Satellite Tracker for Leo Satellites

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SCLP TRACKER

A SIMPLE LOW COST PORTABLE SATELLITE TRACKER

FOR LOW EARTH ORBIT SATELLITES

MIKE STIPICK – KC4RI

Although the United States and Russia are still the largest players in

Space, more countries such as France, India, Japan and China,

along with free enterprise companies such as Space X and Orbital

Sciences have developed satellite launch capability. With the advent

of the cube-sat and micro-sat, more satellites are finding their way

into space. Unlike commercial satellites that are often in



geostationary orbit, these new satellites are in Low Earth Orbits thus

they are called LEO’s for short. Most Leo’s are in an orbit of between

300 and 500 miles high. Therefore it does not take a large antenna

array or high power to communicate using these satellites. Some of

these satellites like A0-51 can be worked with a 5 watt 144/432 MHz

handheld FM radio.

Because of the low orbit, the time window to work them from one

horizon to another is fairly short, usually between 10 to 15 minutes

maximum. Also the direction that they rise and set usually varies

considerably from orbit to orbit. Therefore good tracking software

such as SATPC32 or NOVA is very useful. There are three ways that

hams cur rently use to track the LEO’s:

(1) hand pointing and waving

(2) tripod assisted pointing

(3) automatic tracking systems

The first two techniques are economical and quite portable. With a

little practice one can become fairly proficient at finding and

working most satellites. However it is often difficult to handle the

antenna and work the radio at the same time. The automatic

tracking system allows one to easily and more accurately track the

satellites so the operator can concentrate on the QSO and operating

the radio. Most automatic tracking systems are not very portable.

The idea behind the SLCP was to provide the accuracy of the

automatic systems and provide the portability of the tripod and

handheld systems.

The two most popular antennas for operating the LEO’S are the Arrow Model 146/437 -10WBP and the ELK 2M/440L5. Figure 1 shows

the Arrow Antenna. It is a hand held crossed Yagi design with 3

elements for 144 MHz and 7 elements for 432MHz. Each antenna can

be separately fed or Arrow offers a low power diplexer that will fit in

the handle of the antenna.



Figure 1

Figure 2



Figure 2 is the ELK 2M/440L5. It is a hand held log periodic antenna

that covers from 144 MHz through 432 MHz and does not require a

diplexer. It can be fed with a single feed line.

Figure 3

Figure 3 is a tripod assisted pointing design that also holds two

separate handheld radios for the uplink and downlink. The radios

help balance the system by providing a counter balance to theantenna. This system is light weight, portable and easy to assemble

and disassemble.



Figure 4

Figure 4 is a roof mounted automatic tracking system using a Yaesu

G5500 rotor and multi element Yagi antennas. The advantage of this

type of system is that it is quite robust and supports large antenna

arrays which will allow one to hear the satellites closer to the

horizon. There are a variety of computer interfaces for the Yaesu AZ/EL rotors and this allows precision tracking. This type of system

is quite expensive and is not very portable.



Figure 5 is a Computer Interface available from AMSAT developed by

Howard Long – G6LVB

Figure 6 - SATPC32 Tracking software



DESIGN OBJECTIVES

• LOW COST - $300 - 400 ( LESS THAN HALF THE PRICE OF

CURRENT SOLUTIONS)

• LIGHT WEIGHT & PORTABLE

LESS THAN 10 LBS AND MOUNTS ON A CAMERA TRIPOD

CAN BE EASILY LIFTED WITH ONE HAND

CAN BE OPERATED FROM AC POWER OR A 12 VOLT SUPPLY

• EASY TO SET UP

LESS THAN 5 MINUTES NOT COUNTING THE ANTENNA

SELF CALIBRATING – AZ & EL

• COMPUTER CONTROLLED

USB INTERFACE WITH EASYCOM PROTOCOL - COMPATIBLE

WITH CURRENT TRACKING SOFTWARE

• FIRMWARE UPGRADEABLE

• SIMPLE DESIGN THAT IS EASY TO MANUFACTURE

• AVAILABLE AS A KIT OR ASSEMBLED

• KIT IS EASY TO ASSEMBLE - FEW OR

NO SURFACE MOUNT PARTS

AVAILABLE FOR ARRISSat- 1



SYSTEM OVERVIEW

LAPTOP

COMPUTER

AND

SATELLITE

TRACKING

SOFTWARE

STEPPER

MOTORS

AND

MECHANICAL

ASSEMBLY

COMPASS

CHIP

POWER

SUPPLY

PIC MICRO

CONTROLLER

BOARD

USB

I2C



PROTOTYPE MICRCONTROLLER

MICROCONTROLLER

PIC 18F4320

LCD DISPLAY

USB CHIP

FT232R

ELEVATION

STEPPER MOTOR

CONTROLLER

FIRMWARE

UPDATE PORT

USB CONNECTOR

POWER SUPPLY

+12 +5

AZIMUTH

STEPPER MOTOR

CONTROLLER

TO CONNECTOR BOARD

INPUT POWER

CONNECTOR

12-14 VOLTS



MICRO CONTROLLER SCHEMATIC



STEPPER MOTOR CONTROL

SCHEMATIC



CONNECTOR BOARD

SCHEMATIC



POWER SUPPLY

SCHEMATIC



STEPPER MOTORS – NEMA 17

A3967 STEPPER MOTOR

CONTROLLER ASSEMBLY

Stepper motors and a smart stepper motor controller were used to

provide azimuth and elevation controll. These motors provide hightorque and acurrate positioning, while using a realitively modest

amount of current at 12 volts. They also hold their position when

stopped. The A3967 contoller is easily intefaced to the Pic

Microcontroller. Micro stepping is available with the A3967 but has

not been implemented in the prototype phase. The chip was

purchased as a complete assembly on a small board so one does not

have to solder a surface mount device. By using a socket it is easily

replaced in case of failure.



USB CHIP

The USB Chip used to connect between the host computer running the

satellite tracking software and the Pic Microcontroller is the FTDI

FT232R. This chip converts USB messages to RS-232 Serial Format.

This allows one to easily interface to the USART on the PIC

Microcontroller. Only the receive functions are currently

implemented in this design. This chip can be mounted on a small PC

board so that it can be socketed thus eliminating the need to solder

surface mount componets.



COMPASS CHIP

A compass chip is used so that the system azimuth is self calibrating.

Just set it down. It always knows where it is pointed relative to

Magnetic North. No alignment or calibration is needed. Like any

compass it can be affected by large magnetic fields. The initial design

placed the elevation stepper motor too close to the compass chip. This

caused errors in the compass readings. Currently no attempt hasbeen made to compensate between True an Magnetic North. This chip

is provided on printed circuit board so no surface mount soldering is

required.



MECHANICAL DETAILS

ELK OR ARROW

ANTENNA

ELEVATION

BELT DRIVE

CONNECTOR

BOARD

COMPASS CHIP

COUNTER

BALANCE



MECHANICAL DETAILS

AZIMUTH

STEPPER

MOTOR

SWIVEL

BEARING

ELEVATION STEPPER

MOTOR MOUNTED

INSIDE FIBERGLASS

SUPPORT

NON METALLIC

FIBERGLASS

SUPPORT



Development Environment

• SOFTWARE

MICRO CHIP MPLAB IDE VERSION 8.53

MICRO CHIP C18 C COMPILER

QL – 200 EVALUATION PLATFORM WITH QL – PROG

EXPRESS PCB SCHEMATIC AND BOARD LAYOUT

• HARDWARE

HP 1661CS LOGIC ANALYZER

HP 54600A DIGITAL OSCILLOSCOPE

HP DIGITAL VOLTMETER

HP 35S AND 16C POCKET CALCULATORS

The software for the Pic Microcontroller was developed using the

Micro Chip C18 Compiler. This was much easier to use and document

than writing in assembly code. Much of the software was initally

tested on a QL-200 Evaluation Board and the QL-200 on board

programmer was used to program the Pic Microcontroller.

This a real time system when tracking a satellite and it is

performing numerous calculations and IO at once:

Read and parse the USB messages from the USART

Commincate with the compass chip via the I2C bus

Calculate the tracking values and commuincate with the both

the azimuth and the elevation stepper motor controllers.



Output messages to the LCD Display

Read the front panel switches

In a project of this complexity it is important to have the proper test

equipment to verify proper operation and debug problems. Without a

good logic analyzer and a good oscilloscope this project would

probably not have been successful. Test points for all of the IO were

designed into the initial prototype boards. If you cannot probe a

point, then you can’t measure it! Measuring the timing between

various signals was often critical as well as monitoring the data flow

on the serial busses. Figure 7 shows the test equipment used.

W HAT’S NEXT ?

I am currently making a few small modifications and enhancements

to the design. This includes new printed circuit boards and some

slight modifications to the mechanical design. I hope to show my

improved final design at the SVHFS Conference at the end of April

2011. Information will be posted on my website www.kc4ri.com . If

there is enough interest I will try to put together some kits for those

that want to build and experiment with an SCLP prior to the launch

of ARRISSat 1 in July.

http://www.kc4ri.com/






DEVELOPMENT EQUIPMENT

Figure 7

HP VOLTMETER

HP 35S CALCULATOR

QL -200 DEVELOPMENT

BOARD

HP 54600

OSCILLOSCOPE

HP 1661CS

LOGIC

Documents

Satellite Tracker for Leo Satellites