Moonbounce Communication Report

8/12/2019 Moonbounce Communication Report

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ABSTRACT

Microwave engineers and engineers in general tend to be in their profession because they like

technical challenges. Historically, one of the biggest challenges has been how to extend radio

communications, especially at microwave frequencies, beyond the horizon. One way to

achieve this end at microwaves is to bounce radio signals off the Moon. This form of

propagation is known as Moonbounce or Earth-Moon-Earth (EME) and is considered the

ultimate in long-distance 50-MHz-and-above communications. The Moon is approximately

385,000 km (240,000 mi) from the Earth, and reflecting signals from it allows

communication between any two points. Since the Moon is so far away and not a particularly

good reflector (about 7% efficient), communication using it as a passive reflector is not easy

and considered by many a challenge. This report will discuss EME in more detail. It will

cover some of the history of this form of propagation, challenges faced in communication, the

necessary system design required to obtain optimum result and the present scenario.


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CONTENTS

TITLE PAGE NO.

Chapter 1: Introduction

1.1 General Background 1

1.2 Objective and Scope of the work 3

Chapter 2: Challenges in Reaching the Moon 5

2.1. Distance between Earth and Moon 5

2.2. Path Loss 5

2.3. Natural and Man Made Noise 8

Chapter 3: EME System Considerations 10

Chapter 4: System Design 13

4.1. Transmitter 13

4.2. Antenna 14

4.3. Receiver 17

Chapter 5: Digital Signal Processing In Moon bounce 19

5.1. Communication via Jt65 20

5.2. Present Scenario 22

Chapter 6: Conclusion 23

References 24


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CHAPTER 1

INTRODUCTION

1.1 GENERAL BACKGROUNDDuring World War II, there were reports of possible reflections of radar

signals from the Moon. It was not until after the war, in 1946, that the reflection of radio

waves off the Moon was documented. A group of U.S. Signal Corps engineers achieved the

honour of detecting the first documented radio signals reflected from the Moon as part of a

project called Diana. This project was the brain child of John DeWitt, a fellow of the Institute

of Radio Engineers (IRE) (predecessor to the IEEE), a radio amateur (N4CBC) and the

project leader. The experiment was conducted at 112 MHz, using what we would call today a

large phased array and a 3,000 W transmitter built by Edwin Armstrong as shown in fig 2.1.

Fig 1.1.Phased Array Fig 1.2.Zoltan Bays technique

At almost the same time, Zoltan Bay, working in Hungary, achieved

similar results. He used the same frequency range and a similar antenna, but, because of


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transmit power limitations, he developed an ingenious technique to detect the reflected

signals. He sent repeated pulses over an extended period of time (months) and integrated the

returned signals. Each time he sent a pulse, he would detect the signal over the expected echo

time period and sum/store the voltage received at each point in time (see Figure 2.2). Because

he lacked a way to retain voltage over a long time (capacitors were leaky), he applied a

technique from chemistry. He used the detected voltage for a hydrolysis of water, converting

the water into hydrogen and oxygen gas. After many transmissions, he analyzed the amount

of gas produced, which he stored in jars associated with different intervals of time. He found

the jars corresponding to 2.5 s after transmission of a pulse, the time for a signal to travel to

the Moon and back, contained by far the most gas.

The concept of using the Moon for radio communications actually preceded

the Diana experiment. W.J. Bray of the British General Post Office proposed the idea in

1940. Not long after the success of Project Diana, the military started to employ the Moon for

long-distance microwave communications that were free of the vagaries of ionosphere

propagation seen at lower frequencies. These applications of moonbounce included a teletype

link between the naval base at Pearl Harbour, Hawaii and the U.S. Navy headquarters in

Washington, D.C. Eventually, these links were replaced by active communication satellites.

Another group that saw the potential of moonbounce was the radio amateur community.

Many radio amateurs are involved in the hobby because they are interested in technical

challenges and in extending the limits of radio propagation. They compete to see who can

consistently communicate the farthest at the highest frequency. Moonbounce offered a way to

achieve communication over distances not possible by other means. Amateurs were not far

behind the professionals. In January 1953, Ross Bateman and Bill Smith reported reception

of EME echoes on 144 MHz but never achieved two-way communication. It was not until


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1960 that the first two-way contacts were made at 1,296 MHz by a group led by Sam Harris

and amateurs from the EIMAC Radio Club led by Bob Sutherland. Within a year, two-way

contacts were completed on the 432 MHz and 144 MHz bands. Sam Harris later became chief

engineer of the 305 m (1,000 ft) Arecibo Radio Telescope. By 1973, the use of EME by

amateurs had increased to the point that communication at 432 MHz could be completed with

all continents by one of the authors, Allen Katz. Today, EME contacts have been made on all

the amateur bands from 28 MHz to 47 GHz with countries all over the Earth.

1.2OBJECTIVE AND SCOPE OF THE WORKMoonbounce or (EME) Earth-Moon-Earth form of propagation is a form of radio

communication technique which is used to extend the communication beyond the horizon.

Humans have been using the link of satellites for communication for decades. One of the

main disadvantages of using such a system is the escalating cost of manufacturing a satellite

and then placing it in the orbit. Various categories of satellites are there based on their

positions. Also the cost of maintaining a satellite for such a long period is very high. But,

humans have forgotten the fact that we already have a natural satellite in moon and have not

yet been to discover the tremendous possibilities using moon for a communication. Space is

also getting polluted with the remains of these satellites.

Moonbounce is a technique used to find a solution to all these problems. In

moonbounce communication, signals are sent to the moon and are reflected back from the

lunar surface. Microwave frequencies of over 100MHz are used for communication as very

high power is required so that signal reaches the moon after suffering so much loss. Higher

the signal power and frequency a much better signal can be detected. The only investment

one needs to look into while establishing such a communication system is on a high power


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transmitter, a good antenna and a receiver. Compared to hundreds of crores of rupees spent in

constructing a satellite, it is a good gain.

Because of the distance between earth and moon, this form of communication is seen by

many as a challenge. But it is one of the most popular forms of communication beyond

50MHz. But till now only radio amateurs are the only group utilizing this communication

technique and seeing it as a challenge. The effort is to raise the maximum frequencies so that

losses are minimized. Research is going on in popularizing this form of communication and

in a few years time, EME or Moonbounce is going to be the Ultimate word in long distance

communication.


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CHAPTER 2

CHALLENGES IN REACHING THE MOON

Before establishing a communication link between earth and moon, one needs

to look into the challenges to be faced to establish such a communication system. Many

aspects should be taken into consideration to design a very efficient system since the distance

is very large and huge losses are bound to occur.

The main challenges are:

2.1DISTANCE BETWEEN EARTH AND MOONThe Moon is approximately 385,000 km (240,000 mi) from the

Earth, and reflecting signals from it allows communication between any two points. Because

the Moon is so far away and not a particularly good reflector (about 7% efficient) ,

communication using it as a passive reflector is not easy and considered by many a challenge.

2.2PATH LOSSRadio signals in free space are attenuated as 1/r2(inverse distance squared)

due to spatial expansion of the radio waves. In moonbounce, this dissolution of signal

intensity occurs twice; first, over the quarter-million-mile path to the Moon and again on the

return trip, for a net 1/r4path loss. Radio waves hitting the surface of the Moon are partly

absorbed and partly scattered by the irregular surface. The EME path loss, L, as a ratio of

received power to transmitted power in decibels, assuming isotropic antennas at each end,

can be expressed as (figure 2.1).


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where d is the diameter of the Moon, l the wave-length, r the distance to the Moon,

and h a factor for lunar reflection efficiency. Using d=53.476 x 106m, r=53.8 x 108m, and

h=50.07 gives an L of 251.5 dB at 144 MHz, currently the most popular amateur band for use

of EME, and nearly 300 dB for 47 GHz, the highest frequency band where amateurs have

achieved EME so far.

Fig 2.1.Mean Path Loss to the moon and back


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These very large values of loss are the main

reason why EME is so challenging. The signal level difference between receiving a signal

transmitted from the Moon and one reflected from it is enormous. For the example cited, it is

almost 130 dB. It is thus much easier to receive a signal transmitted from the Moon. Many

radio amateurs monitored the signals transmitted by astronauts during the Apollo missions.

The values above are for the average L. The Moons orbit is an ellipse, causing r to vary by

about 67% each month with a corresponding variation in L of nearly 2.25 dB [12] ,[13]. The

dependence of L makes it appear that EME is more difficult at higher frequencies (figure

2.2). This conclusion is misleading because the assumption is based on the use of isotropic

antennas.

Fig 2.2.Path loss at different frequencies


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2.3 NATURAL AND MANMADE NOISE

The terrestrial environment is continuously exposed to electromagnetic radiations which set

up a background electromagnetic noise.For what concerns electromagnetic waves in the

Non Ionizing Radiation band (NIR), i.e. for frequencies lower than 300GHz, the background

can have a natural or artificial origin. In the first case electromagnetic radiations have

generally an atmospheric or cosmic origin while in second case human technologies,

implanted for power transmission and communications, are the non natural cause (Figure

2.3).The terrestrial environment is continuously exposed to electromagnetic radiations whichset up a background electromagnetic noise. Within the Non Ionizing Radiation band (NIR)

i.e. for frequencies lower than 300 GHz, this background can have a natural or an artificial

origin.

Natural origins of electromagnetic radiations are generally

atmospheric or cosmic while artificial origins are technological applications, power

transmission, communications, etc. Natural noise comes from a large variety of sources

involving different physical phenomena and covering a wide range of frequencies and

showing various propagation characteristics with an extremely broad range of power levels.

Due to technological growth man-made electromagnetic noise is nowadays superimposed on

natural noise almost everywhere on Earth. In the last decades man-made noise has increased

dramatically over and above the natural noise in residential and business areas. This increase

has led some scientists to consider possible negative effects of electromagnetic waves on

human life and living systems in general. Accurate measurements of natural and man-made

electromagnetic noise are necessary to understand the relative power levels in the different

bands and their influence on life.


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Fig 2.3.Natural and Manmade noise sources


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CHAPTER 3

EME SYSTEM CONSIDERATIONS

An EME communication system basically consists of a transmitter, antennas

(used for both transmit and receive), and a receiver. The modulation used is also an important

factor in of the overall system performance. The signal power received, Pr, is simply the

transmitted power, Pt, times the gain of the transmit antenna, Gt, times L, times the gain of

the receive antenna, Gr. Noise is contributed by the receiver and the antenna and ultimately

set the limits on the ability to communicate. Noise from the antenna includes contributions

from the warm Earth, the atmosphere, the lunar surface, and cosmic sources. It is often

convenient to express noise power in terms of an equivalent noise temperature, T.

T is related to power, P, by the receiver bandwidth, B in Hz, and Boltzmanns constant, k

51.38 3 10223 J/K:

The system noise temperature, Ts, is

Where, Tr is the receiver noise temperature and Ta is the antenna noise temperature. Tr is

related to receiver noise figure, NF in dB by


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Ta includes noise from all sources in the field of view of the antenna, weighted by the

antennas pattern. The lunar surface has a temperature of around 210 K but has a minimal

contribution to Ta since most amateur antennas have beam widths much greater than the

Moons angular size. Antenna sidelobes can be a s ignificant contributor to Ta because their

total solid angle can be large, and these sidelobes need to be considered even if they are many

decibels down from the main beam. Below 1 GHz, the most important antenna noise source

is cosmic noise, primarily from our galaxy. Cosmic noise scales with frequency to a 2.6

power, as illustrated in Figure 3.1.

Figure 3.1.Noise temperature for a typical antenna

This figure assumes a typical amateur EME antenna, one designed

for the addition of low Earth noise. At VHF, Ta can increase by as much as ten times in


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average value depending on the location of the Moon in the sky at different times of the

month. For frequencies 1 GHz cosmic noise is negligible in most directions and can be

virtually ignored. At frequencies greater than about 5 GHz, the Earths atmosphere starts to

contribute to Ta, and noise power increases again. Because of the huge path loss, EME

signals are normally weak, and achieving a positive signal-to-noise ratio (SNR) is of

overriding importance. If Pnis the total noise power, SNR can be expressed in dB as:

Radio amateurs are usually not interested in transmit-ting large amounts of information; their

main goal is establishing communication under very weak signal conditions. EME

transmission bandwidth requirements are thus normally small, and a minimum bandwidth is

often used, (as little as one hertz, or even less), to maximize the SNR.


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CHAPTER4

SYSTEM DESIGN

4.1 TRANSMITTER

The focus of transmitters used for EME is on the power amplifier. Generally, the

highest power is desired to maximize the SNR. This power level is limited by regulations,

available technology, and economics. The maximum output power in the United States is 1.5

kW, but many stations run lower power. At frequencies below 2 GHz, gridded vacuum tube

power amplifiers still dominate, but are rapidly being replaced by solid-state power

amplifiers (SSPAs), particularly at lower power levels (less than 100 W). A block diagram of

a typical VHF amateur transmitter is shown in Figure 4.1. At frequencies above 2 GHz,

travelling wave tube amplifiers (TWTAs) dominate but are also being rapidly replaced by

SSPAs. The transition to SSPAs is the principal advance in transmitter technology since the

early period of EME when a 3-kW transmitter was used for the first echoes. Examples of an

SSPA and TWTAs are also shown in Figure 4.1.


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Figure 4.1.EME transmitter and solid-state power amplifier

4.2 ANTENNA

Many amateurs consider the antenna the most important component of an

EME station and devote a large share of their effort on it. There are essentially only two types

of antennas used by amateurs for EME today: the yagi and the parabolic dish, although there

are many variants of these basic antennas. Yagis, either singularly (usually very long in

wavelengths) or in arrays, are used almost exclusively in VHF bands.

Figure 4.2.Large yagi array Figure 4.3.Single yagi antenna


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Figures 5.2.1 and 5.2.2 show examples of a large yagi array and a single yagi

antenna, respectively. Both linear and loop element yagis are used. At higher frequencies,

parabolic dishes dominate and are used almost exclusively above 2 GHz. Both full and offset

dishes are used, with offset designs more common at frequencies above 5 GHz.

Figure 5.2.3 shows a 15-m dish used for EME by HB9Q in Switzerland.

Considerable effort by many individuals has been applied to the design of high-gain yagis

with special attention paid to achieving minimal sidelobes to keep Ta low. This effort has

been made possible by the availability of accurate antenna modelling software. The gain of a

modern, well designed yagi of length l can be approximated by the equation G=58.1 log1l/l2

111.4 dB.

.

Figure 4.4.EME 15m dish used by HB9Q


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Yagis are light, relatively easy to build, and have low wind resistance. Long yagis

designed for EME are generally narrowband antennas with bandwidth traded for gain and

better sidelobe performance. Yagis can be combined in phased arrays to yield nearly 3 dB for

each doubling of the number of elements. Large arrays of eight, 16, or even more yagis are

not uncommon. The gain of a parabolic dish of diameter d with a feed yielding 55%

efficiency is G=520 log1d/l2 17.3 dB.

The gain of many of the dishes used for EME is probably somewhat higher

than given as considerable time has also been spent modelling feed designs for optimum

efficiency. A popular method of constructing dishes by amateurs is to make use of the natural

tendency of materials to form an approximate parabolic shape. Dish antennas offer the

advantage of being usable on multiple frequency bands by simply changing their feed

antenna or using a multiband feed. A linear polarized antenna is usually thought of as being

either horizontal or vertical. When dealing with the spherical Earth, these concepts have

meaning only locally. As seen from the Moon, horizontal antennas on different continents

will have very different orientations. In addition, when a linearly polarized wave passes

through the Earths atmosphere, its plane of polarization is rotated in proportion to the local

free-electron density, the Earths magnetic field intensity, and the square of wavelength. This

phenomenon is known as Faraday rotation. Faraday rotation is greatest during the daytime for

stations well away from the equator and at low (VHF) frequencies. A mismatch in angle, DU,

between an incoming waves polarization and the receiving antenna will attenuate the

received signal power by cos2DU. Polarization losses increase to 3 dB when the

misalignment is 458 and increase rapidly at high angles up to 908. Because of the l2

dependence, Faraday rotation is only important for EME operation below 1 GHz, and is

insignificant at higher frequencies. Faraday rotation in the daytime ionosphere can be as

much as a full turn at 432 MHz and many turns at 144 MHz. At 432 MHz, the rotation may


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made the Ga-As low-noise preamplifier (LNA) an integral part of virtually all amateur EME

stations. Amateurs have become adept at producing LNAs that rival the best professionally

produced amplifiers [15]. At 1,296 MHz, LNAs with a Tr under 10 K have been reported (see

Figure 5.3.2) and, even at 78 GHz, low-noise receivers have been produced by amateurs for

EME, as shown in Figure 5.3.3.

Figure 4.6.Very low noise amplifier Figure 4.7.Low noise 78GHz receiver

Any feed-line between an antenna and a receiver introduces attenuation and

noise. Consequently, LNAs for EME are normally mounted as close to the antenna terminals

as feasible to achieve the lowest possible noise figure. At ambient temperature, every 0.1 dB

of loss in front of the LNA adds about 7 K to Ts. At microwave frequencies where antenna

temperatures are much lower than ambient, this change can correspond to a receiver

degradation of more than 0.5 dB. LNA gain must be sufficient to overcome subsequent feed-

line losses and dominate the noise contributed by subsequent stages. Since the same antenna

is generally used for both transmit and receive, the LNA must be switched out of the line

when transmitting, and thus the transmit/receive relay used must also be selected for

minimum loss.


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Figure 5.1.Libration fading effect variation with frequency and position

The success of the new digital modulation formats/DSP techniques that have become

popular in recent years is based on eliminating the need to accurately know and maintain a

stations frequency. In the past, it was essential to very accurately know the frequency to find

and decode a weak signal utilizing effective minimum bandwidths that could be a few hertz

or less; a technical requirement not easily accomplished by many radio amateurs.

5.1 COMMUNICATION VIA JT65

The digital modulation most widely used for EME is JT65 [19], [20]. This mode was

conceived by Joe Taylor (K1JT), a Nobel Prize winning physicist. It employs a synchronizing

(sync) signal with a quasi-random amplitude pattern to provide both frequency and timing

information (see Figure 7.1).


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dashes. Consequently, JT65 can be sent more slowly than CW and be detected in a smaller

bandwidth (5 Hz for the JT65B mode used on 144 MHz versus about 50 Hz for CW). CW is

self-synchronizing at the character level (if strong enough for letters to be recognized), but

provides no means for synchronizing a whole message, which makes piecing together

fragments of a repeated CW message difficult. JT65s Reed-Solomon block coding enables a

full message to be decoded with no errors with high likelihood even when less than a quarter

of the symbols have been correctly copied.

5.2. PRESENT SCENARIO

.

At the time of this writing, use of EME is highest in the 144 MHz band,

where JT65 is by far the preferred modulation. Just about any time the Moon is above the

horizon in Europe and North America, JT65 EME signals can be detected in the frequency

range between 144.100 and 144.160 MHz. Several hundreds of stations worldwide regularly

operate with moonbounce using JT65 on 144 MHz. The next two most popular EME bands

are 432 MHz and 1,296 MHz. In both these bands there is still significant use of CW and

even SSB (voice) modulation for EME communications because of the higher SNRs that can

be achieved with moderate sized antennas. Use of digital modulation techniques is growing in

these frequency bands as new radio amateurs in many countries are no longer required to

know CW. A hundred or more stations are typically active on these bands during regularly

scheduled international EME competitions, and in other major operating events. The higher

microwave bands, 2.3 GHz and above, have at least several dozen stations that regularly

operate EME.


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CHAPTER 6

CONCLUSION

Most of the amateurs involved in EME do it for the technical challenge. The thrill of building

a system with which one can send a signal into space and detect signals returning from the

Moon is very real. Many of the amateurs involved in EME are also interested in extending

the state of the art of radio communications. Improving antenna and receiver performance has

always been a major component of EME, now DSP and the search for improved algorithms

for the reception of weak signals from the Moon is also a part of it. The effort to extend the

highest EME frequency, presently to 78 GHz goes on....and the quest continues.


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8. REFERENCES

[1]. Allen Katz and Marc Franco, (2011)Targeting the Moon, IEEE microwave

magazine. 5thMay 2011.

[2] J. H. Dewitt, Jr. and E. K. Stodola,(1949) Detection of radio signals reflected from the

moon,Proc. IRE, vol. 37, no. 3, pp. 229242, 1949.

[3] H. Kauffman,(1946) A DX record: To the moon and back, QST, vol. 30,pp. 6568,

May 1946.

[4] D. D. Grieg, S. Metzger, and R. Waer,(1948) Considerations of moonrelay

communication,Proc. IRE, vol. 36, no. 5, pp. 652663, 1948.

[5] Z. Bay,(1946) Reflection of microwaves from the moon,Hungarica Acta Phys., vol. 1,

no. 1, pp. 122, Apr. 1946.

[6] J. Pether, (1998)The Post Office at War. Bletchley Park, Milton Keynes: Bletchley Park

Trust, 1998, p. 25.

[7] M. A. Weston,(1968) Microwave moon relay communication at high digit rates,Proc.

Inst. Elect. Eng., vol. 115, no. 5, pp. 642651, 1968.

[8] R. Bateman and W. Smith, (1953)Lunar DX on 144 Mc, QST,vol. 37, pp 1112 and

116, Mar. 1953.

[9] Coast to coast via the moon on 1296 Mc, QST, vol. 44, pp 1011, Sept. 1960.

[10] J. M. Morris, (1976)K2UYHMoon bounce WAC, QST, vol. 60, pp. 5760, Sept.

1976.

[11] A. Ward and B. Malowanchuk,(2008) 24 and 47 GHz EME, inProc. 2008

EME Conf., Florence, Italy.

[12] ARRL Hand Book for Radio Communications, 2010, 87th ed. EME.

[13] J. V. Evans, (1995)Radio communication via the moon, inProc. Int. Conf. 100 Years

of Radio, 1995, pp. 207212.

[14] D. Mc. Arthur, The VK3UM radiation and system performance calculator [Online].

Available: http://www.qsl.net/sm2cew/VK3UM_RPC_431, Mar. 2011.

[15] S. Zhutyaev. 1296 MHz small EME station with good capability (part 4) LNA

optimization[Online]Available:http://www.vhfdx.ru/apparatura/rw3bp_1296mhz_lna_optimi

zation, Mar. 2011.


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[16] P. Wade. W1GHZ VE4MA and chaparral feeds with septum polarizers [Online].

Available: www.w1ghz.org/antbook/conf/VE4MA_Chaparral_septum_feeds.pdf, Mar. 2011.

[17] K2UYH. 432 and above. [Online]. Available: www.nitehawk.com/rasmit/em70cm.html,

Mar. 2011.

[18] M. Franco,(2008) Computer optimized dual mode circularly polarized feedhorn, in

Proc.2008 EME Conf., Florence, Italy.

[19] J. Taylor,(2005) The JT65 communications protocol, QEX, Issue 232, pp. 312,

Sept.Oct. 2005.

[20] K1JT. WSJT homepage [Online]. http://www.physics.princeton.edu/pulsar/K1JT/, Mar.

2011.

[21] F. J. Kerr and C. A. Shain,(1951) Moon echoes and transmission through the

ionosphere,Proc.IRE, vol. 39, no. 3, pp. 230242, 1951.

[22] T. Senior, K. Siegel, and H. Weil,(1958) The influence of radar reflection

characteristics of the moon on specifications for earth-moon-earth communication systems,

in WESCON/58 Conf. Rec., 1958, vol. 2, part 1, pp. 197201.

[23] B. S. Yaplee, R. H. Bruton, K. J. Craig, and N. G. Roman, (1958)Radar echoes from

the moon at a wavelength of 10 cm,Proc. IRE, vol. 46, no. 1, pp. 293297, 1958.

[24] P. A. Webster, (1961)Long distance communication via the moon,J. Br. Inst. Radio

Eng., vol. 22, no. 3, pp. 257264, 1961.

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Moonbounce Communication Report