Client:         Iowa Space Grant Consortium
                    William J. Byrd, Director

Address:     408 Town Engr. Bld.
                    Ames, IA 50011
                    Phone: 515-294-3106

Fax:             515-294-3262

 E-MAIL: wbyrd@iastate.edu

Project Advisor:     Dr. John P. Basart
                                    Professor, Department of Electrical and Computer Engineering

Office Address:      333 Durham, ISU
                                    Ames, IA 50011
                                    Phone: 515-294-4955

E-MAIL: jpbasart@iastate.edu

RECEIVER *
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 *
Antenna Calculations *
Miscellaneous *
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 solution.
 
 

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.
 
 

1. Restore the antenna mount to working mechanical condition.
2. Implement a system that can control the movement and positioning of the antenna.
3. Implement a commercial receiver.
4. Design a wide bandwidth receiving system that will receive signals in the range of 1.0-1.8 GHz, specifically the hydrogen spectral line at 1.42 GHz.
5. Integrate the entire system so a computer in the control room can control it.
6. Produce proper documentation so the radio telescope may be altered or improved through future senior design projects.

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.
 
 

Control

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.

Mechanical

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.
 
 
 
 

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:
 
 

1. Read all encoders
2. Read analog and parallel input
3. Calculate next trajectory point
4. Check for event triggers
5. Perform event action
6. Calculate and set DAC output
7. Go to next axis and repeat
8. Exit from interrupt

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.
 
 

Shaft Angle Encoders
 
 

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:

1. Steps needed by Azimuth encoder for 360° = 360/0.1= 3600
2. The resolution of the encoder =1/3600=0.00028°
3. Steps needed by encoder for 90° = 90/0.1 = 900
4. The resolution of the inclinometer =1/900=0.0011°

Absolute encoders
 
 

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.

• Channel A and B: The absolute encoders have 2 channels, which are channels A and B. By implementing a second channel B with the phase position displaced by 90°, it is possible to determine the direction of rotation by evaluating the phase-position of the pulses.

• Index: Index contains the reference pulse. This pulse enables the encoder to provide an absolute positional reference increment for each revolution, and makes it possible to recognize an exact angular position following a power failure or after the equipment has been switched off.

• Output Signals: The optical receiver always delivers quasi-sine wave signals. With some encoders, these are available direct from the output port. Most of the encoders have an internal pulse formation device, which delivers square format signals to the output, ready for further processing. The output signal level is controlled by the impulse electronics. With standard transistor outputs, the level is dependent upon the supply voltage from the encoder. This output contains an internal pull-up resistor and is suitable for cable lengths up to six meters.

The potentiometers 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.
 
 
 
 

Limit Switches
 
 

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.
 
 

MOTOR CONTROL
 
 

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 are different.
 
 

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° /minute.
 
 

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 card.
 
 

Stepper motors
 
 

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.
 
 

Motor controller and driver
 
 

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 controller:
 
 

STEP+/- and DIRECTION+/-
 
 

• STEP+ triggers on the rising edge
• STEP- triggers on the falling edge

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 out gears.
 
 

Software
 
 

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 card.
 
 
 
 

Control System
 
 

Interface
 
 

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.
 
 

Computer
 
 

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:
 
 

• Soyo Tek SY-6BB AT PII Motherboard with a 100 MHz bus
• Intel Celeron 266 MHz processor
• 64 Mb of SDRAM
• Trident MPEG 4 Mb EDO video card

I/O Card
 
 

• Elevation Position (Analog)
• Azimuth Position (Analog)
• 4 limit switches (Digital)

• Elevation Motor (Analog)
• Azimuth Motor (Analog)

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.
 
 
 
 

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 LabView.
 
 

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

1. m = (360 – 0)/(5 – (-5))
2. b = 180

1. m = (86.5 – 0)/(5 – (-5))
2. b = 86.5/2 = 43.25

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:
 
 

Azimuth

• G = -(5) / (360 – 0)
• G = -0.01389
• MC = 0.01389 * (AP – DP)

• G = -(5) / (86.5 – 0)
• G = -0.0578
• MC = 0.0578 * (AP – DP)

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.
 
 
 
 

RECEIVER
 
 

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 frequency.
 
 

1. The frequency should be such that a stable high-gain amplifier can be economically attained.
2. The frequency has to be low enough so that it can provide a steep attenuation characteristic outside the bandwidth of the IF signal. This decreases the noise and minimizes the interference from adjacent channels.
3. The frequency needs to be high enough so that the receiver image response can be made acceptably small.

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:
 
 
 

Components	Center Frequency (MHz)	Gain (dB)	Noise Figure (dB)	Bandwidth (MHz)
1) Pre-select Filter	1200 – 1700	/	?	1200 - 1700
2) Low Noise Amplifier	1200 – 1700	25	1.3	1200 - 1700
3) Mixers	/	8	17	/
4) 1st IF Filter	200	?	?	200 (adjustable)
5) 1st IF Amplifier	200	33	1.9	200 (adjustable)
6) 2nd IF Filter	40	?	?	10 – 50 (adjustable)
7) 2nd IF Amplifier	40	50	11	10 – 50 (adjustable)
8) Low Pass Filters	0	?	?	10 – 50 (adjustable)

Receiver Calculations
 
 

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 the Receiver:
 
 

(Excluding Cables & Filters). The equations and values are shown in Table 2.
 
 
 

Components	Gain  (dB)	Gain  G = 10+e(dB/10)	Noise Figure, NF (dB)	Noise Temperature,(K) NT = 290(NF – 1)
1) Low Noise Amplifier	25	G1 = 316.23	1.3	87 K
2) Mixers	8	G2 = 6.31	17	4640 K
3) 1st IF Amplifier	33	G3 = 1995.26	1.9	261 K
4) Mixers	8	G4 = 6.31	17	4640 K
5) 2nd IF Amplifier	50	G5 = 100000	11	2900 K
6) Mixers	8	G6 = 6.31	17	4640 K

Noise factor (F_N) 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.

Where:

F_N 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 T_e. 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:

Where:

T_e is the Noise Temperature

F_N is the noise factor

T₀ is 290K
 
 
 
 

Relating noise temperature to noise figure is as follows:

Where:

T_e 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 Cyber
 
 

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.
 
 

ULTRA CYBER System Specifications:
 
 
 
 

Receiver Design
 
 

Along with the purchase, analysis, and installation of the Ultra Cyber system, a student-designed receiver is being built in parallel with the current project.
 
 

PCB board fabrication
 
 

• Standard
• Miniature
• Sub-Miniature
• Micro-Miniature

• Frequency: 1400MHz
• Low noise figure: 1.3dB @ 1420MHz
• 28dB gain @ 1420MHz
• output matched to 50ohms
• IIP3 = 2.2dBm
• Third order inter modulation level = -34.4dBc

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 is:
 
 

Micro-strip bandpass filter
 
 

The characteristic impedance:
 
 

The w/d of the micro-strip filter is greater than 1, then:
 
 

Down converting part
 
 

1. Operating voltage: 12.0 - 15.5 VDC, 13.8 nominal
2. Current drain: 350mA max.
3. Noise figure: >2.2dB
4. Conversion gain: >32dB standard configuration
5. RF frequency range: 1370 - 1470 MHz
6. IF and LO frequency range: RF - LO = IF
7. 3dB band width: >50MHz

The schematic of the LO is shown below:
 
 

The schematic of the receive converter is shown below:
 
 

Antenna
 
 

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.
 
 

Antenna Calculations
 
 

The gain equation of a parabolic antenna:
 
 

Where:

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:
 
 

Wavelength calculations:
 
 

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 m.
 
 

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.
 
 

Miscellaneous

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 was removed.
 
 

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 enclosure.
 
 
 
 

RECOMMENDATIONS FOR FUTURE WORK
 
 
 
 

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 though.
 
 

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.