School Amateur Radio Club Network
School Amateur Radio Club Network
School Amateur Radio Club Network
School Amateur Radio Club Network
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SARCTRAC Mk2 - Satellite Antenna Rotator Controller and TRACker
Introducing SARCTRAC Mk2, our new Satellite Antenna Rotator Controller and TRACker project, a fully integrated satellite tracking system for portable operation. Simply mount it on a tripod, attach a directional antenna and radio transceiver, then use your WiFi enabled mobile device to select your favourite satellites: SARCTRAC points the antenna at the satellite and controls the radio transceiver so you can listen to space beacons, make two-way satellite contacts an using free third-party software: Download earth images and decode satellite telemetry. It's both fun and educational! New for 2020: The Amateur Radio International Space Station (ARISS) team and NASA have installed a permanent radio repeater on board the ISS. So now you can use SARCTRAC to talk to other Amateur Radio enthusiasts via the ISS!
SARCTRAC was developed so that students at our School Amateur Radio Clubs can have fun and learn about Low Earth Orbiting satellites during our lunchtime sessions.

SARCTRAC takes minutes to set up, in the playground, on a mountain summit, down at our local footy oval or even in the backyard. It starts tracking visible satellites from the selected satellite list right away. To listen and talk to satellites we like to use our Yaesu FT-817 radio, but for some satellites you can just use a hand-held, VHF/UHF FM radio, or even a pair, so you can hear your own signal coming from the satellite. Our School Amateur Radio Club students think SARCTRAC is really fascinating to watch - and so do we. They try to imagine where the satellite is, by looking along the antenna boom and ask: "It's up there?"

The inspiration for SARCTRAC was to help little kids have fun in space: Well, at least to play with things in low earth orbit! You might be surprised just how many tiny cube-sats and regular polar-orbiting satellites there are. The first challenge is to know when are where the satellites will be. Then to point a hand-held antenna up at them for about 10 minutes while they pass overhead. You also have to constantly adjust your radio transmitter and receiver frequencies to compensate for something called Doppler shift. It turned out that our young radio enthusiasts found all that quite challenging, which detracted from the fun of getting to know our new friends in space. It was hard for us, too, just getting everything to work at different schools: So we set about to design a fully automated system.

To make friends with a satellite you first have to know when and where it will be; point a small, directional antenna at it and use an Amateur Radio transceiver to listen or talk through it. It is a bit like fishing in the sky and just as challenging. It is really exciting when the kids hear their first satellite and then realise where it is. They always ask. “Can we talk to it?” We say. “Of course, you can.” But the reality is that satellites move so fast that their position and radio frequency is constantly changing. Tracking a satellite by hand, while trying to tune an Amateur Radio transceiver for a typical 10-minute overhead pass, is a real chore for kids. Setting up an automatic tracking system, with a commercial antenna rotator and all the computers, cables and programs needed, is both tricky and expensive. So, we designed SARCTRAC to be quick and easy for the kids to set up, and now, it does all the work for them. SARCTRAC helps kids spend more time listening to signals from space, receiving data or pictures and even communicating with others via satellites. School kids in space? We say "No problems"!
We first introduced our free, Arduino-based, "Mini Satellite-Antenna Rotator" in 2015. It was a great success, with over 850 radio enthusiasts from around the world building one. Unfortunately, sourcing the correct components, compiling and uploading the software and calibrating the sensor was too much for many who attempted building it. Let alone the pitfalls of setting up and using third-party, satellite-tracking software. And, as much as we love helping our readers out, we realised that we were spending more time supporting them than developing new projects for the kids.

We partly solved that problem by designing an integrated system that just works: SARCTRAC Mk1 took us over 15 months to develop and was the second generation of our 3D-Sensor based antenna rotator. It was half the size of the original unit with many new features. SARCTRAC Mk1 was offered as a DIY kit with all the parts and software required. Unfortunately, it only supported one type of radio: The Yaesu FT-817 and was only suitable for the experienced builder. So, we were still confronted with a large support effort.

In 2020, due to the COVID-19 pandemic, we experienced parts shortages, freight delays and months of home isolation. So we spent another 5 months developing SARCTRAC Mk2: A fully assembled, tested and calibrated product with many more new features.
New Features
  • New Raspberry Pi Operating System
  • New Enclosure with low noise analog regulator and external heatsink
  • New Radio Types supported for Doppler frequency correction
  • New Transmitter and Receiver pairs supported as well as Transceivers
  • New Local Radio Horizon displays realistic AOS and LOS times in built-up areas
  • New Minimum Pass Elevation displays only future passes above a minimum elevation
  • New Pass Predictor displays multiple passes of each satellite
  • New Realtime display updates of visible and future passes every 5 seconds
  • New Single-Touch satellite and pass selection controls
  • New More/Less Passes and Home buttons
  • New Anti-Windup algorithm - Unwinds cables to the home position
  • New Anti-Stall algorithm - Detects, alerts and rectifies motor stall conditions
  • New Multi-Threading with Quad-Core parallel processing
  • New Production-Quality Web Server
  • Powered by: CelesTrak: Two-Line Elements since 1985 by Dr. T.S. Kelso
  • Powered by: Skyfield: Elegant Astronomy for Python by Brandon Rhodes
  • Powered by: World Magnetic Model 24/3/2020 by NCEI and geomag by C.Weiss
  • Powered by: Flask: Web Development One Drop At A Time
  • Powered by: Waitress: Production Quality WSGI Server
We are only offering SARCTRAC Mk2 as a fully assembled, tested and calibrated product. For more details please see our Products page.
See some videos of SARCTRAC working on our SARCNET YouTube Channel:

  • Setup
    • Tripod-mounted for portable operation and quick set-up - Easily splits into two separate pieces: Tripod/rotator and antenna/lift-arm.
    • DC powered for battery or solar operation - Typically uses the same power source as the radio.
    • Integrated rotator and controller in one unit - Smaller with less cables. No third-party tracking software to wrestle with.
  • Networking
    • WiFi enabled - Works with home WiFi network or WiFi-enabled mobile device with personal hotspot and broadband Internet connection.
    • Internet enabled - Automatically downloads date, time and satellite orbital elements from the Internet.
    • WiFi enabled mobile device used for control and display - No cables to separate PC or laptop.
    • Built-in web server accessible by any web browser on the WiFi network - No tracking applications to install and configure.
  • Start-up
    • Displays satellite SELECTION, satellite TRACKING and radio TUNING web pages - Logically organised pages.
    • Start-up alert tones - Warn of disconnected USB CAT Cable, GPS or 3D Sensor.
    • Access to START/STOP, RESTART and SHUTDOWN buttons on each web page - Important for rotator safety and tracker control.
    • Starts with motors stopped - Operator action is required to start motors after power up for safety.
    • Displays Local Time with Time Zone selection - Easier for scheduling.
    • Date and time information provided by built-in GPS receiver or Internet time source - No clock setting required.
    • Latitude and Longitude information provided by built-in GPS receiver - No station location entry required.
    • Uses last saved location until GPS is available - Quicker startup.
    • Stops polling GPS when location error is minimised -   Reduces processor load.
    • Displays reverse geocode address lookup - Confirms that the correct latitude and longitude is used.
    • Antenna pointing information provided by boom-mounted 3D Sensor (magnetometer/accelerometer) - No compass calibration or leveling required.
    • Magnetic inclination and declination information provided by built-in World Magnetic Model - No online searching for local magnetic offsets.
    • Satellite orbital element information updated from Internet each day - No manual download required.
    • Satellite position determined from the latest SGP4 orbital predication models - More accurate tracking.
    • Uses last saved satellite selection - Quicker startup.
  • Satellite Selection
    • Access to thousands of satellite orbital elements over the Internet - Distributed by Dr. T.S. Kelso at since 1985.
    • Permits user-entry of selected orbital element library URLs - Select which satellite libraries are of interest.
    • Each orbital element library contains hundreds of satellites in different categories, like weather, cube-sats, amateur and NOAA - Select only the categories you want.
    • Permits loading of user-defined orbital element library files - Load pre-launch or unlisted orbital elements.
    • Permits user entry of satellite names to be rejected - Omit whole series of unwanted satellites from the satellite selection list.
    • Displays satellite statistics: Number of each type loaded, duplicates removed, number rejected and the total available - Helps manage your satellite database.
  • Satellite Tracking
    • Tracks only selected satellites - Schedules tracking of each satellite in turn.
    • Satellites displayed in order of their Acquisition Of Signal (AOS) time - Provides a next pass schedule.
    • Displays next-pass, AOS time, azimuth and max elevation for each selected satellite - Easy to decide which satellite passes to track.
    • Displays currently tracked satellite azimuth, current elevation and LOS time - Easy to compare current satellite LOS time with next satellite AOS time.
    • Automatically points the antenna at a visible satellite - No manual antenna steering required.
    • Built-in alert tone indicates immanent antenna movement - Safer operation. Alerts at the start and end of the current pass.
    • Permits selection of any one of multiple visible satellites - Compare and select the best of the currently visible passes.
    • Automatically re-positions antenna ready for the next pass - No waiting at the start of each pass.
    • Motor stall warning with anti-stall shaker - Prevents motors stalling uner certain conditions.
    • Intelligent anti-windup algorithm - Unwinds the cables in between passes.
    • Tracks multiple selected satellites in turn - No resetting selections between passes.
  • Radio Control
    • Radio CAT control enabled - Automatically controls the radio frequencies and modes.
    • Automatically controls the radio frequencies correcting for satellite Doppler shift - Accurate frequency control.
    • Satellite beacon/transponder frequency and mode information provided by built-in satellite database - No online searching for satellite data.
    • Permits selection of known satellite beacons or transponders - Useful to check the beacon frequency if the transponder is not heard.
    • Permits manual adjustment of transmit and receive frequencies and modes - Useful to avoid interference and use the transponder bandwidth more efficiently.
  • Sensor Calibration
    • 3D Sensor is calibrated at the factory. Recalibration is possible if magnetic conditions change.
    • Provides manual Start, Abort and Save calibration controls with tone feedback - Easier and more accurate calibration.
  • Miscellaneous
    • Reduced Radio Frequency Interference using analog regulators and RF chokes - Easier to hear selected satellites.
    • DC reverse polarity protection - Setup at night with no more smoke and tears.
    • Stall resistant motors and gearboxes with all metal gears - Safer operation with longer lasting gearboxes.
  • Enclosure Size: 145x105x65mm (5.7x4.1x2.2inch)
  • Ingress protection: IP68 sensor. IP65 enclosure.
  • Operating voltage: 12-15VDC (min - max)
  • Operating current: 1A (typical)
  • Regulatory Compliance: Same as for the Raspberry Pi model 3B+
  • Maximum startup time: 60 seconds (max)
  • Antenna rotation speed: 0.6 RPM azimuth and elevation (max)
  • Sensor cable length: 1m
  • Power cable length: 1m
  • USB CAT Control Ports: 2
  • Radio modes supported: AM, FM, CW, USB and LSB
  • Radio baudrates supported: 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200
  • Supported receivers/transmitters: Notionally, any receivers/transmitters supported by HAMLIB's F and M commands
  • Supported transceivers: Notionally, any transceivers supported by HAMLIB's F, M, I, X and S commands.
  • Supported USB CAT cables: Notionally any USB to serial converter with compatible voltages and connectors that use devices supported by Linux including genuine chipsets such as FTDI, CH-340, but not PL2303
  • The following radios have been verified:
    • Yaesu FT-817
  • The following USB CAT cables have been verified:
    •  Yaesu CT-62
Important: We do not claim any particular radio or CAT cable is supported until we have either verified it ourselves or have received credible reports of its interoperability. Until then, comptibility is either experimental or non-existent.
Radio Control
Notwithstanding the above caveat, our research shows that some assurance of radio interoperability may be obtained from the HAMLIB version 3.3 rigctrl program, itself, which reports support for the specific radios shown in the following list:

R = A Receiver, with a serial control port, which supports the HAMLIB F and M commands.
T = A Transmitter, with a serial control port, which supports the HAMLIB F and M commands.
X = A Transceiver, with a serial control port, which supports the HAMLIB F and M commands and in addition supports split mode VFO operation using the HAMLIB I, X and S commands.

  1. A transceiver should be capable of operating as either a receiver or transceiver.
  2. The first USB CAT cable to be connected to SARCTRAC after power up is considered the receiver or transceiver
  3. The second USB CAT cable to be connected SARCTRAC after power up is considered the transmitter or is ignored
  4. If both USB CAT cables are connected to SARCTRAC before power up, their assignment is generally persistent  

Unavoidable known problems:
  1. Some receivers produce an audible "click" when the receiver VFO is updated.
  2. Some transmitters and transceivers do not permit their frequency to be changed while transmitting.
  3. Some transceivers must switch to the transmitter VFO to update it, causing momentary reception of the uplink frequency.

Radio control and the selection of the radio types used is therefore considered an experimental capability.

RadioType RadioModel, RadioCapability
  • AOR AR2700, R
  • AOR AR3000A, R
  • AOR AR3030, R
  • AOR AR5000, R
  • AOR AR5000A, R
  • AOR AR7030, R
  • AOR AR7030, R
  • AOR AR8000, R
  • AOR AR8200, R
  • AOR AR8600, R
  • AOR SR2200, R
  • DRAKE R-8A, R
  • DRAKE R-8B, R
  • ICOM IC-1275, T
  • ICOM IC-271, T
  • ICOM IC-275, T
  • ICOM IC-471, T
  • ICOM IC-475, T
  • ICOM IC-735, T
  • ICOM IC-751, T
  • ICOM IC-761, T
  • ICOM IC-775, T
  • ICOM IC-78, T
  • ICOM IC-820H, T
  • ICOM IC-821H, T
  • ICOM IC-970, T
  • ICOM IC-PCR100, R
  • ICOM IC-PCR1000, R
  • ICOM IC-PCR1500, R
  • ICOM IC-PCR2500, R
  • ICOM IC-R7000, R
  • ICOM IC-R71, R
  • ICOM IC-R7100, R
  • ICOM IC-R72, R
  • ICOM IC-R75, R
  • ICOM IC-R9000, R
  • ICOM IC-R9500, R
  • ICOM ICR-8500, R
  • JRC NRD-525, R
  • JRC NRD-535D, R
  • JRC NRD-545, R
  • KENWOOD R-5000, R
  • KENWOOD TS-140S, T
  • KENWOOD TS-2000, X
  • KENWOOD TS-440, X
  • KENWOOD TS-450S, X
  • KENWOOD TS-480, X
  • KENWOOD TS-570D, X
  • KENWOOD TS-570S, X
  • KENWOOD TS-590S, X
  • KENWOOD TS-680S, T
  • KENWOOD TS-690S, X
  • KENWOOD TS-711, T
  • KENWOOD TS-790, X
  • KENWOOD TS-811, T
  • KENWOOD TS-850, X
  • KENWOOD TS-870S, X
  • KENWOOD TS-930, T
  • KENWOOD TS-940S, X
  • KENWOOD TS-990S, X
  • LOWE HF-235, R
  • RACAL RA3702, R
  • RACAL RA6790/GM, R
  • SKANTI TRP8000, T
  • TAPR DSP-10, T
  • TEN-TEC RX-320, R
  • TEN-TEC RX-331, R
  • TEN-TEC RX-340, R
  • TEN-TEC RX-350, R
  • TEN-TEC TT-516, X
  • TEN-TEC TT-538, X
  • TEN-TEC TT-565, X
  • TEN-TEC TT-585, X
  • TEN-TEC TT-599, X
  • YAESU FRG-100, R
  • YAESU FRG-8800, R
  • YAESU FRG-9600, R
  • YAESU FT-100, X
  • YAESU FT-1000MP, T
  • YAESU FT-1200, X
  • YAESU FT-2000, X
  • YAESU FT-450, X
  • YAESU FT-817, X
  • YAESU FT-840, X
  • YAESU FT-857, X
  • YAESU FT-890, X
  • YAESU FT-897, X
  • YAESU FT-900, X
  • YAESU FT-950, X
  • YAESU FT-980, T
  • YAESU FT-990, X
  • YAESU FT-DX5000, X
  • YAESU FTDX-9000, X
  • YAESU VR-5000, R
Please read the following very carefully. We accept no responsibility or liability for the following:
  • This is partly a DIY project for the experience builder. We are not responsible for your time, costs, tools, availability or substitution of parts.
  • Beware of moving parts - Unit may move at any time without warning. Do not stand or permit anyone to stand in the vicinity of the operating unit.
  • Beware of eye hazard - Moving satellite antennas are prickly. Eye protection is recommended.
  • Beware of pinch hazard - Keep fingers away from moving parts.
  • Beware of electromagnetic radiation hazard - Do not use with high power transmitters. Recommend 10 Watts maximum.
  • Beware of electrocution hazard - Do not use near power lines.
  • Beware of lightning hazard - Do not use in thunderstorms, rainy or windy conditions.
  • Beware of fire hazard - The unit has no built-in over-voltage or over-current protection.
  • Not suitable for unattended operation.
  • Not suitable for fixed or permanent outdoor operation.
  • Automatically connects to the Internet: Adult permission and charges may apply.
  • Constant adult supervision of the operation is required to prevent injury, especially around children.
  • Constant adult supervision of the operation is required to prevent damage to the unit, anything attached to the unit or anything in the vicinity of the unit.
  • Constant adult supervision of the operation of radio transmitters is required at all times. You must check your licence conditions and operating frequency.
  • Antenna, tripod, lift-arm, mountings, cables or anything in the vicinity of the unit may be damaged under normal operation or due to software malfunction.
  • The motors are light-duty: Do not force them or drop or bump the tripod. Avoid striping the metal gears.
  • Installation of a safety DC cut-off switch is recommended.
We have conducted the following safety testing of the completed project:
  1. Motor stall: The motors do overheat or draw excessive current under full-power, stalled conditions.
  2. Cable windup: A restrained power or coaxial cable is not damaged under full-power windup conditions.
  3. Antenna impact: The Arrow™ Antenna elements were not damaged under full-power impact with stationary object or under restraint conditions.
  4. Human impact: The human operator was not damaged under full-power impact with the antenna. Note: Eye damage could occur even when the antenna is motionless.

  • Suitable for rotating only a single, small directional antenna (e.g. A handheld, dual-band, Yagi antenna such as an Arrow™ antenna) using a counterbalanced lift-arm.
  • Currently only suitable for controlling the radios which are controllable using HAMLIB commands F, M, X and S. See specification for a list of verified radios.
  • Unit will oscillate unless solidly mounted only on a rigid stand, such as a heavy-duty (speaker) tripod.
  • Any formatting or data errors in the configuration files will stop the operation of the unit. Always keep a backup of the working configuration files.
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