small ferrite loop stick which is seen S 0mounted vertically in front of the window.

The picture in Fig. 50 shows the XMOTR truck beneath a powerline in the Camp Oharles Wood Motor Pool yard, 1400 fee+. east of the Hexagonbuilding, i.e., at location 1 in the mAap in Fig. 51. During the first teston 29 Jan. 1973, signals transmitted on 85.2 kHz from the XMTR-truck locatedunder the power line in the Charles Wood Motor Pool area were received sostrongly by the LF-VLF station in the Hexagon, that the crimary )XTR powerhad to be reduced to approximately 30 watts. The transmissions were continuedat the lower power level until 31 Jan. 1973. Until 0930 hours local tine.of this day, the 82.5 kHz emission as received, recorded bl the IF-VLFstation in the Hexagon building, was essentially stable. After 0930 hours,strong amplitude fluctuations set in with periods of approximately fiveminutes. The tr&,ismissions were then terminated at 1600 hours since noapparent reason for these fluctuations could be found and because of possiblerisks of continuing the transmissions unattended over the holidays. Thetransmission tests were resumed on 8 Feb. under stable conditions. On12 Feb., at about 10O0 local time (1900 GMT), the XMTR was disconnectedfrom the commercial AC power supply and switched to a gasoline driven AC Sgenerator. Subsequently, the XMTR truck was moved from the motor poollocation to ECOM's new "Green-Acres" office building on the western side ofthe Garden State Parkway and about ½ mile west from the Hexagon building.

On the way to the Green Acres bui2ding, an intermediate stop-over was made on the parking lot north of the Hexagon, approximately 300 feet

57

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0

4d'II

,Jul

Ihis pagea Is reproducod at theFig. 48 LF - mTR Solenoid on M-1.09 biick of the report by a differentTrulck Roof Ueroductio, method to provide

tte detal,

58

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- Fig. 5'1 Map - Hoxagon LF-V7iY Re eiverStation and Lr-WrP TrujckEoCfitions #2 ana #2(8 5.2 kHz Tranwnission Tesut)

61 12 Feb. 1973

dL Aft ALo

from the north side wall of the Hexagon, at location 2 in the map in Fig. 51. • 1In contrast to the MTR truck position at the Hexagon, a special effort wasmade at the Green Acres building to park the WrTR trick within approximately10 feet di3tan-e from the aluminum panel walls of the building such thatthe XMTR solenoid was parallel to the walls. At the Green Acres site, thetruck was first positioned on the south side of the building's wing whichprojects towards the east. Then the WMTR truck was positioned at thenorthern side of the Green Acres building, such that the building blockedthe line-of-sight path towards the Hexagon. This position of the XMTR truck bis shown In the picture in Fig. 52. CW signal transmissions from these foui'locations, at the motor pool, on the north parking lot of the Hexagon and onthe south and north side walls of the Green Acres building were received viahorizontal wire antenna on the Hexagon roof and recorded at the HexagonLF-VLF Station. The received 82.5 kHz signal levels, as functions of time(am?), and corresponding XMTR locations are shown in Fig. 53. Comparingthe reoeived signal levels and the corresponding transmitter to receiverdistances involved, it is evident that the metal structure of the Green Acresbuilding enhanced radiation of the LF signal stronger than the overhead powerline at the motor pool location; variations of signal level, during the timeof transmission from the respective XMTR locations, are largely due to theAC drift of AC primary power output from the gasoline driven AC generator.

Further evidence of the support role for LF comununicatione ofurban media is shown in Figs. -. and 55. Here IF signals are received withan HRO-50O National Radio Receiver using ferrite loopsticke to pick up thesesignals from a water fountain and a heating radiator inside the Hexagonbuilding. In contrast to the previously discussed transmissions on the XTAL *controlled frequency of 85.2 kHz, the exact transmission frequencies werein these Nov. 72 tests dependent on the location of the XMTR truck and onits proximity to urban structures in its immediate environment, such as thewater tower on the southeastern side of the Hexagon building, the supportframe of the truck entrance and the yard-side walls of the Hexagon building(Map Fig. 51). At these locations the transmitted 80 to 90 kHz signalfrequencies were generated by regenerative feedback obtained by connectingthe output from the ferrite loopstick probe inside the track (Fig. 49)to the input of the power amplifier circuit that feeds the XMTR solenoid onthe roof of the truck (Fig. 48). Conssquently, the EM coupling to adjacentsecondary structures and the corresponding loading of the regenerative feed-back circuit influences its frequency of oscillation. Observed frequencychanges due to loading by "secondary structures" indicated that the couplingis r.ot efficient, but results of the transmission experiments prove thatthe coupling is sufficient to pollute the Hexagon and parts of the adjacentBuilding 2525 by LF signals which are much stronger than the RF pollutionfrom other sources including, in one case, an LF transmitter station of theUS Navy.

3. SUMMARY AND CONCLUSION S

A. Employing a phased twin tree array control over the directivity ofHEMAC induced RF (4.650 MHz) radiation from large forest trees has beentaken from the natural forest tree configurations and handed to the radiooperator. 5

62

J&

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J101

r.i p.r-e

bahk op ge Isreport bye at dfenthFig. 52 LF-DI'TR Truack at Green Acres epouction method to provide

Office Building (85.2 kHz bette detail.Transmission Test) 1 e.17

63

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ouotion method to providebetter detail.

66

A

B. The previously. observed abrupt deoay of radiation from differenttreessat frequenoiessbetween 7&M 11 H~s were found to berelated to theocouirenos of several resonamce. In the tree loaded HUIAC circuit.

0. Pursuing further the determination of practical upper frequency (limits for the operation of trees as antennas, radiation measurements weremade at frequeneies between 5.5 MOz and 11.0 MIs.

In these measurements man-planted smaller shade trees and theirnaighboring urban jungle counterparts, i.e., metal lantern poles of comparableheightwre put to work as HF radio antennas.

In ground to ground transmissions over 7 miles employing the PRC-74radio transoeiver and various smaller HMAC'I, the lantern poles outperformedthe PRO-74 whip by 2 to 12 dB and the HEDA&'e by themselves bý 10 to 18 dB.The shade trees and the PRO-74 whip performed about equally well, with thetree yielding slightly better signal to noise ratios most, of the time.Suspecting related differences in the ground and sky wave emission patterns,measurements were made of the RF output voltages from a HEMAC coupled lanternpole, a small shade tree, and the PRO-74 whip which were immersed into theRF field from an 8.25 Me XTAL controlled test transmitter mounted in agondola of an aerial tramway suspended above the respective receiver antennas,The recorded sharp null in the lantern pole output in contrast to the broadmaximum of the tree output when the XMR gondola moves over respectivelythe pole and the tree, indicate oorresponding differences in their radiationpatterns. Accordingly, ground and sk7wave emission seem to dominate RFradiation from the lantern pole and the tree. However, the actual spatialdistribution of radiated sky and ground wave modes must be determined by S Sradiation field pattern measurements by airplane. This is particularlytrue for the twin HDMAC coupled lantern pole case where a parasitic IEACcircuit is used similarly as the center coil resonator of the PRO-74 whipto influence the RF current distribution along the lantern pole and thusits relative ground and sky wave emission ability.

1). The introduction of metal lantern poles as performance standardsfor trees of comparable height at higher frequencies opens the way for theexploitation of diverse structures and materials or urban jungles asantennas and RF transmission media.

The roles of buildings for these purposes were established at HF 0and LF frequencies. Between 8 and 12 MHz, evidence of the superior radiationabilities of HEMAC coupled metal window frames relative to a resonant dipolemounted across the window panes of the Hexagon building, was established bymeasurements at a fixed station 7 miles to the south wid by communicationrange tests east and west from the Hexagon.

The resultant communications ranges 3.5 miles east and 8.5 mileswest reveal the influence of the buildings' geometry on the directivity ofHF radiation. Such directional phenomena were not. observed in the diffusionof 82.5 kHz signals from ECOM's new Green Acres building to the Hexagonbuilding and in the pollution of the water distribution system of the Hexagon

67

- • • . . . ' • • . .. . . . '- .-' • . . . . .. .. .' i . . . .. . . . • ' .. . . . .. .. .. • .. . .. " . • •I

building with LF signals in the 70-90 kHz range. Hocwever, the LF diffusion .and posesbly secondary radiation enhancing role of buildings, has becomeevident as a result of these LF transmission experiments.

4. RECOMMENDATIONS

A. Incorporate into the planned measurements, by airplane, of the skywave radiation from forest trees corresponding pattern measurements of theradiation from the lantern poles and from the window frame.

B. Perfect the method of coupling of RF power to and from structuresand materials of urban jungles for their use as efficient and camouflagedradio antennae and transmission media.

C. Investigate the feasibility of clandestine communications in urbanjungles by exploiting their RF pollution by friend or foe as transmissioncorrelation references.

D. Apply the HEMAC methods and techniques to the exploitation of the

super structures and the hulls of ships and planes as LF, MF and HF antennas.

5. ACKnonZo TS

Research and development, leading to the expluitation as radio antennasof live vegetation in natural jungle environments, have been guided initiallyby Col. J. P. Dobbins during his tour of Duty as Director of 3COM'. souiunn- C 0cations/ADP Laboratory.

Col. J. D. Mitchell, the present Director of the Laboratory, in pro-viding overall guidance and special technical advice for the applicationof HERAC techniques to the exploitation as RY antennas and transmission mediaof diverse structures in man made urban jungle environments. p

Mr. Richard Simmons, from SOOM's OSTA Laboratory, has assisted in thevarious transmis.ion measurements from the Wayside and Hexagon areas to theSvans area radio station.

Mr. James Hargrave and SP5 Gerald D. Cook received and recorded at theHexagon LP-VLF station the LF signal emissions from various locations inthe Camp Charles Wood, Hexagon area, and the Green Acre's area.

6..,EERcS

1. George 0. Squire, "Tree Telephony and Telegraphy," the "rknklinInstitute Journal, Jime 1919.

2. U. S. Patent #3646562, March 72.

3. "Performance of Trees as Radio Antennae in Tropical Jungle Forests(Panama Canal Zone fteriments)," RTR-ECOM-3534 (AD 7I42-230),Feb 1972. p

68

S! , " i ' '• .' : .

4, "Signal Propagatior% at 400 k.• Using an Oak Tree with a HS(AC anAntenna," RDTR-MoO-3504 (AD 735-330), Nov. 71.

5. "Ixploitation and Performance of Forest Trees as Antennas forRadio Oommunoations in Dense Forest Covered Terrains (Synopois ]of Lebanon State Forest N.J. Experiments)," RDTR-BCOM-3508(AD 737 308), Nov. 71.

6. "Devlopment of Camouflaged Body Ooupled Radio Transmitters,"RDR-ECH-4.0I4, April 1973.

7. "Use of Railroad Tracks for Carrier Telephony and as Long WireAntennas for Transmission of Long Wave Radio Signals," RDTR-ECOM-2816(AD 822 4i78), Julyv 1967.

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NATURAL AND IN MAN WADE JU•NLES

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Natural forest trees, man-planted shade trees, metal lantern poles andbuilding structures were utilized as efficient HF radio antennas with theaid of Hybrid Electromainetio Antenni Couplers (HEMAC's). The performanceof live tress and of inanimate metal structures ap antennas is comparedwith the performance of conventional HF whip and dipole antennas. Similarpractical data are given on the LF radio signal emission capabilities ofhuge steel-concrete buildings and on LN radio signal diffusion via electricalpower and water distribution nystems in suburban areas.

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