8. HIGHER FREQUENCY TECHNIQUES, Departments of the Army and Air Force, 1952
9. IEEE AEROSPACE and ELECTRONIC SYSTEM MAGAZINE Vol.3 No.12, DEC. 1988
Copyrights by respective organizations and Ideas Unlimited, Corp.
Radiation from deep space detection PART 1 Radiation through space and back PART 2
We will recreate these New Jersey first into the present in such a way that you will understand how these science pioneers handled basic communication and space principles with hard work, determination and ingenuity.
We will use decimal units as used in common practice.
RADIO and RADAR Radio Detection And Ranging
Basic foundation originated in Europe
Michael Faraday (1791-1867) Electric magnetic field around a conductor James Clerk Maxwell (1831-1879) Mathematical model for electromagnetic waves propagation Heinrich Hertz ( 1857-1894) Demonstrated the existence of electromagnetic waves Guglielmo Marconi (1874-1937) Built wireless apparatus and Patented in England
US patents for elementary wireless apparatus has been granted to a number of researchers such as: Thomas A. Edison (1891) ; Oliver Joseph Lodge (1894); Nikola Tesla (1897) Worked at Edison Power Station then Joined Westinghouse and then started his own company.
US Supreme Court overturned Marconi’s patent and in 1943 credited Tesla with the invention of Radio.
However Marconi excel as businessman and soon became a world radio communication monopoly with Marconi’s Wireless Telegraph Company. Made demonstration to the British and US Navy and Transoceanic communication.
Initial wireless technology used the spark gap principle before Hertz to Tesla, Marconi and others.
The history of radio shows that the spark gap transmitter was the product of many people, often working in competition. Battery energy was transferred to a coil and a capacitor as a spark jumped the space oscillates and discharged into an antenna that irradiates a radio signal.
Propagation through free space occurs at a velocity of nearly 300,000 km/sec.
f is the frequency of oscillation in Hz/sec.
c the velocity of propagation of electromagnetic radiation in m/sec.
Then we have: c= f λ or λ m)=300/f(MHz)
Electrical wave generation
The capacitor is fully charged and there is no current passing through the coil. This situation is unstable and the capacitor spontaneously discharges via the coil, creating a current in it which is linked with a magnetic field. The energy stored in the capacitor (potential energy) is exchanged for the energy associated with the magnetic field and flowing current (kinetic energy) in the coil. In other words, the capacitor is the generator, and the coil is the load.
The current flowing in the coil is at a maximum and so is the associated magnetic field. The capacitor is fully discharged. Unfortunately, because of this, at this very moment the power supply fails. The situation is unstable. The current flow ceases momentarily, the magnetic field gradually collapses, and a current is induced in the coil, passes out of the coil and charges up the capacitor. Kinetic energy is exchanged for potential energy, the above formula is effectively written the other way around,
now the coil has become the generator and the capacitor has become the load.
Since the impedances of coil and capacitor are conjugate, the maximum power is transferred from (transferred from, not consumed by!) one to the other at the condition of resonance.
If there was no resistance in the circuit, this exchange or oscillation would continue indefinitely because the current and voltage are out of phase in each branch of the circuit and no power is consumed; the damping and decrement would be zero and the Q infinite. Some how this circuit deliver the oscillation and a Power Supply sustain the oscillation.
If the resistance in a tuned circuit is negligible, then the resonant frequency is given by the well-known formula: f=1/2Pi Square root LC
RADAR Astronomy active observation
Radar astronomy is a technique of observing nearby astronomical objects by reflecting microwaves off target objects and analyzing the echoes. This research has been conducted for four decades. Radar astronomy differs from radio astronomy in that the latter is a passive observation and the former an active one. Radar systems have been used for a wide range of solar system studies. The radar transmission may either be pulsed or continuous.
The strength of the radar return signal is proportional to the inverse fourth-power of the distance. Upgraded facilities, increased transceiver power, and improved apparatus have increased observational opportunities.
Lt. Col. John H. DeWitt, Signal Corps Evans Signal Laboratory Director. W4ERI
Born in Nashville, attended Vanderbilt University Engineering School for two years. Vanderbilt did not offer electrical engineering, so DeWitt dropped out in order to satisfy his interest in broadcasting and amateur radio.
After building Nashville's first broadcasting station, in 1929 DeWitt joined the Bell Labs NY City, designing radio broadcasting transmitters.He returned to Nashville in 1932 as Chief Engineer of radio station WSM.
State of the art and Project
“Radar was developed by men who were familiar with the ionospheric work. using widely-known scientific technique, which explains why the development of radar--took place simultaneously in several different countries."
In September 1945, DeWitt assembled his team:
Dr. Harold D. Webb, Herbert P. Kauffman,
E. King Stodola, and Jack Mofenson.
Dr. Walter S. McAfee, in the Laboratory's
Theoretical Studies Group, calculated the
reflectivity coefficient of the Moon.
Members of the Antenna and Mechanical Design,
Research Section, and other Laboratory groups.
Basic equipment selection criteria
No attempt was made to design major components specifically for the experiment. The selection of the receiver, transmitter, and antenna was made from equipment already on hand, including a special crystal-controlled receiver and transmitter designed for the Signal Corps by radio pioneer Edwin H. Armstrong.
Crystal control provided frequency stability, and the apparatus provided the power and bandwidth needed.
The relative velocities of the Earth and the Moon caused the return signal to differ from the transmitted signal by as much as 300 Hz, a phenomenon known as Doppler shift. The narrow-band receiver permitted tuning to the exact radio frequency of the returning echo.
Anticipating receiver design criteria
As DeWitt later recalled:
"We realized that the moon echoes would be very weak so we had to use a very narrow receiver bandwidth to reduce thermal noise to tolerable levels.
We had to tune the receiver each time for a slightly different frequency from that sent out because of the Doppler shift due to the earth's rotation and the radial velocity of the moon at the time."
Shortly after V-J Day, Lt. Col. DeWitt issued instructions to modify certain standard radar equipment for the moon investigation.
Changes to allow us to send out a long pulse. The transmitter was driven as hard as possible so we could get considerably more power from it, and an ordinary telegraph key was connected in the circuit to turn it on and off.
It was decided that a one-second pulse every four seconds would be satisfactory, so about ten minutes before moonrise I started to key the transmitter, for thirty minutes with no observable results.
After operating for about ten days, it became evident that the TR system was not working satisfactorily The TR tubes were not protecting the receiver from the strong transmitted pulse.
Engineers from the Antenna Design Section were called in.
J. Ruze, head of the section, and A. Kampinsky designed a system using quarter-wave step-up transformers on the 250-ohm line with open spark gaps on the ends of the quarter-wave TR and ATR.
But the gaps would not last because of the unusually bang pulses, although normally they work very well on conventional radar sets where the pulses are very short and the average power is low.
The next step was to design a mechanical TR system using an electro-mechanical keyer which bars on the transmission line, the keying being arranged that the shorting bars would have to be closed before the transmitter would go on.
But still we did not succeed in getting a response from the moon.
Part of the solution
The head of the Research section of the Laboratory, E. K. Stodola, W3IYF, Dr. Harold Webb and J. Mofensen, now part of the moon-radar group, decided that:
If two antennas could be mounted side by side on the same tower the additional 6 db. gain that, could be realized in the two-way system would be an advantage.
Engineers from the Mechanical Design Section were consulted. Under the able direction of J. Zorowritz this rather difficult feat was accomplished.
According to the reciprocity theorem, the transmitting and receiving patterns of an antenna are identical at a given wavelength
Now instead of 32 dipoles we had 64. The phasing of the dipoles was done by F. Haacke, P. Hartman and F. Elacker, ex. W2DMD.
During the time that the new antenna was being assembled and installed it was decided to utilize the narrowest band-pass possible in the receiver, to design an electronic keyer and sweep generator in order to operate a nine-inch cathode ray oscilloscope, and to measure the receiver sensitivity.
Test results found that 0.04 micro volts would equal the receiver noise, showing that the receiver was many times more sensitive than our previous ham receivers - although it should be noted that the band-width used (about 50 cycles) is much too narrow for voice communication (20 to 20,000 Hz)
At 2.7 m (111 Mhz) wavelength the antenna utilized ground reflection in order to increase the gain of the aerial beam, which was fixed at low elevation.
Tentative wiring configuration as per site description. Ing Luis A. Riesco NOTE: In 1971 the Army destroyed documentation and “Camp Evans history went up in smoke” InfoAge
Antenna Pattern and Considerations
The fundamental characteristics of an antenna are its Gain and the half power beamwidth (HPBW) angular separation between the half power points on the antenna radiation pattern, where the gain is one half the maximum value.
For this antenna the beam width of the array is approximately 15 deg at the half power point, with the first three lobes spaced approximately 3 deg in elevation.
9. “The SCR-270 in Japan” page 11 Fig 85, shows the “Expected vertical coverage diagram” For the 100 Kw Pk Pwr radar with a Westinghouse water cooled WL-530 tube. The antenna pattern for the “Final experimental version” was 500 KW Pk Pwr with two air cooled Triodes JAN6C21 using the same antenna the only difference is the distance in miles. It was concluded that:
Since the diameter of the moon subtends roughly one half degree of arc, most of the power transmitted does not illuminate the target, a serious waste of power. The transmitter was driven as hard as possible to get considerably more power from it, and reach the moon with the first lobe as instructed.
The rate of rise of the moon along its ecliptic is 1 degree of arc every 4 minutes, which allowed roughly 40 minutes of observation as the moon intercepted the first three lobes of the antenna.
Bending effects path through the ionosphere exist, but no precise measurement of this effect has yet been made.
How to reach the moon and detect a back signal Free space radar equation #1
On the same basis as Pt. The power gain due to ground reflections (not considered in the free space equation)increases the range of the system by a factor of 2.
This is equivalent to a power gain of 12 db. In the case of a target as large as the moon (2160 miles diameter), calculations showed that in order to receive an echo from the whole hemisphere of the moon at once, a pulse width greater than 0.02 seconds was required.
This set a lower limit on the transmitter pulse width which corresponds to an optimum bandwidth of 50 Hz for the receiver.
Propagation studies indicated that electromagnetic waves at a frequency of 110 Mz were capable of penetrating the ionosphere, and because of availability of equipment, a radar set operating at 111.5 Mz was chosen for the experiment.
Antenna effective gain
Efective area of the target #3 Summarizing
Maximum receiving range considerations
Summarizing all calculations
The "bedspring" mast antenna
Triode JAN6C21 Power Transmitter Stage
Year New Moon First Quarter Full Moon Last Quarter 1946 Jan 3 12:30 P Jan 10 20:27 Jan 17 14:46 Jan 25 05:00
The first echoes from the moon were received at moonrise on January 10, 1946
11:48 A.M. they aimed the antenna at the horizon and began transmitting. The first signals were detected at 11:58 A.M., and the experiment was concluded at 12:09 P.M., when the Moon moved out of the radar's range.
The modified radio receiver was an audible 180 cycle beat note occurring 2.5 seconds after transmission. Although numerous observations have been made, both at moonrise and moonset, echo returns do not occur after every transmission.
The radio waves had taken about 2.5 seconds to travel from Hearth to the Moon and back, a distance of over 800,000 km.
Camp Evans Audio, scroll down to “Project Diana - Radar Makes Round Trip to the Moon”
Sociology in Diana Experiment 2
Lt. Col. De Witt’s Experiment were of great influence on the later development of Earth Moon Earth (EME) communications
Mr. Trexler's idea for a communications relay capability using the moon
Project Pamor (Passive Moon Relay) was funded by the Naval Security Group.
With NAVSECGRU funding, Trexler's development teams built a 60-foot-diameter antenna (actually a reflector-shaped hole in the ground), at Stump Neck, Maryland, and with NRL in-house funding proceeded to experiment with T&R of signals off the moon.
1951- The feasibility study of using moon reflections communications was successful
1954- On July 25th, using a 100-watt 220-megahertz communications transmitter, NRL transmitted the first voice messages via the EME path.
1955- On November Transcontinental communications were demonstrated teletyping messages from Washington DC to San Diego; two months later NRL conducted transoceanic communications EME between Washington DC and Hawaii.
1956-The Chief of Naval Operations directed the establishment of the Communication Moon Relay (CMR) system for transmission of teletype and facsimile messages between Washington DC and Hawaii. Using 84-foot-diameter dish antennas-one for transmitting, the other for receiving.