AN ABSTRACT OF THE THESIS OF
BENJAMIN J BALLARD for the PROFESSIONAL in ENGINEERING (Name) (Degree) (Major)
Date thesis is presented June 1963
Title DESIGN, CONSTRUCTION AND OPERATION OF AN INTER-CITY
MICROWAVE NETWORK FOR^THE OREGON EDUCATIONAL TELEVISION SYSTEM Redacted for privacy Abstract approved* V (Major(Mail professor)
The fundamentals of microwave propagation are discussed relating to the conditions encountered in the operation of a microwave system in Western Oregon. A cost study is presented showing the price of purchasing and operating a microwave system as compared to leasing the service from a common carrier. The practical problems of installation and adjustment are pointed out along with the maintenance peculiar to the system. APPROVED: Redacted for privacy
Professor of Electrical Engineering Head of Department Electrical Engineering Redacted for privacy
Chairman of School Graduate Committee Redacted for privacy
Dean of Graduate School
Date thesis is presented June 1963
Typed by Marilyn K. Philo DESIGN, CONSTRUCTION AND OPERATION OF AN INTER-CITY MICROWAVE NETWORK FOR THE OREGON EDUCATIONAL TELEVISION SYSTEM
by
BENJAMIN J BALLARD
A THESIS
submitted to
OREGON STATE UNIVERSITY
in partial fulfillment of the requirements for the degree of
ELECTRICAL ENGINEER
June 1963 ACKNOWLEDGMENT
In the preparation of this paper the writer wishes to express
his thanks to Professor Louis N. Stone, Head of Electrical Engineering, for his suggestions and encouragement; to Professor Grant S. Feikert, Supervising Engineer, for the advice and help in compiling and editing
information contained herein; to Professor Samuel H. Bailey, Head of News Bureau, for his help and in making photographic equipment avail
able for use; and to Mrs. Marilyn Philo for her stenographic work in
editing and typing this paper. TABLE OF CONTENTS
Introduction 1
Basic Requirements ..... 1 Video Transmission By Lines 2 Video Transmission By Microwave 2
Engineering Design Considerations 4 Fundamentals of Microwave Propagation 4 Frequency Selection 7 Microwave Path Calculation 8 Path Attenuation 16 Equipment Requirements 13 Cost Analysis 23
Installation and Adjustment 25 Housing and Protection 25 Repeater Site . 33 Terminal Installation 34 Initial Equipment Adjustment 40
Operations 46 Capability of Network 46 Network Limitations and Reliability ...... 48 Operational Costs .... 50 Future Expansion 51
Bibliography 53
Appendix 54 Appendix I 55 Appendix II 58 Appendix III 59 Appendix IV 63 Appendix V 64 Appendix VI 65 ILLUSTRATIONS
Figure Number Title Page
1 Transmission Path Calculation 9
2 Vineyard Hill to Eugene Profile Chart .... 11
3 Vineyard Hill to Prospect Hill Profile Chart . . 12
4 Prospect Hill to Portland Profile Chart .... 13
5 Fresnel Zone Clearance Chart 15
6 Free Space Attenuation Graph 17
7 Map of Inter-City Microwave System ..... 26
8 Villard Hall, University of Oregon 27
9 Microwave Transmitter and Antenna at Villard Hall. 28
10 Microwave Transmitter and Antenna at the Coliseum. 29
11 The Coliseum, Oregon State University .... 30
12 Channel 7 Transmitter Building at Vineyard Hill . 31
13 Microwave Receiver and Antenna 32
14 Parabolic Antennas at Vineyard Hill ..... 35
15 Channel 7 Transmitter Console 36
16 Motorola MV-30 Microwave Equipment at Vineyard Hill 37
17 Microwave Repeater Equipment at Prospect Hill . . 38
18 Microwave Repeater Site at Prospect Hill ... 39
19 Parabolic Antenna with Radome Cover 41
20 Microwave Antenna System at Portland 42 DESIGN, CONSTRUCTION AND OPERATION OF AN INTER-CITY MICROWAVE NETWORK FOR
THE OREGON EDUCATIONAL TELEVISION SYSTEM
INTRODUCTION
When it became evident that the Federal Communications Commission had reserved television channels for educational use, the State System of Higher Education began studies to employ television in the educa tional program of Oregon. An inter-institutional committee, composed of James M. Morris, General Extension Division; D. Glenn Starlin,
University of Oregon; and Grant S. Feikert, Oregon State College, was appointed by Chancellor Charles D. Byrne for this study. This commit tee submitted its report to Chancellor Byrne on July 1, 1952. The report was accepted by the State Board of Higher Education in August of 1952.
Not until several years later, when funds from grants and legis lative appropriation were made available, did educational television become available in Oregon. From the onset planning had been on the basis of inter-institutional participation.
BASIC REQUIREMENTS
In order to develop this concept of inter-institutional partici pation, it would be necessary to connect or tie the schools together into a "network" for the common use of courses to be telecast. The requirements for transmission of video signals are quite different from methods used for audio signals. Radio has been used for a number 2 of years as a means of making available to the public as well as for in-school listening, information originating from various places throughout the state or nation. All information necessary for a standard radio broadcast is contained in the relatively narrow band of audio frequencies (30 to 7500 cycles per second). These audio signals are readily fed from one place to another over a metalic pair of wires, normally thought of as telephone lines.
Video Transmission By Lines
The video signal, which is standard in the industry today, occupies a band of frequencies from zero to four and one-half mega cycles per second (0 - 4.5 mc). This wide band of frequencies can not be transmitted over "regular telephone" wires without suffering serious losses. Coaxial cables, which are of special construction, are used for transmission of video signals as well as other types of high frequency signals. These coaxial cables do have some disadvantages or limitations, chief of which is the cost factor.
Another limitation is the relatively high loss of signal in the line, which necessitates the frequent use of repeating amplifiers to restore signal level in long transmission lines.
Video Transmission By Microwave
A third method of signal transmission which has developed rapidly over the past few years is the use of the microwave band of frequencies. As the name implies, these frequencies are of very short wave length, or as is classified in the frequency spectrum 3
"super high frequency," being from 3,000 to 30,000 megacycles per second. With the development of equipment for generating and utilizing these microwave frequencies, great advancements have been made in the communications field. High on the list of uses for microwave equipment is the simultaneous transmission of video and
audio signals as employed in television broadcasting. Television
studios no longer need be adjacent to the television transmitter
but may be located at a more convenient place. A studio-to-trans
mitter microwave link can then be used for transmission of both
video and audio signals from the production studio to the main
television transmitter.
Educational television in Oregon became a reality in the fall
of 1957. At that time production studios located in the Coliseum
at Oregon State University in Corvallis and in Villard Hall at
University of Oregon in Eugene supplied program information to the
Channel 7 transmitter located at Vineyard Hill five miles north of
Corvallis. These studios were linked to the transmitter by micro
wave equipment operating in the 7,000 megacycle band of frequencies.
Further expansion of educational television in Oregon was
realized on February 6, 1961, when KOAP-TV in Portland joined KOAC-TV
in Corvallis to form the Oregon Educational Television Network. The
studio and transmitter of KOAP-TV are linked with the KOAC-TV trans
mitter and studio by a two-way microwave network.
With the present microwave system it is possible to transmit in
both directions simultaneously, with one video and two audio channels, 4
between the Corvallis and Portland studios. In addition, one video and one audio channel are transmitted from the Eugene studio to the
KOAC-TV transmitter. This makes it possible for a program origi nating in any one of the three "live" studios to be broadcast on either or both Channel 7 or Channel 10 transmitters, or to be video tape recorded at either the Corvallis or the Portland studios.
ENGINEERING DESIGN CONSIDERATIONS
Microwave relay systems utilize a transmission path which is only partially controllable by the user or installer of the equipment.
Thus the performance and the reliability of the system will depend not only upon the equipment, but upon the quality of the path over which it must operate. It is necessary therefore, for careful planning to be given to the microwave system prior to installation. It is in this planning that the engineer assumes the major role in determining requirements based upon terrain conditions, meteorological effects, and the microwave principles.
Fundamentals of Microwave Propagation
It is popularly assumed that the microwave energy travels in a
"beam" from the transmitter antenna to the receiver antenna, similar to a beam of light produced by a searchlight. Since both light waves and microwaves are forms of electromagnetic radiant energy, it follows 5 they both are subject to the same laws and display similar character istics. The analogous properties includes
a. Obstruction or attenuation of the energy by solid
objects such as hills, buildings, trees, etc.
b. Reflections from flat surfaces such as sides of
buildings, smooth terrain, water, and layers of
still air.
c. Diffraction around edges of solid objects.
d. Refraction, or bending by the atmosphere.
Line of Sight. In order to assure reliable operation of a micro wave system, special considerations must be given to path selection with regard to the forementioned properties. "Line of sight" or optical clearance over a microwave path is not satisfactory. It is necessary to have what is called Fresnel Zone clearance. If antennas are properly aligned, the region in which the useful radiated energy is concentrated, is in the center of the beam radiated by the trans mitting antenna. Within this beam is a region called the first
Fresnel Zone. This Fresnel Zone is contained within a ficticious curved boundary from which any reflected signal would travel an additional one-half wave length in going from transmitter to receiver.
Any reflection from a surface within this Fresnel Zone boundary will not have the full added half-wave length of travel and thus will arrive at the receiver as a partially or totally cancelling signal.
For this reason this zone must be kept free from all obstructions or potentially reflecting surfaces. Similarly there is a second 6
Fresnel Zone boundary via which the added path travel is one wave length; a third zone with added travel of one and one-half wave length; etc. Reflections from these boundaries are alternately aiding and cancelling.
Reflections. The reflection characteristics of microwaves can be either an asset or a liability. Passive reflectors, which are large pieces of flat metal, are often used to reflect and redirect the microwave beam. However, reflections which occur from uncontrol lable atmospheric conditions or from flat earth or water surface can be detrimental to the operation of a system. Atmospheric conditions can produce an abrupt difference in dielectric constant at a point within a Fresnel Zone which provides a good reflecting surface momentarily. This can result in a cancelling signal arriving at the receiver and cause a drop out of the total received signal strength. This condition is one cause of a fade and is normally of very short duration, but may be rapidly repetitious.
Refraction. If the atmosphere were perfectly homogeneous, the transmitted energy would travel in a straight line to the receiver.
In the lower atmosphere both temperature and water vapor pressure normally decrease with increase in altitude, causing a corresponding change in the index of refraction. This decreasing index of refraction causes the microwave beam to travel at slightly greater velocity at higher altitudes. The net effect is that the beam is bent downward. This effectively increases the horizon much the same as reducing the curvature of the earth. This effective reduction in 7
earth curvature, or effective increase in earth radius, is expressed
by the equivalent earth radius factor K:
Where K = 1.33 x true earth's radius.
A homogeneous atmosphere is the most common condition found.
However, weather changes will produce variations in the refractive
index of the atmosphere. A decrease in temperature at high eleva
tions (or the presence of water vapor) will tend to bend the micro
wave beam upward, away from the earth. This is referred to as
inverse beam bending. A rise in temperature with elevation will
produce the opposite effect, bending the beam downward toward the
earth.
Multi-path fading can result when part of the microwave beam
is refracted toward the earth and then reflected from the surface,
where it arrives at the receiving antenna out of phase which results
in fading.
The planning of a microwave system requires that consideration be given to all of the propogation characteristics in order to achieve reliable operation.
Frequency Selection
The Federal Communications Commission has set aside two bands of frequencies (1,990-2,110 mc/s; 6,875-7,125 mc/s) to be licensed for television remote pickup and STL (studio, transmitter links). The design of a microwave system path is dependent upon the frequency used. A transmission path designed for one frequency band may, (but 8 chances are great that it may not) give satisfactory operation at the other band of frequencies.
There are a number of factors in the design of a microwave system which will be the same regardless of which frequency band is used. However, many considerations are dependent upon frequency such as free space attenuation, transmission line and antenna efficiency, necessary transmitter power output, and receiver design.
A comparison of performance is shown in Figure 1, of the two frequency bands (7,000 mc and 2,000 mc). The relative power level is expressed in db at each side of the chart. In this particular path a 10 db advantage has been shown in favor of the 7,000 megacycle equipment. In other paths this advantage may turn to a disadvantage depending upon:
a. Antenna and reflector size and spacing.
b. Receiver noise figures, etc.
c. Length of transmission line.
d. Length of microwave path and free space attenuation.
e. Transmitter power output.
Microwave Path Calculation
There are no clear-cut lines of demarcation to show one frequency better suited for use than another. After considering many factors, it was decided to use the higher or 7,000 megacycle band for the micro wave network. Next came the selection of a transmission path over which to operate the system. POWER LEVEL (dbw)
1. Transmitter Output 2. Transmission Line Loss X 3. Antenna System Gain
2 I
> 4. Free Space Loss * i i 5. Antenna System Gain
6. Transmission Line
7. Recv. Noise Figure 8. Net Advantage Y
POWER LEVEL (dbw) 10 A preliminary paper survey was made to determine or provide
information on:
a. Preliminary cost estimates of the system.
b. Provide information for the FCC.
c. Determine tower heights for proper Fresnel
Zone clearance,
d. Determine number of repeater stations (if
any) needed.
Topographic maps of the area contain a wealth of information and are used to lay out several alternate paths. Factors to consider on sight selection of a terminal station or repeater station are?
a. Accessibility by all-weather roads.
b. Elevation.
c. Availability of power.
d. Soil condition.
o. Length of transmission path.
f. Type of intervening terrain.
g. Availability and cost of land,
h. Zoning regulations.
After fixed sites are determined their locations are plotted on a topographical map and a straight line is drawn between locations.
A profile chart can then be plotted on special **/3 earth's-radius graph paper, as is shown in Figures 2, 3 and 4. This is done by taking the elevation of intervening points from the map and plotting elevation vs. distance on the special profile graph paper. 11 12
14
Information contained in the profile charts along with the use
of the chart in Figure 5 can be used to determine the necessary
tower heights for proper Fresnel Zone clearance.
The use of maps cannot be completely relied upon in microwave
path selection. The best of maps might be inaccurate in some detail.
An on-the-spot survey is essential before the final selection is made.
Man-made obsticals to the line of sight may exist which would not be
shown on the map. Trees could completely block the path, and this
factor would not be shown on the map.
One of the most practical methods of checking a path for line
of sight clearance is the use of a beam of light during the hours of
darkness. A flashing light, coded in a recognizable manner, is placed
at one end of the path and if it can be observed from the other end
of the transmission path, the line of sight clearance is assured.
In Western Oregon however, weather conditions make it difficult
if not impossible to see over the total path length. Also the use of
lights become difficult where many other flashing lights exist such as in the proximity of a city.
Another method used to check the terrain of a proposed micro
wave path is to fly over it in an airplane. The elevation of the intervening terrain can be double checked by flying along all or portions of the path. The plane is flown at the calculated or plotted elevation at which the microwave beam would be. The visual clear ance along the path can be checked by both pilot and observer, looking simultaneously in both directions along the proposed path. 1/2 FIRST FRESNEL ZONE CLEARANCE IN FEET-(S/2)
ro <>J * *> Cn (Jl Ol Ol ->i CJi O w o en O en O CD O Ul o en o 1— \ \ \ \ \ \ k> \ 2 : ho ^^^
m r \ 1 I •noio o ( 1-s *" \\ *> £ X ™ <> & t 5 Ol 3, _, V^^ \ ± 1 . » 1 \ »: " pi > \o» fl "0" *» m to 7^
i O T 5TO84 r 3 APPLIC/ i \ ± k LCULATf ;_ 2 CDO HO 5 r »r-n mOS \\ R/ H g \v en H > vn Z o m Ii
m "> rv> -1 ° o ^ o 1 o 1 k V (Jl Uk o V ^ \ (J) -+H1 1 1 \ ^i \ o -roc-* uio^ioxOq - 5 g c-
DISTANCE TO OBSTACLE IN MILES-(A) (A) IS LESS THAN OR EQUAL TO (D/2)
£l 16
Path Attenuation
When the transmission path is covered in one hop, the length is fixed by the location of the terminal sites. Where one or more repeater stations are required, the length will be divided into various lengths. The attenuation of each path can be determined by the use of the chart of Figure 6. The free space attenuation in db between isotropic antennas is given by the formula:
A« 36.6 + 20 log F t 20 log D
Where: A» free space attenuation, in db
F• frequency, in megacycles per second
0 * distance, in miles
Under free space conditions, the radio energy spreads out according to the inverse square of the distance, as in optics. An isotropic antenna is, by definition, one which radiates or receives energy equally well in all directions. Though not physically realizable, the isotropic antenna serves as a convenient reference.
If there were no terrain or atmospheric effects, the problem of determining suitable antenna heights and sizes would be a simple one.
Unfortunately, all microwave sites are not on mountain tops and the index of the refraction of the atmosphere is neither linear nor is it stable for a long period of time. The best one can hope for in dependable operation of a microwave system is to consider all of the known factors affecting transmission and to select equipment (within practical reason) which will give the necessary performance. DIAMETER IN FEET m • >j a o o
100 PATH LENGTH IN MILES
FIGURE 6 18
Equipment Requirements
After calculations have been made as to free space attenuation, and antenna heights for a given path, the selection of equipment is the next step. One of the major criteria used in the selection of equipment is the purpose for which it is to be used.
There are many uses of microwave with as many different equip ment designs. There are microwave systems designed for message circuit transmission capable of handling in excess of 600 telephone circuits simultaneously. Other systems are designed for relaying information for high speed data processing computors. This study, however, is concerned with equipment designed for the purpose of relaying television signals both visual and aural, and the effec tiveness with which the job is done.
In the United States the broadcast industry is regulated by the Federal Communications Commission. This Commission establishes standards to which the individual broadcasters must comply if they are to retain their station licenses. These standards are then reflected in the operating performance of the equipment. The ability of equipment to meet FCC requirements is considered in selection of equipment, along with other requirements for the individual installation.
In Appendix I specifications are listed for equipment perform ance expected for the Oregon Educational Television Microwave Network. 19
In addition to those specifications it wa3 also necessary for the equipment to meet these requirements:
a. Be of a type approved by FCC for use in television
STL and inter-city relay service.
b. Be capable of simultaneous two-way transmission
of one video channel (0 - 4.5 megacycles), and
two audio channels (30 - 15,000 cycles) each.
c. System signal to noise ratio shall be:
Video signal (peak-to-peak) to RMS noise 55 db
Audio signal RMS to RMS noise 57 db
d. Predicted reliability of the system greater than
99.85%.
Simultaneous Two-Way Transmission. The ability of a system to operate in this manner is dependent upon isolation and rejection circuits built into the equipment.
Basically, this means the microwave transmitter output and the microwave receiver input, share the same antenna and wave guide. The transmitter can be transmitting one program on a given frequency and a different program can be coming to the receiver through the same antenna system on a different frequency, without any interference or reaction between the two.
To accomplish this, the receiver "RF plumbing" contains compo nents which (1) accept the incoming microwave signal from the antenna system and (2) reject adjacent channel and image frequencies which are produced by the transmitter sharing the same antenna system. The rejection of these unwanted frequencies is obtained by means of a 20 five-cavity maximally flat filter, which is factory tuned to the assigned received signal.
A ferrite isolator is also placed between the transmitter and the wave guide antenna system. This is a unilateral wave guide transmission device which isolates the transmitter klystron from the antenna system, thus preventing distortion of the modulation characteristics of the klystron due to reflected or incoming energy from the microwave system. It allows the transmitted energy to pass with less than 1 db of attenuation, but attenuates energy in the reverse direction by more than 40 db. These isolators can be seen in
Figure 17.
Ferrites are ceramic members of the ferromagnetic class of materials. Being ceramics, ferrites possess high resistivities (from 102 to 107 ohmmeters), which tend to reduce eddy currents.
They are useful at microwave frequencies because the absence of eddy currents reduce the losses in ferrites and allows the micro wave energy to enter the ferrite material and interact with the electron spins.
Antenna Gain. An example is shown in Appendix II how one manufacturer of equipment set about to determine the type and size of antennas required and the lengths and losses of wave guides, in order for his equipment to meet the system specifications. A computation like this is necessary for each transmission path of the system. The finally installed antennas for this particular path were not as stated in this calculation. This example is used 21 to show tabulating method of arriving at a signal to noise ratio of a given path. It also points out that there are more than one given
combination of antennas for achieving the same end results.
A graph used for determining the gain for different sizes of parabolic antennas is shown in the upper left-hand corner of Figure 6. The gain of an antenna is expressed in db relative to an isotropic radiator which is a theoretical antenna that radiates equally well in all directions and has a gain of unity. The parabolic antennas increase the effective radiated power by focusing the energy into a
narrow beam that can be directed to the receiving antenna.
Transmitter Power. The "super high frequency" of the microwave signal in any large amounts of power is rather difficult and expen sive to obtain. It has been a relatively short period of time since equipment has been developed so that the microwave frequencies can be utilized. In general practice today, the equipment for television STL use is rated at transmitter power output of one watt or one-tenth of a watt. This amount of power, though it seems small, when focused into a beam by the parabolic antenna is sufficient for this type of service.
In the design and specifications of this microwave network, all transmitters were to have output power ratings of one watt. Two of the transmission paths in the system are such that one-tenth watt transmitters would have been sufficient power. For sake of uniformity of equipment and stocking of spare parts, plus the added margin of 22
safety, it was felt economically wise to have all transmitters capable of the same power output.
Stability. The reflex klystron is the type of oscillator used in the transmitter for producing the output power. The stability of oscillation is maintained by one of two methods, (1) the klystron itself is housed in a temperature controlled compartment where the temperature is held constant and (2) an Automatic Frequency Control
Circuit (AFC) is employed which applies a corrective voltage to the repeller electrode to compensate for a change in frequency.
Multiplexing. In order for the equipment to transmit and receive more than one band of frequencies without inter-action between them, a process called multiplexing is used. Consider first the video signal. It is composed of frequencies from zero up to 4.5 megacycles. If no multiplexing is used, only the video signal is used to frequency modulate the klystron oscillator.
Specifications call for audio channels to be transmitted in addi tion to the video information. This is done by frequency modu lating a subcarrier frequency (6.5 megacycles) with the audio frequencies, then adding this modulated subcarrier to the video signal. The combined signals then modulate the klystron oscillator. If more than one subcarrier is used, another subcarrier frequency (say 5.9 or 7.1 megacycles) is modulated by a second audio signal and added to the video signal which in turn modulates the klystron oscillator. 23
At the receiving end of the system the FM modulated carrier is
demodulated and amplified. FM receivers tuned to the subcarrier
frequencies then pick off the 6.5 rac and/or the 5.9 mc frequencies.
These subcarrier frequencies when demodulated deliver the original audio signal. The video signal is then fed through a "low pass"
filter which has a cut off frequency of 4.5 megacycles. This
permits only the video signal to pass and all higher frequencies
are attenuated.
Band Pass Characteristics. When multiplexing audio channels along with the video channel, the equipment must have the ability to
transmit and receive this wide band of frequencies. In the example
just mentioned, it must have a band pass capability of 7.1 mega
cycles without excessive losses at the higher frequencies. The spec ification of equipment as given in Appendix I states the frequency response must be flat within £ 0.5 db from zero up to a frequency of
7 megacycles. This is another way of specifying band pass capabil
ities up to a 7 megacycle frequency.
Cost Analysis
Sooner or later the question will inevitably arise; how much will
it cost?
After all engineering factors have been considered, the trans mission paths have been determined, and the type of equipment speci fied, it is time to examine the cost factor. Will it be more economical to buy, install, and operate the system; or will it be 24
better to buy the service on a monthly basis from a company or
organization licensed as a "common carrier" that can furnish this
service?
The Oregon Educational Television Microwave Network was
installed in two different segments. The initial installation of
equipment, which was for the Eugene-to-transmitter and the
Corvallis-to-transmitter link was type TVM-1A microwave equipment
supplied by RCA. The cost of this equipment was included in the total "package deal" price for supplying the studio and transmitting television equipment. The cost of microwave equipment has been singled out and estimated to have been about $18,000, The instal lation cost has been estimated as amounting to about 5% of the equipment cost.
The three and one-half years of operating the RCA microwave equipment gave a good indication of the yearly operating expense.
When the next and larger segment of the microwave system, which connects the Portland studio and transmitter with Corvallis and
Eugene, was to be installed a good knowledge of installation and operational cost had been acquired.
The table shown in Appendix IV shows a comparison of the total cost of purchasing, installing, and operating the present microwave network with what it would cost to lease this service from a "common carrier." 25
INSTALLATION AND ADJUSTMENTS
The final transmission path selection for the microwave network is shown by Figure 7. This map of the system is shown superimposed
upon a topographic map of the lower Willamette Valley area. The
topographic features of a map of this size are of necessity limited
to a small scale. Nevertheless, it is possible to see that the
microwave paths traverse the relatively flat and level valley areas in order to obtain the long path lengths. The terminal and relay
sites are located on convenient and accessible higher points of
elevation.
Housing and Protection
The particular equipment and its design dictate to a large extent
the type of housing necessary. The TVM-1A RCA equipment is designed
so that it could be portable. The transmitter and antenna are built
as an integral unit. The receiver unit has the same construction,
with the local klystron oscillator and IF pre-araplifier mounted as one
unit with the antenna and wave guide feed. Since these units must be mounted high at the antenna placement site, they are connected with
their control units by coaxial cables. Installations of these units
are shown in Figures 9, 10 and 13. The windows used to protect units from weather are of corrugated fiberglass construction. These windows as seen in Figure 12 were built square so they could be oriented to determine which way the least attenuation was offered to microwave signal passing through them. It will be noticed that corrugations are FIGURE 7 27 *y
FIGURE 8 - Villard Hall on the University of Oregon campus. The Eugene microwave transmitter is enclosed in the housing atop the parapet at the left. 28
FIGURE 9 - The RCA TVT-1A transmitter and 6 foot parabolic antenna mounted behind corrugated fiber glass window atop Villard Hall. 29
FIGURE 10 - RCA TVT-1A transmitter and 4 foot parabolic antenna atop the Coliseum building in Corvallis. Microwave transmitter enclosure
Receiving antenna
FIGURE 11 - View of the north side of the Coliseum showing location of the transmitter and the 4 foot receiving antenna. o 31
«^*'Mr>, -w FIGURE 12 - View of the south side of Channel 7 transmitter building on Vineyard Hill. Note the polarization of the fiber glass windows, behind which are mounted microwave antennas. 32
FIGURE 13 - RCA TVR-1A receiver with a 4 foot parabolic antenna. Vertical polarization is obtained by the 90° twist in the waveguide feed. 33
horizontal on one window and vertical on the other two. This is
because the polarization of the wave guide feed is different on the different links. The corrugations of the fiberglass lend a polarizing
effect to the window, hence the orientation for least attenuation.
The attenuation between horizontally and vertically polarized antennas will range between 20 and 30 db. This is an added method of isolating
adjacent channels to prevent possible interference.
The Motorola MV-30 microwave equipment is rack mounted inside the building and connected with antennas by runs of wave guide. It has previously been pointed out in the calculation of system losses,
the necessity for short wave guide runs. These losses amount to about 2.0 db per hundred feet of wave guide. This equipment, there fore, is installed as near as possible to the tower or supporting antenna structure in order to reduce wave guide loss.
Repeater Site
At the time the survey was made for this microwave system, many other systems for other types of service had been installed.
As a result, the favorable repeater sites were already occupied. The law of supply and demand quickly takes over making these locations quite expensive to acquire.
Easements. The State of Oregon was fortunate in this case, in as much as a successful contract was negotiated with the
Bonneville Power Administration for the sharing of their location atop Prospect Hill approximately 8 miles south of Salem. Space was made available for construction of a 10' x 12' metal building to 34
house equipment, and permission granted for the mounting of parabolic
antennas at the 40' elevation on the already existing tower. This
repeater site showing location of buildings, tower, and placement
of antennas is seen in Figure 18.
There were a number of stipulations in the contract particularly
regarding interference with already operating equipment and systems
at the site. These conditions were readily complied with and amiable
relations have been maintained by this joint occupancy.
Antenna Mounts. In order to mount the antenna "dishes" and wave
guide runs on this tower, it was necessary to add several cross
members to the tower. Specifications were that any steel mounted
on the tower must be galvanized to prevent rusting. The mounting
brackets with necessary mounting hardware were designed and built
in shops at Corvallis. They were then taken to Portland as a complete unit to be galvanized before they were installed on the tower.
Terminal Installation
The Vineyard-to-Portland terminal sites of the microwave link are at the television transmitter locations. The television antenna towers in both cases are used for mounting the microwave antennas also. The antenna at Vineyard Hill .looking toward Prospect Hill is mounted 140 feet up on the tower. This height above the terrain was necessary in order to clear the tall fir trees adjacent to the tower.
The antenna system at the Portland site consists of a two-foot parabolic reflector, mounted atop the small microwave house, looking vertically to a passive reflector mounted 70 feet up to the tower. FIGURE 14 - Parabolic antennas at Vineyard Hill. The transmitting antenna on the left is fed by a flexible waveguide. Receiving unit on the right has the klystron oscillator and IF pre amplifiers mounted as an integral \ it with the antenna. FIGURE 15 - Racks of equipment and control console at Channel 7 transmitter. Equipment in third rack from left is RCA microwave receiving units associated with antennas in the loft above. FIGURE 16 - Motorola transmitters (two racks on left) and Motorola receiver (third from left) at Vineyard Hill. Sharing of a common waveguide is seen at the top of transmitter and receiver racks. FIGURE 17 - Motorola receiver and transmitter units at Prospect Hill microwave repeater. Notice the ferrite isolators in waveguides at the output of the transmitters. FIGURE 18 - Microwave repeater site at Prospect Hill showing the antennas mounted on the Bonneville Power Administration's tower. Small building at the right houses microwave equipment as shown in Figure 17. 40
A view of the parabolic antenna with a radome cover is shown in Figure 19, The radorae is constructed of a special low loss material, which prevents the dish from becoming filled with snow, ice, leaves,
etc. The "S" shaped connection under the antenna is a length of
flexible wave guide coming from the top of the equipment racks within
the microwave building. Figure 20 shows the mounting of the passive
reflector on the tower with respect to the antenna below it.
The transmitter and antenna installation at the Eugene terminal is in Villard Hall on the University of Oregon Campus. The TV studio
and control room are located on the third floor of the building. A
small sheet metal structure with fiberglass window was constructed
atop a parapet on the northeast corner of the building as seen in
Figure 8, for transmitter housing.
The Corvallis TV studio and control room is located on the balcony level in the northeast corner of the Coliseum on Oregon
State University campus. The transmitter is housed in a small
plywood shelter with fiberglass window and located on top of the
Coliseum building as seen in Figures 10 and 11. A four-foot antenna
(receiving from Vineyard Hill) is mounted on the north side of the
Coliseum near the top. The location of this antenna is seen in
Figure 11.
Initial Equipment Adjustment
After the installation of the equipment was made and the source of power connected, the first adjustment of consequence was to tune FIGURE 19 - Parabolic antenna at Portland with a radome cover. It is connected by flexible waveguide to the transmitting and receiving equipment in the building directly beneath. 42
Passive Reflector
FIGURE 20 - Antenna system at Portland microwave terminal showing the position of the passive reflector on the tower to the antenna mounted directly beneath. 43 up the klystron oscillator and get it operating on the proper frequency with rated power output.
Klystron Adjustment. The klystron is so mounted that it becomes a part of the RF "plumbing" section of the transmitter.
The term "plumbing" is applied because of the physical appearance of this unit. The circuits consist almost completely of wave guide sections, which are adjusted by plungers or slugs to change the physical as well as electrical lengths of the circuits.
The reflex klystron tuning is a dual function process. The output frequency is controlled by a combination of mechanical adjustment of the cavity and variation of the d-c voltage applied to the klystron repeller electrode. The RCA type TVT-1A trans mitter is designed to operate over a relatively wide band of frequencies. Using an associated wavemeter, this unit can be tuned up in the field to operate over the frequency range from
5,925 to 7,125 megacycles. On the other hand, the Motorola type
MV-30 transmitter is pretuned at the factory for operation on a single specified frequency. In either case, the klystron tuning is the same, its operating conditions must be adjusted to the wave guide cavity into which it works.
Virtually the same adjustments are made in tuning the klystron local oscillator in the microwave receivers. However, they are tuned to a frequency of 75 megacycles below the incoming signal.
This difference in frequency establishes the IF frequency of 75 mc for the receiver amplifiers. 44
Antenna Alignment. The microwave beam has previously been compared to a beam of light. If the system is to be adjusted for optimum performance, the antennas must be aligned so that they are
"looking" directly at each other. The alignment can be accomplished after the transmitters and antennas are radiating a signal.
Initially the antennas are oriented (looking toward the antenna at the other end of the microwave path) by eye, or by use of a compass or transit. When the alignment becomes sufficiently close that a signal can be received, the strength of the received signal can be observed as the limiter current on the microwave receiver. The parabolic antenna is then swung through a horizontal arc to a point where received signal is maximum. When the horizontal plane has been established and secured, the "dish" is then swung through a vertical arc for maximum received signal. When the antenna on one end of the microwave link has been adjusted for optimum performance, the same procedure is performed with the antenna at the opposite end of the link. These fine adjustments of the antennas are alternately made several times or until no further increase in signal is obtained.
The mounting clamps are then tightened so that the antennas cannot be knocked out of alignment by gusts of wind, ice loading, or any other external force.
The alignment can be greatly accelerated if two-way radio communication is available. Communication in some form is needed so that the adjusting operations can be coordinated. 45
Fine Adjustments. Now that the RF signal is being transmitted over the microwave system, the fine adjustments can be made on the equipment. Automatic Frequency Control Circuits (AFC) are incorporated in the receiver units so that if a difference in frequency other than
75 mc occurs, between the incoming signal and the receiver klystron, a corrective voltage is applied to the klystron repeller electrode.
Thus a constant tuning is maintained on the incoming signal.
The adjustment of signal levels throughout the system is the next important step. The standard video signal is composed of frequencies (0 to 4.5 mc) which mu3t be transmitted so that the received signal is the same in all respects to the signal fed into the system.
Special test equipment which produce a "multiburst signal" is useful in adjusting microwave systems as well as other video equipment. The "multiburst signal" contains the horizontal sync pulse plus seven bands of frequencies. Frequencies of d-c, 0.5,
1.5, 2.0, 3,2, 3.6, and 4.2 megacycles are produced in bursts which can be observed on an oscilloscope. If a "multiburst signal" with all frequencies of equal magnitude is fed into the system and then measured with the oscilloscope at the system output, the frequency response can be observed and adjusted.
The microwave equipment circuits contain low frequency, mid frequency, and high frequency compensating networks. By proper adjustment of these networks the frequency response of the system can be adjusted to be flat over the useful range. 46
The system levels were set up using an oscilloscope to measure
peak-to-peak voltage. The gain of the equipment was then adjusted
so that when a video signal of 1 volt (p-p) was fed into the system
1 volt (p-p) was delivered at the receiver output.
Audio level adjustments were necessary to prevent cross talk
between the two audio subcarrier channels, also to keep sound bars
out of the video signal. The input and output impedance of the audio
equipment is 600 ohms, and in keeping with industry standards audio
levels of 0 db were set up for system operation.
OPERATIONS
Capability of Network
After almost six years of operating the first segment and
slightly over two years the second segment, an appraisal can be
made of the microwave network. The original network and switching system, which were designed for the utmost in flexibility, have
proven satisfactory in all combinations of switching operations.
For a period of time after the Vinayard-to-Portland link was installed, trouble was experienced in its operation. The system was operative but the signal quality was not entirely satisfactory. The video signal contained a 60-cycle component, also at times the sync components of the signal would be stretched to an excessive value.
These troubles were easily cleared up once the equipment and its operations became more familiar. One particular tube in the video modulator was subjected to overloading by improper circuit design. 47
This unit was eventually replaced with a newly designed modulator which solved that particular problem. At the time the modulators were replaced, it was necessary to reset signal levels throughout the system. This adjustment improved the quality of the signal very much.
The second subcarrier audio channel did not give satisfactory performance until November of 1962, when the manufacturer's field engineer made a diagnosis and concluded that the frequency of its operation was improperly selected. The frequency of 7.1 megacycles was out on the extreme edge of the systems band pass ability. This was indicated when the overall frequency response of the system was taken. As shown in Appendix V at the frequency of 7.1 mc the system response was down by 9.25 db. The subcarrier transmitters and receivers were then sent to the factory and retuned to a frequency of
5.9 megacycles at which frequency they give satisfactory performance.
The microwave network is capable of and has been in operation under a complicated transmission and switching arrangement. There have been times when programing schedules call for programs originating in Corvallis studio to be aired on Channel 10 transmitter in Portland, while the program produced in the Portland studio is being transmitted on Channel 7 transmitter at Corvallis. Simultaneous with these programs being transmitted, a third program originating in the Eugene studio is microwaved to the Corvallis studio via Vineyard Hill for video tape recording. All of these simultaneous microwave trans missions were accomplished without interference or interaction. 48
Network Limitations and Reliability
It is a recognized fact that there are limiting factors which apply to equipment, to systems and also to human factors. As soon as the network was in operation, some demands were made which could not be met. After the limitations were recognized, it has been much easier to maintain normal operation of the system.
Equipment. The limitation of the equipment was generally understood before the installation, however, certain factors arise which are unpredictable. There are seven transmitters in the system of which only two have given concern about their operation.
One transmitter has a tendency to drift in frequency. The drift is slight but is within the limits of its assigned frequency. However, any noticable drift is of concern. Any frequency change is compensated for by the AFC Circuit in the associated receiver, which keeps the receiver tuned to the transmitter frequency through out this slow drift. Another transmitter, located at Prospect repeater, operates normally in all respects that can be determined, except the life of the klystron oscillator has been much shorter than it should be. The two transmitters sitting side by side, as seen in Figure 17 have been tested and checked in comparing their operations. In one transmitter the original klystron oscillator is still in use after about 27 months of operation, whereas the klystron oscillator in the other transmitter has been replaced three times in that length of time. This condition could be the fault of the individual klystron oscillator tubes and not the transmitter, a factor which additional time will prove or disprove. 49
The performance of individual components or smaller pieces of equipment can be anticipated and predicted quite accurately. However, when a complex network is composed of many individual components the results are not always fully predictable. One particular link in the microwave network will at times display some radio frequency (RF) interference. This condition is of a transient nature and is not always present. Many theories of its cause have been proposed but to date no solution has been found for this problem. The presence of this interference shows up as a very faint "herring bone" pattern on the picture tube of the monitor or TV set.
The reliability of the equipment is now largely dependent upon its maintenance. A schedule of preventive maintenance has held the loss of "on-the-air time" due to equipment failure to a very small factor.
Weather. The effect of atmospheric conditions upon the operation of the system has been very slight. However, this factor does have an effect and is one time when the human element can do nothing but stand by and observe.
The months of December and early January, when the valleys are filled with fog, are the time when fading of signal is most noted.
Under these conditions the fog blanket may be only a few hundred feet thick, while one end of the microwave path is above in bright sunlight.
The lack of air turbulence allows conditions to build up which are conducive to inverse bending and multipath effects. The most severe conditions experienced have caused rapid fades lasting only 5 to 10 50 seconds and at frequency intervals of every 1 or 2 minutes. Condi tions of this nature have lasted for only about 1/2 hour duration, usually when operations first begin in the morning about 8:30 a.m. to 9:30 a.m. or again late in the evening after 6:30 p.m.
The propagational reliability of the microwave system here in the Willamette Valley of Oregon has been proven to be very good.
A definite record has not been kept of the loss of time due to fades, but an estimate shows the Percentage of Reliability to be 99.99%.
Operational Costs
Some of these operating costs are fixed or can be computed with a fair degree of accuracy while others must be estimated. Part of the microwave system has been in operation almost six years, while the remainder has been operating for about 27 months. Over this period of time estimates of the yearly operating costs can be computed.
The unexpected can always happen; such as storm damage to buildings, towers, or antennas. The normal yearly operating expenses for the microwave system figure out to be about as follows:
a. Power costs per year $ 720,00
b. Parts and tube replacement ... 1,200.00
c. Right of Way costs at repeater site 50.00
d. Maintenance and inspection time . 500.00
Total Yearly Operating Cost $2,470.00 51
Future Expansion
The network was originally designed so that it could expand to
incorporate other connecting links, and to perform other services
should the need arise.
The installation of another transmitter at Vineyard Hill and a
receiver at the Eugene Studio would complete a two-way network between
this studio and the rest of the system. When the time comes that a
video tape recorder is available at the Eugene Studio, much more
flexibility of network programing will be available. There can then
be greater diversity in producing and video tape recording of inter-
institutional instructional material.
The production studio at the Oregon College of Education in
Monmouth could be added to the Oregon Educational Television Network
by the addition of a microwave link from that place to the repeater
site at Prospect Hill.
It is not impossible to consider the addition of a third audio
subcarrier between Corvallis and Portland to provide another communication channel. If this were to be done, the present
communication channel could conceivably be used as a circuit for the
interchange of radio programs between the educational radio stations.
Station KOAC in Corvallis and KOAP-FM in Portland are at the present time doing some programing in common, by rebroadcasting the program of the other station. The quality of the transmitted programs could be improved and greater flexibility of operations be given if the stations were interconnected by a microwave network. 52
This type of thinking may be considered as being irrational.
However, the future of microwave communication is just beginning.
It can be expected to perform many new and unusual tasks in the future. VJho can be envious of Aladdin and the power that his lamp possessed? These modern-day "genies," the microwaves, are as wonderful in the power they possess as they stand ready for the call to serve their masters by carrying the loads of modern-day communications. 53
BIBLIOGRAPHY
1. Lenkurt Electric Company. Microwave path engineering considerations. San Carlos, California, 1961. 62p.
2. Presti, Biago. Design considerations in microwave relay studio to transmitter systems. Broadcast Engineering 2:9-31. Mar. 1960.
3. Radio Corporation of America. Microwave equipment and systems planning. Camden, N. J., 1958. 27p.
4. Sarkes-Tarzian Inc. Microwave systems engineering. Bloomington, Ind., n.d. 22p.
5. Sylvania Electric Products Inc. Ferrite devices. Mountain View, California, 1963. 28p. 54
APPENDIX APPENDIX I 55
ELECTRICAL SPECIFICATIONS for MICROWAVE EQUIPMENT
Microwave Relay Transmitter
Frequency Range 5925 to 7125 mc
Power Output 0.7 to 1.3 watt (1.0 average)
Video Input 0.75 to 4.0 volts, peak-to-peak
Video Input Impedance ...... 75 ohms
Amplitude/Frequency Response 60 cycles to 7 mc Flat within 0.5 db
Frequency Deviation ...... 6 mc peak-to-peak
Video Output Impedance* 75 ohms
Video Output Level (nominal)* ... 1.5 volts peak-to-peak
Video Output Polarity* (Sync negative)(same as input)
Differential Gain*
No de-emphasis . . . . . 0.5 db 8 db de-emphasis** ..,. 0.25 db 12 db de-emphasis** . . . . 0.1 db
Differential Phase (3.58 mc)*
No de-emphasis 3° 8 db de-emphasis 1° 12 db de-emphasis . . . .0.3°
Power Supply Requirements (transmitter head and control unit) 117 volts, 50/60 cycles a-c 465 watts
Microwave Relay Receiver
Frequency Range 5925 to 7125 mc
Local Oscillator Frequency .... Transmitter frequency + 130 mc 56
Noise Figure less than 13 db
I-F Center Frequency . . . . . 130 mc
I-F Bandwidth (approx.) .... 30 mc
Discriminator Bandwidth (approx.) . 24 mc
Normal Deviation for 1.5 volts peak-to-peak output ..... 6 mc
Video Outputs (2)1.5 volts, peak-to-peak (1) 0.5 volts, peak-to-peak
Video Polarity Syncnegative
Video Output Impedance 75 ohms
Power Supply Requirements (Receiver and Receiver Control) .... 117 volts, 50/60 cycles, 530 watts
Microwave Relay System
Video Input Level 0.75 to 4 volts; 1 volt nominal
Input Impedance . 75 ohms
Video Output Levels (1) 0.5 volts (2) 1.5 volts
Output Impedance 75 ohms
Differential Gain (linearity)
No de-emphasis . . . . . 0.5 db 8 db de-emphasis . . . . . 0.25 db 12 db de-emphasis . . . . 0.1 db
Differential Phase (at 3.58 mc)
No de-emphasis 3° 8 db de-emphasis 1° 12 db de-emphasis ... .0.3°
Amplitude Frequency Response ... Flat within 0.5 db, 60 cycles to 7 mc 57 Synchronizing Signal Compression ... Negligible
Low Frequency Square Wave Response .. Less than 1% tilt at 60 cycles
*Measured at output of Transmitter Monitor. **Measured at 1 volt peak-to-peak output. APPENDIX II 58
SIGNAL-TO-NOISE CALCULATION
TRANSMISSION FROM Prospect ilill TO Vineyard ,iill PATH LENGTH 1° ll Ml FREQUENCY ?°00 MC
TRANSMITTER. .FT ANTENNA a. REFLECTOR AT . FT k RECEIVER .FT ANTENNA ft. REFLECTOR AT .FT
TRANSMITTER FIELD ANTENNA REFLECTOR SPACE REFLECTOR ANTENNA FIELD RECEIVED CONVERSION S/N RATIO OUTPUT LOSS GAIN LOSS-GAIN LOSS LOSS-GAIN GAIN LOSS CARRIER CONSTANT PP TO RMS DM 06 DB OB DB OB OB OB DIM
30.0
2 -3.0
3 +39.9
4 -1.0
5 -137.5
6 +3.2
7 +36.5
8 -4.0
9 -35.9
10 + 99
II +63.1 Pt "ATX +6AT ±GR "ASL ±GR +GAr -ATX = PR + 99 = S/N RATIO PP TO RMS
ANTENNA GAIN TRANSMITTER POWER OUTPUT
REFLECTOR SIZE GAIN (REF): 0 DBM = 1.0 MILLIWATT 6300MC 7000 MC I .0 WATT = 30.0 DBM 2 FT 29.5 DB 30.5 DB 0.9 WATT = 29.6 DBM 4 FT 35.5 DB 36.5 DB 0.75 WATT = 28.7 DBM 6 FT 39.0 DB 39.9 DB 0.5 WATT = 27.0 DBM 8 FT 41.5 DB 42.3 DB 0.25 WATT = 24.0 DBM 10 FT 43.5 DB 44.2 DB 0. I WATT = 20.0 DBM
FIELD LOSSES
LOSS AMOUNT
PARABOLIC ANTENNAS 1.0 DB/ ANTENNA PASSIVE REFLECTORS 1.0 DB/ REFLECTOR EQUIPMENT LOSSES 1.0 DB/ SYSTEM WAVEGUIDE EXTENSIONS 2.0 DB/ 100 FT FERRITE ISOLATORS 1.0 DB 59
APPENDIX III
MICROWAVE PATH PROFILE DATA from TOPOGRAPHIC MAP
TABLE 1
From Vineyard Hill to Eugene Studio Location Location N. Lat. 44° 38* 25" N. Lat. 44° 02* 50" W. Long. 123° 16* 25" W. Long. 123° 04» 35"
Distance from Elevation above Vineyard Hill Sea Level
0 Miles 1520 Feet 0.1 1240 0.3 750 0.5 550 1.0 300 2.0 300 2.5 450 3.0 250 9.0 230 14.0 245 17.0 280 24.0 300 31.0 350 35.0 380 39.0 400 41.0 410 42.0 420 42.5 440 * 2 ..
< O £&: u H- H- 3 r+ 3 W OQ • < » r+ . H- i~J Ul t_l L.J L_l l_l ImJ L_J L_f •< ftl 3 rooiUiOHOHHOOlCIOBWUijrfWWUMMHHOO 01 3 (-• to 3 ° M f: "•< oiOtnoocnotnocnootnocno-JUiOCnotnowNJoo 0. (t> CO 4r cn en OO * 3 EC Hi a. H- h« *i (-> CO H HQ O 00 sc 0 f- 3 — ^ H> M H N3 N3 t-1 cn en
-3 > to O
s: a
£ET !-0 a> 3 rl- ^ c/: < Ot! • o a> a . CO I-- 01 r+ HlOOlHHUWWO)WMK)IOyi«UN3(i)tn(OOli)M-FU cn H- H "8 KJOOCDOi^lcnoOOl-'OCOOOOCnooOOOOi^Jcn to IO 4r o Hoooocnooooooi-'oooooooooocrio O s: s CO .P r+ < 0 O -d (B 01 K ro H tr O cn H- (B o -4 I-1 H rt < ^ « M
a> co
o as S5 *i
•T3 O ?sr a H$ h- 3 r+ o W OQ • T1 CO r+ • 1 13 fa o mfjrwWMOlflfflM^OlOlUIUIfWWHOFMOaJ-J-JOICIlOl-FfWaMMHHQ (B 3 M CO o o N3 -p *o ocnocnoooooocnmooiocngnooooooocnocnoocnocnocnocnocno h- a CO -p fl> cn O 0 o EC Hj ri (-.. H o cn *-• s -J H1 se a H« 3 «• «• I-*
o> oo
5 r+ O
S1 HT 0> 3 rt CO < m » •n <8 BJ . o !-• ftl rt i HHHHMMMMHHHN*OtN)ComO>0) *-• H- t-> r+ focnoocncooenoocn-jcn^jhoocno© M^UN!NVIOOU1MMOON)WM«)>JW NJ N> -P t- CnoOOOOOOOOOCnOcncnoOOO cncnt-'vicnoooocncnoocnocnocncn H< r§ N3 cn 0> < o o 3 ^n (D BJ a (8 H> tr •P N3 a o M IO rt < «. ~ 0 •P N> cn cn 62
TABLE 3, Continued
Distance from Elevation above Prospect Hill Sea Level • •mwniii.inMii^HWM—0m • uniim nwirii
H5.5 Miles 600 Feet 46.0 500 46.5 450 47.0 450 47.5 600 48.0 400 43.5 600 43.0 1043 63
APPENDIX IV
COST ANALYSIS OF MICROWAVE SYSTEM
OREGON EDUCATIONAL TELEVISION MICROWAVE NETWORK
Initial equipment cost Motorola $ 42,000 RCA 18,000 $ 60,000
Added equipment since original installation sub-carrier equipment, power supplies, and amplifiers 4,065
Engineering and installation costs .... 3,200
$ 67,265
Estimated yearly operating costs $ 2,470
QUOTATION BY PACIFIC NORTHWEST BELL ON MONTHLY CHARGES FOR DUPLICATING SERVICE WHICH OREGON EDUCATIONAL TELEVISION MICROWAVE NETWORK PRESENTLY SUPPLIES - MARCH 23, 1963
Simultaneous 2 way video transmission Portland - Corvallis $ 4,000.00
One way video transmission Eugene to Vineyard Hill .... 1,100.00
One 2 way audio circuit between Portland and Corvallis .... 247.75
Total monthly rental charge for service $ 5,347.75
The cost for one year service would be $ 64,173,00 APPENDIX V
64 FREQUENCY RESPONSE OF MICROWAVE SYSTEM from PORTLAND TO VINEYARD HILL
The input signal was held constant at the input to the modulation amplifier while the response was read from a vacuum tube voltmeter at the receiver IF strip output, (no filter, pre-emp or phase compensator nets included)
OUTPUT LEVEL REFERENCE TO FREQUENCY db 0 db at 1 kc
100 cycles 10.2 db t 0.2 db 200 10.2 + 0.2 500 10.0 0 750 10.0 0 1000 10.0 0 3000 10.0 0
10 kc 9.8 - 0.2 30 10.0 0 70 10.0 0
100 9.9 - 0.1
300 9.8 - 0.2
700 9.7 - 0.3
1.0 mc 9.5 - 0.5
1.5 9.5 - 0.5
2.0 9.6 - 0.4
3.0 9.5 - 0.5
4.0 8.5 - 1.5
5.0 7.0 - 3.0
5.5 6.6 - 3.4
6.0 5.6 - 4.4
6.5 4.0 - 6.0
6.8 2.5 - 7.5
7.0 1.5 - 8.5
7.1 0.75 - 9.25
7.5 - 1.5 -.LI. 5
Data taken November 27, 1962 by:
Len Thomas, Motorola Field Engineer Ben J. Ballard, Chief Engineer KOAC-TV 65
APPENDIX VI
AUDIO FREQUENCY RESPONSE OF MICROWAVE SYSTEM from EUGENE AND CORVALLIS TO VINEYARD HILL
The input signal to the audio console was held constant while the receiver output level was read on a vacuum tube voltmeter.
EUGENE RECEIVER CORVALLIS RECEIVER FREQUENC.Y OUTPUT OUTPUT
«. 30 cycles 4.5 mm 2.6
50 - 3.5 - 1.8
100 - 2.7 - 1.0
400 - 1.0 - 0.5 1000 0 0 3000 + 1.3 + 1.5 5000 + 1.5 + 1.8 7500 + 1.2 + 1.8 9000 + 1.0 + 1.8 10000 + 0.5 + 1.8 12000 + 0.5 + 1.8 13000 + 0,5 + 2.0
15000 - 3.0 + 1.0
Data taken March 21, 1963 by:
E. E. Manning, KOAC-TV Technician Ben J. Ballard, Chief Engineer KOAC-TV