Submitted December 17, 1998
Iowa Space Grant Consortium
William J. Byrd, Director
Address: 408 Town Engr.
Ames, IA 50011
Project Advisor: Dr. John
Professor, Department of Electrical and Computer Engineering
Office Address: 333
Ames, IA 50011
|Eric K. Davis||422 Stonehaven Dr. Apt. 18
Ames IA 50010
|Rod Schmidt||422 Stonehaven Dr. Apt. 18
Ames IA 50010
|Brice Jensen||3430 Woodland St.
Ames IA 50014
|Josh Krapfl||331 Hillcrest St.
Ames, IA 50014
|Eric Marsh||225 N Hyland #10
Ames, IA 50014
|Maung-Aung Kyaw-Phyo||246 N Hyland Ave. #106
Ames, IA 50014
|Sun Kyu Park||2001 Prairie View W #302
Ames, IA 50011
|Wan-hor Looi|| 2717 West St. #3
Ames, IA 50014
Receiver Calculations *
Analysis of Ultra Cyber *
Receiver Design *
PCB board fabrication *
Connector used *
The low noise amplifier (LNA) *
Micro-strip bandpass filter *
Down converting part *
Antenna Calculations *
RECOMMENDATIONS FOR FUTURE WORK *
The focus of this team is the continued restoration of the 8.5-meter
dish at the Fick Observatory south of Boone, IA. This will include the
receiver system design, testing, and calibration along with completion
of the control system. Included in this report is a discussion of the design
objectives and the proposed technical solution as well as the actual technical
The 8.5-meter parabolic dish antenna located at the Fick Observatory
has been funded to be brought back into operation as a radio telescope.
The Iowa Space Grant Consortium has challenged the senior design team to
restore the dish that has been dormant for nearly fifteen years. This included
reworking the gearboxes, cleaning and painting the dish and mount, and
replacing the existing coaxial cable. With mechanical details out of the
way, the research and design of the receiving system will begin.
The increase in funding and research of radio astronomy has increased
the popularity among scientists around the world. The Search for Extraterrestrial
Intelligence (SETI) has also struck a common base in radio astronomy. With
this project, it is our hope to construct a radio telescope with the existing
equipment and additional equipment of our own design. This radio telescope
will allow scientists and researchers to continue science and exploration
of space in the radio frequencies.
TECHNICAL SOLUTION AND ACHIEVEMENTS
The technical solution is broken down into two main tasks with subtasks
applied as needed. To date, the two tasks include the control task and
the receive task. Following is a discussion of technical achievements for
each main task and their subtasks.
The purpose of the control task is to provide for an accurate and user-friendly way to position the dish. It is important to know the precise position of the dish in the sky so the user can determine where to position the dish using astronomical quantities. From here the control task will be broken down into two main subtasks that are the mechanical subtask and the software subtask.
The antenna is mounted on a five-inch naval gun mount converted specifically
for an application in positioning a large parabolic reflector dish. This
mount is positioned on top of a fifteen-foot tower. These gun mounts are
commonly converted for antenna positioning. The mount is positioned with
hand cranks or electric motors, both of which are connected to a gearbox.
The mounts were not used or maintained for several years therefore were
not functional at the beginning of the project. This past summer the gearboxes
and motors were removed and reconditioned. Many of the gaskets used to
seal the gearboxes had deteriorated and the grease had leaked out, allowing
moisture to enter and rust the gears. The restoration included a complete
disassembly and overhaul of both gearboxes. The overhaul process included
resealing with new gaskets and grease. The amount of reconditioning required
for the gearboxes took several hundred hours to complete. Mechanical restoration
was by far the most difficult task.
The final objective of the control system is to point the antenna at
a stationary source in space and track the source for a specific amount
of time. In order to accomplish this objective, a simple block diagram
of the control system was developed. The control system block diagram is
shown in Figure 1. This block diagram shows the main components of the
control system including the motion control card, the motors, motor drivers,
and the shaft angle encoders. Each of these components will be discussed
in depth in the following paragraphs. To develop this block diagram it
was necessary to determine what needed to be done in order for the antenna
to be able to track a stationary source. The section following the block
diagram will discuss initial design ideas for control of the antenna.
Figure 1: Block diagram of control system
INITIAL DESIGN IDEAS
The control of the dish and the mount were the first topics chosen for
the control group. Following are initial ideas that the group came up with.
Motion Control Card
The motion control card being used for this project is Motion Engineering
Inc. LC/DSP motion controller. This card had already been purchased
by a past project group, but was never used. Rather than purchasing a new
motion control card, the control system was designed around the motion
control card that was already available.
The card itself consists of an Analog Devices 40MHz ADSP-2105
DSP chip for on-board computing. After the firmware is loaded and an interrupt
is generated, the DSP constantly executes a series of events as follows:
Only going through this loop when an interrupt is generated allows the
control card to work in a real time environment.
In order to interface the card with the control system, Motion Engineering
Incorporated (MEI) has developed an interface module and ribbon cable.
The interface module is called an STC-50, and consists of one 50-pin interface
with screw down terminals to connect wires coming from the encoders and
going to the motors. It is possible to control two axes using one of these
STC-50s. The ribbon cable is a MEI CBL-100 ribbon cable, and it consists
of a 100-pin connector on the controller card end. It then splits into
two parallel ribbons with 50 pin connectors at the end of each to interface
with two STC-50s. This allows for control of four separate axes simultaneously
in one system.
The card operates in either an open-loop or closed-loop
mode as shown in a figure to be included at a later date. The mode depends
on whether or not there is an encoder present to send feedback to the card.
For this project, two of the four axes available on the control card will
be used. One axis will be used to control azimuth, while the other will
be used to control elevation. Since shaft angle encoders will be used for
each axis, the closed-loop system will be used. In the closed-loop system,
signals from the encoder are sent to the control card. The card then interprets
them and signals are sent to the motors telling them exactly what to do.
The interpretation of the signals is done through software that will be
written and tested. Most of the software has already been developed in
sample C programs that came with the motion control card. The rest of the
software will be developed throughout the course of this project.
We differentiated between two types of encoders and it was found that
incremental encoders are used for speed and angle of rotation measurements,
and absolute encoders are used for exact position recognition (angle position
encoder). For our project absolute encoders and an inclinometer were found
to be the most feasible to use in encoding azimuth and inclination of the
antenna dish. In this report we have included the approximate resolution
needed for both inclination and the azimuth encoders. We have done research
on the absolute encoder and how its input and output can be interfaced
with our existing controller card.
With the approximate calculation of the half power beam width to be
around 1° we have estimated the resolution
of the absolute encoder and the inclinometer to be following:
Taking 1/10 of the half power beam width:
With absolute encoders, the angular position is readable as digital
information on the rotary disk. The exact position is hereby available
as a digital bit-pattern as soon as the equipment is switched on. The exact
position is also known after a power failure or when the critical frequency
is exceeded. The disk is separated into different tracks that are read
by an optical sensor. The values are digitized and can be accessed as coded
outputs. The single step Gray Code is most popular. Only one code-information
is changed per measurement-step, and it is thereby relatively simple to
control for data-transfer errors. The Binary and Binary Coded Decimal (BCD)
-Codes are also used. The following figure will show how the interface
module from the controller card links to the encoder. The figure is not
yet included in this document.
While it was determined that absolute encoders would have been the best choice for our project, upon further research we decided to implement potentiometers for the time being. Absolute encoders offer greater accuracy and reliability, but to decode their output and calibrate them would take more time and programming than we could afford for such a large project. It was decided to use potentiometers for the time being until we get a completely working system. The analog signal from the potentiometers is compatible with our input/output card and software, so it is basically a matter of placing the potentiometers on the dish and wiring them up. These will work just fine for initial readings and testing, but future senior design teams will probably want to modify our software and control system to accept absolute encoders.
Input and Output Signals
The following are the input signals from the absolute encoders: A(0), A(1), B(0), B(1), INDEX(0), and INDEX(1). Each input signal has two channels that output the same signals. For example, A(0) has A(0+) and A(0-). The purpose of using two channels is if the encoder signals are to transmit a long range the differential output can be taken from (-) and (+) channels of the same signal so that the noise will be canceled out. This is important for our project since the encoder has to relay the signal from the antenna to the PC in the control room that is approximately 80 feet away.
will supply a voltage to the software and the software will interpret the
position of the dish based on this voltage. One potentiometer will be used
for each axis, elevation and azimuth. Since potentiometers are subject
to variations in resistance with changing weather conditions and temperatures,
we will want to calibrate the software to the potentiometers each time
the system is used. This problem will be avoided when absolute encoders
are implemented. To help reduce the problems caused by variations in resistance,
the potentiometers will be supplied from a constant current source. A differential
amplifier will be used to compare the received value from the potentiometers
with the value supplied to them by the constant current source.
To calibrate the potentiometers, and to eliminate the risk of destroying
gears, we will also implement limit switches for the four dish direction
limits, elevation minimum, elevation maximum, azimuth minimum, and azimuth
maximum. To calibrate the elevation potentiometer, we will move the dish
to the full elevation minimum position. When the dish reaches this position,
a limit switch will be opened and the motors will stop. At this point,
the limit switch circuitry will send a digital elevation minimum signal
to the software so that it knows the elevation minimum position has been
reached. The software will take a reading from the potentiometer and the
software as the elevation minimum value will store the reading. The dish
will then be rotated to the elevation maximum position where the elevation
maximum limit switch is opened. Again the limit switch circuitry will disable
the motor and send a maximum elevation digital signal to the software.
The software will take another reading from the potentiometer and store
this value as the elevation maximum position. A similar process
will be used to calculate the azimuth minimum and maximum readings.
Limit Switch Circuitry
The limit switch circuitry was designed by the control group to fit
our specific needs. It will be used not only for calibration purposes,
but also to disable the motors when a axis limit is reached to prevent
damage to the gears or motors. All four limit switches are wired as a normally
closed switch. Using a normally closed configuration helps prevent a malfunction
in the event that a wire breaks. When a limit switch is activated, the
corresponding motor circuit is opened and the motor is disabled. At the
same time, a digital signal is sent to the software alerting it of which
limit has been reached. This signal is used to set a flag in the software
to warn it that the motor direction for that axis has to be reversed. The
circuit also receives input from the software as to which direction the
motor is being instructed to move. If the software is still attempting
to move the motor in the same direction it was rotating when the limit
switch was contacted, the motor will stay disengaged. When the software
sends a signal to the motor control card to reverse the motor direction,
the motor is again enabled and the dish moves away from the limit switch.
Disabling the motors is accomplished using the ENABLE connections on the
KBRG-212D Motor Control Cards. When these connections have continuity,
the motor output is enabled. If the connections lose continuity, the motor
output is disabled. The limit switch circuit controls this ENABLE connection
through the use of MOS relays, which also provide electrical isolation
between the limit switch circuit and the motor control cards.
The mount requires precise controls and very little backlash to maintain
the needed accuracy. The previous motors are 230 VDC, 1.5 HP electric motors.
One is for azimuth control and the other is for elevation control. The
motors are identical although the gearing is different so the output revolutions
We differentiated between two viable methods to drive the antenna. The
first is to use the existing motors, which have been repaired and rebuilt.
The second is to mount fractional horsepower motors on top of the control
brackets, put a sprocket on the hand crank shaft, and link the motor shaft
to hand crank shaft with a chain. Both methods have been used before. In
either case, reversible motors would be needed to point the antenna at
a stationary source in space and track the source for specific amount of
time. A maximum speed, or slew rate, is 0.7 °
/minute. This occurs mostly in the azimuth direction when the source is
at its highest elevation in the sky. The minimum slew rate is 0.1°
There are two methods for tracking a source. The first is to continuously
track in real time. This would require variable speed DC motors and speed
controls. The second is to use a start-stop type of tracking. The latter
method could be achieved with AC or DC motors. The antenna position would
be updated more often as the source moves faster and less often as it moves
slower. The start-stop method is much more viable if the antenna gain is
found to have a lower efficiency. Both methods would require geared motors
or gear reducers to attain lower rpm values and more torque.
For our project, stepper motors were found to be the most feasible in
positioning azimuth and elevation of the antenna because a stepper motor
is much easier to control by a PC than is a DC motor. In this report we
have done research on the stepper motors and their drives as well as how
its input can be interfaced with our existing MEI LC/DSP motion controller
Stepper motors can be viewed as electric motors without commutators.
Typically, all windings in the motor are part of the stator, and the rotor
is either a permanent magnetic or, in the case of variable reluctance motors,
a toothed block of some magnetically soft material. All of the commutation
must be handled externally by the motor controller. The motors and controllers
are designed so that the motor may be held in any fixed position as well
as being rotated one way or the other. Stepper motors translate digital
switching sequences into motion. Unlike ordinary DC motors, which spin
freely when power is applied, stepper motors require that their power source
be continuously pulsed in specific patterns. These patterns, or step sequences,
determine the speed and direction of a stepper motor’s motion. For each
pulse or step input, the stepper motor rotates a fixed angular increment.
Typically this step is 1.8 or 7.5 degrees.
A stepping motor controller should provide two bits of output to control
the motor, one bit indicating the direction of rotation and another bit
that is pulsed every time the motor is to be stepped. The software to operate
such a motor controller is simpler than the software to directly control
the current through the motor windings. Many microprocessor-based stepper
drivers use four output bits to generate the stepping sequence. Each bit
drives a power transistor that switches on the appropriate stepper coil.
The stepping sequence would be stored in a lookup table and read out to
the driver lines as required.
The following are the input signals to a stepper drive from the LC/DSP
STEP+/- and DIRECTION+/-
For motor signals, the maximum output from the controller is 7 V and
40 mA. DSP controllers synchronize the direction pulse with the falling
edge of step pulse output. This ensures that a step pulse and direction
change will never occur at the same time.
Stepper motors were chosen for this application for several reasons.
First, for motion control with stepper motors, open-loop control is possible,
which negates a need for feedback. It would be much easier to control the
position of the antenna with a configuration like this. Second, the motion
control card we already own is capable of controlling stepper motors. These
factors helped us choose stepper motors for this system even though they
are more expensive than conventional DC motors.
After discussion and further research on stepper motors, it was later
decided that we should stay with the original motors that came with the
gun mount. The motors had already been rebuilt, and they were obviously
compatible with the positioning system. Using these motors and gearing
gave us additional time to work on other aspects of the project. To control
these motors, we needed more industrial motor control cards. The existing
motors are large DC motors as stated above and the current motor control
cards wouldn’t be able to operate them. KB Industries makes an SCR-based
motor control card that is perfect for our application, so we went with
the KBRG-212D Motor Control Card. This motor control card has other
advantages as well. As mentioned in the Limit Switch
Circuit section, these cards have an ENABLE connection, which
allows easy interface to the control circuitry for safety measures. These
motor control cards also allow for motor voltage control or motor current
control. With either setup, limits can be placed on the maximum allowable
amplitude. This feature can help ensure that in the event of a malfunction,
the dish will not move extremely fast or produce enough torque to strip
The next subtask to the control is how to make the system work with
a user-friendly interface, as well as keeping the complexity of the software
programming to a minimum. Following are some of the control topics that
were discussed when preparing to start the software design.
One of the main ideas considered was the fact that the source would
not move, but the antenna would because the earth is constantly moving.
Since standard time does not apply to objects in space, it was necessary
to convert standard time into sidereal time. This is not an easy task because
there is no standard conversion method between standard time and sidereal
time since the sidereal day varies due to the time of year and other factors.
As a result, it was determined that it would either be necessary to purchase
a sidereal clock that can be interfaced with our control system, or to
maintain a sidereal clock through software. An extensive web search has
shown that the best thing to do for this is to go with the software option.
This is because sidereal clocks are relatively difficult to find, and the
few that are commercially available do not readily interface with our control
system. There are many software versions of sidereal clocks found on the
web that we can use for our purposes. Many of these clocks even have the
source code readily available, so it will be a fairly simple task to incorporate
this source code into our control system software.
We have decided to use the Microsoft C/C++ compiler since our controller
card operates in C language. We considered the use of two software packages
from National Instruments for our GUI (Graphical User Interface): LABVIEW
and LABWIN. Our initial research found that it is possible to use LABWIN
since it can interface the controller card via a C program. On the other
hand, if LABVIEW is used we will need extra interfacing and drivers to
allow it to communicate with a GPIB (General Purpose Interface Bus), which
are used by LABVIEW. After further research, it was discovered that LABVIEW
is used for motion control applications, and will work quite well for both
the receiver and control systems with the purchase of a data acquisition
The first step in implementing a quality control system is to ensure
that the component that links all of the other components together will
be powerful enough to handle all of the sending and receiving of signals.
This leads into two of the most important components of the control system:
the computer and the I/O card.
In choosing a PC, the only real factor to be considered was that the
end goal of the project is to do real-time tracking of a source in space.
Another PC consideration was that PC costs are at an all time low, so it
was necessary to also consider future projects and their computing needs.
The PC was upgraded with the following components:
The first reason the PCI 1200 was chosen was because it can handle
all of the signals that need to be input to the computer and output from
the computer. These signals include:
The card has eight analog input lines, two analog output lines, and
twenty-four bi-directional digital lines, so it could easily handle all
of the necessary signals for the system.
Another major consideration for the I/O card was the precision of the
signals being input to the computer. A resolution of 3600 units is necessary
for reading the positions from the potentiometers. The PCI 1200
has a 12-bit ADC, which allows for a resolution of up to 4096. This is
perfect for the control system.
The final consideration had to do with the software. It was necessary
to choose software that would allow for easy programming in a limited amount
of time. National Instruments LabView was selected as the software development
package because it is designed for automation. Its graphical interface
allows for fast, easy development of useable software. Taking LabView into
consideration, a National Instruments I/O card made sense because it would
be readily compatible with the LabView software.
Now that the PC and I/O card are selected, the next step is to develop
the software that would link all of the control components together. The
specific software package selected for this application is the LabView
Student Edition because it contains all of the functionality necessary
to complete the application without the high cost of the full version of
Before the software could actually be written, several values had to
be calculated in order for the signals within the control system to be
within certain ranges. The first value that needed to be calculated was
the value of the position of the dish. This was necessary in order to convert
the analog signal sent from the potentiometers into a value representing
the position of the dish in degrees. This calculation is done using a simple
linear relationship between the analog (+5 to –5) signal and a position
value (0 to 360 degrees in Azimuth or 0 to 86.5 degrees in elevation).
The equation to be used is:
AP = m * AV + b (1)
Where: AP is the actual position in degrees
AV is the actual voltage sent by the potentiometer
b is the intercept of the linear relationship
The other value necessary to complete the software is the signal that
is sent to the motor control cards. This signal must be an analog signal
between +5 and –5 volts that is dependent on the difference between the
actual and desired position values. This signal will control the speed
of the motor. When the actual position of the dish is equal to the desired
position of the dish, the signal sent to the motor control cards in theory
should be equal to zero.
In this equation, G is the value that must be calculated.
This is done as follows:
Now that these values are known, the software can be written. Using
LabView, the first step in implementing the software is to read a voltage
through the I/O card. This is done using a DAQ virtual instrument that
is provided by LabView. A virtual instrument (VI) is part of a program
designed using LabView that has a specific functionality. LabView has several
VI’s that will be used by this control system. The first VI used is one
that reads an analog voltage from a specific line on the I/O card. This
VI is then connected to a formula node containing the formula to convert
a voltage to position in degrees. The position value is then connected
to a numeric indicator for display on the screen. Then a numeric control
is placed on the front panel so the user can input a desired position.
The desired position is compared to the actual position and the output
is connected to another formula node that outputs the motor control signal.
The final part is a WHILE loop that allows the program to continue as long
as the actual position does not equal the desired position. When the two
position values are equal, the loop will stop.
The next step in writing the software is to copy the above steps for
the other part of the control system (either azimuth or elevation). Once
this is done, everything written is enclosed in one giant WHILE loop that
will continue until both of the inner WHILE loops has terminated.
After this is completed, the last step in developing the software is
to initialize the dish to account for temperature and other factors that
will affect the voltages sent by the potentiometers and to ensure that
the actual position of the dish with respect to the celestial object is
known. To do this, LabView’s sequence functions are utilized. In
the first frame, the dish moves until the limit switches for the higher
limits (86.5 and 360 degrees) are set. Then the voltage signals from the
potentiometers are stored and the second frame is implemented. In this
frame, the dish moves to the lower limits and the voltages are stored again.
Then, the values calculated above are recalculated using the new voltages
at the limits. The dish will then be at its zero position and it can continue
operating as described above. Once this is complete, the software for the
control system is fully implemented and testing of the system can be performed.
The heart of a radio telescope is the receiver. The following section
will discuss receiver fundamentals.
The radio telescope employs the superheterodyne receiver technique to
extract the source information from the received unmodulated signal that
may be corrupted by noise. This technique consists of both up-converting
and down-converting the input radio frequency band signal (1GHz - 1.8GHz)
to an intermediate frequency (IF) band signal (200MHz - 40MHz), and then
extracting the signal by using the quadrature product detector.
In converting the radio frequency band into the intermediate frequency
band, we apply two similar stages of processing with a tunable voltage
controlled oscillator, IF filter, and IF amplifier in each stage. The first
stage is for coarse tuning, in which a 1000MHz - 2000MHz tunable voltage
controlled oscillator (VCO) is selected to phase shift the signal. Through
the IF filter and IF amplifier, the signal is lowered from 1.4GHz to 200MHz.
The second stage is for fine-tuning, in which a 220MHz - 260MHz tunable
VCO is selected to process the signal together with another IF filter and
IF amplifier, producing a signal with a frequency of 40MHz. Through the
two stages, we can effectively filter off the noise and the unwanted image
Note: The image response is the reception of an unwanted
signal located at the image frequency due to insufficient attenuation of
the image signal by the RF amplifier.
By using the quadrature product detector, the signal is then recovered
and sampled into two digital signals, which are known as Binary Phase Shift
Keying (BPSK) signals, for computer input; BPSK technique is used for optimum
digital-signal-detection. Generally, low pass filters are used for recovery,
and analog-to-digital converters are used for digitizing the signal. Then,
through the computer Digital-Signal-Processing (DSP) software, a square
law detector is implemented which makes the receive signal proportional
to power for analysis.
The main advantage of employing the superheterodyne receiver is that
extraordinarily high gain can be obtained without instability. The stray
coupling between the output of the receiver and the input does not cause
oscillation because the gain is obtained in disjoint frequency bands –
RF, IF, and baseband. The receiver is easily tunable to another frequency
by changing the frequency of the local oscillator signal and by tuning
the bandpass of the RF amplifier to the desired frequency.
Following are some of the calculations that are involved in designing
a receiver. This project has been started with the purchase of a commercial
receiver in care of time. There is also a receiver that has been designed
by a third party that is being built and tested in parallel with the project.
In the future it is possible that senior design teams can design receivers
for use with the dish given the proper numbers needed for design.
Table 1 shows the specific information of our components:
|1) Pre-select Filter||
|2) Low Noise Amplifier||
|4) 1st IF Filter||
|5) 1st IF Amplifier||
|6) 2nd IF Filter||
|7) 2nd IF Amplifier||
|8) Low Pass Filters||
Table 1. Receiver Component Specifications
To determine the gain of the receiver system:
Gain of the system (dB) = Gain of receiver (dB) + Gain of antenna (dB)
The gain of the receiver equals to the total gain of the components.
Determine the Noise Temperature & Noise Figure of
(Excluding Cables & Filters). The equations and values are shown
in Table 2.
G = 10+e(dB/10)
|1) Low Noise Amplifier||
||G1 = 316.23||
||G2 = 6.31||
|3) 1st IF Amplifier||
||G3 = 1995.26||
||G4 = 6.31||
|5) 2nd IF Amplifier||
||G5 = 100000||
||G6 = 6.31||
Table 2. Gain and noise calculations
Noise factor (FN) of part of the receiver system is the ratio
of the output noise power to the input noise power.
Noise figure (NF) is a figure of merit that measures the receiver’s departure from the ideal state. NF is often expressed in decibels, dB.
FN is the Noise factor
Noise temperature is a means for specifying the noise in terms of an
equivalent temperature (Carr 44). Noise temperature is often abbreviated
Te. It is also important to know that this is not the physical
temperature of the amplifier.
An equation relating the noise temperature to noise factor follows:
Te is the Noise Temperature
FN is the noise factor
T0 is 290K
Relating noise temperature to noise figure is as follows:
Te is the noise temperature
k is the antenna efficiency, usually around 55%
N.F. is the noise figure.
A more rigorous noise temperature analysis can be found in Kraus 7-22.
Find the noise temperature of the receiver:
NF is the noise figure
Analysis of Ultra
Analysis of the UC Receiver will take place during Winter break 1998.
Following are technical specifications that exist at this time. Also included
are some pictures of the receiver itself.
Specifications for ULTRA CYBER Radio Astronomy System
ULTRA CYBER System Specifications:
Tuning: Choke, available
Output: Matched to LNA
Bandwith (BW): 100 MHz
Noise Figure (NF): 0.37 dB
Noise Temp: 26 degrees Kelvin
Gain: 28 dB
Power Requirements: 15 Vdc @ .1 Amps.
Bandwidth ( 3dB ): 25 MHz
Noise Figure: 1 dB (Approx.)
Gain: 60 dB
Image Rejection: > 50 dB
Mixer Oscillator: Crystal Controlled/PLL
First IF: 407 MHz
Second IF: 70 MHz
Power Requirements: 15 Vdc @ .25 Amps
ULTRA CYBER System: Computer Controlled
Software: BASIC ( DOS )
Interface: Serial RS 232
IF: 70 MHz
Bandwidth: 25 MHz
Max Gain (System): 100 dB
Digitalization: 12 Bit A/D Converter
Extra Digitizer: 0 - 5 Vdc
Audio Detection: Diode Rectifier
Output: Audio amplifier ( not provided )
Power Requirement: 110 VAC US or 240 VAC European
Converter: Cast Aluminum Chassis/Painted
Backend: Rack/Table mount
Figure 2: Pictured here are the receiver backend, LNA, Convertor, and Feedhorn
Figure 3: Pictured here is the back side of the backend of the receiver
Along with the purchase, analysis, and installation of the Ultra Cyber
system, a student-designed receiver is being built in parallel with the
PCB board fabrication
Printing copy and reversing film
This stage allows us to copy artwork directly from a magazine or book
utilizing a plain paper photocopier. Users may also use a laser printer
to output their CAD artwork directly onto the film media. Once the copy
from the photocopier or laser printer is available, a contact reversal
is easily made with the reversing film.
Exposing the photo-resist
Dry film resist is a negative acting photo-resist copper clad. Areas
of the resist exposed to ultraviolet light through the clear areas of the
negative artwork are hardened and will not be removed in the developing
solution. Areas that have been exposed to the ultra violet light darken
in color and a latent image is visible. The photo-resist protected by the
opaque areas of the negative is therefore not struck by ultra violet light
and will not be dissolved in the developing solution.
We use a sodium carbonate solution to develop the copper panel. In this
process, the unexposed copper will be washed away, and will leave the hardened
exposed copper in the shape of the artwork from the negative film.
In this stage, etchant (ferro chloride) solution is used to wash off the copper from the developing process. Etchant is an acidic chemical which may cause severe damage if handled or used improperly. The used etchant is sent to the recycle center.
Almost the same stage as developing process. The same chemical is used
to isolate the etchant from the artwork formed copper.
Providing the circuit is easily soldered, a layer of tin should to be
coated on the circuit. Tin is less likely to oxidize than copper. The PCB
can be used longer if it is properly tin-plated.
In this step, we follow the test circuit of a certain component from
the company website and drill corresponding holes on the PCB. The advantage
of this is to reduce the noise temperature produced by the PCB, so that
a higher quality PCB is produced.
IIP3 is the input third order intercept point. It is a measure of the
distortion performance of the system. Third harmonic distortion (THD) can
be measured using a distortion analyzer. The formula representing the THD
The following micro-strip filter design was tested in the computer simulation
and has the following specification:
Frequency range from 1296 - 1660MHz
Rin = Rout = 50ohms
Thickness = 0.062" Width = 0.094
Width/Height = 1.52
0.5oz. double copper tin/lead plated.
The characteristic impedance:
The w/d of the micro-strip filter is greater than 1, then:
Down converting part
The schematic of the LO is shown below:
The schematic of the receive converter is shown below:
The reflector antenna is constructed with a main reflector and a subreflector,
also known as a Cassegrain Feed Antenna. The surface of the main reflector
is made of aluminum mesh, which is in excellent condition, and free of
deformities. The mesh is small enough so that it is effective for the range
of wavelengths we will be receiving. The subreflector is also small enough
in diameter with respect to the main reflector that it will not significantly
hurt the gain of the antenna because of the ‘shading effect.’ At this time,
the feedhorn and rigid coaxial cable have not been tested or measured to
see if they will be effective for our application. From observation and
discussion, it is assumed that they will work for the required range of
frequencies, but it is not known if they are efficient enough. If they
do not meet our specifications, a new feedhorn will have to be designed
and built with the help of Dr. Stephenson, who has offered his assistance.
The rigid coax between the tower and the building also needs to be tested
with a network analyzer to see if it meets specifications. If not, Andrews
Heliax semi-rigid coax will be purchased to fill this need.
The gain equation of a parabolic antenna:
G is the directional antenna gain
l is the wavelength
D is the diameter
k is the reflection coefficient (0.4 to 0.7, 0.55 most common)
Radius of the antenna:
l = 3e8 / 1.42e9
l = 0.211267m
Gain of our antenna:
f = The Frequency that we are observing
l = The wave length
According to Maxwell's equations, c = l f.
To determine the frequency the wave guide on the antenna is designed
to accept, we have approximated the wave guide diameter to be at 11" with
an error possibility of 1".
\ since c = l
f Þ f = c/l
For a conversion factor, 1 meter = 39.37 inches was used.
\ with the 11" estimate, we obtained .2794
Because the wave guide must be at least 1/2 the wave length, l = 2 * .2794 m = .5588 m.
\ f = (2.998 * 108 m/s) / (.5588
m) = 536.5 MHz.
To find the error, at 10" we obtained .254 m Þ
l = .508 m.
Then at 10", f = 590.2 MHz
For the error at 12" = .3048 m Þ l
= .6096 m.
\ the wave guide is designed for 536.5 MHz
± 54 MHz.
To check the area for other radio interference, we plan on designing
a small wave guide as a filter. The specifications of that guide will be
5 3/4 " copper pipe with a copper horn extending
to 7" in diameter. The copper pipe section will be 2' in length. This will
block all frequencies less than f = 1.026 GHz ±
.001 GHz. One of our options is to put a smaller insert in that guide to
help keep cellular communications from hurting our system, and not having
to add a filter that will add more noise too soon in the system.
As mentioned before, the mount will be repaired mechanically this summer.
In addition, due to the poor appearance of the structure, the mount will
be cleaned and repainted this summer. From not being maintained for many
years, an area of trees and brush that has grown beneath the structure
Control of the radio telescope will occur from a PC located in the control
room. The back end of the receiver system will also be located in the control
room. So, an area needs to be cleared in the control room for this equipment,
and all components will be mounted in a rack or possibly a stable environment
RECOMMENDATIONS FOR FUTURE
In the future, it would be highly recommended to upgrade the dish position
feedback system. The current implementation using 10-turn potentiometers
has a limited service life. Absolute encoders would provide for much more
accuracy, and would eliminate the need for calibration every time the system
is used. This would benefit other future modifications such as completing
a network connection method to control the dish from a remote location.
The position calibration process is fairly time-consuming. That time could
be more effectively utilized taking readings, especially since the dish
would likely get much more use if it were available via remote access.
The ability to track known sources is another goal for future groups.
With the tracking software in the works, only minor software modifications
and additions would be required to enable this feature. This process would
require extensive research and algorithm manipulation to properly implement
As for the receiver, future work would include implementing another receiver. The current receiver will also need work. This work would include receiver calibration.
There will be several issues addressed next semester that will be included in this future work section.