In January we posted about the AntRunner, which is a $325 (incl. shipping) satellite antenna rotator shipped from China. Recently we've come across another low cost satellite rotator from Australia called the "SARCTRAC Mk3b" which was developed as part of a school amateur radio educational program. This rotator fully assembled comes in at AU$400 + AU$50 worldwide shipping (US$290 + US$40 = US$330), making it's price comparable with the AntRunner. SARCTRAC can be purchased from the sarcnet products page. Currently only the fully built unit is available, but in the future they plan to offer a cheaper kit option.
We're yet to test the SARCTRAC Mk3b, but based on an overall review of it's advertising, it appears that the SARCTRAC has some superior specifications and a superior design when compared to the AntRunner.
Unlike the AntRunner, SARCTRAC comes with all its components enclosed in a waterproof IP65 rated enclosure. Its design also makes use of a 3D position sensor with magnetometer, allowing the unit to know its orientation at all times, meaning that it should be able to automatically position itself from startup. The design also makes use of DC motors with a built in worm gear drive, so the the motors back driving is not possible.
The system is controlled via a built in Raspberry Pi 3B+ and can communicate with the controlling PC via WiFi. Raspberry Pi's have stable WiFi connections, so we shouldn't see the connection problems that we had with the ESP32 based AntRunner.
Just like the AntRunner, SARCTRAC is only a lightweight rotator with torque specs of 50kg.cm static and 25kg.cm dynamic. So it should be able to handle counterbalanced Yagi beams, and lightweight dish antennas.
SARCTRAC Mk3 Satellite Antenna Rotator Controller and TRACker
Weather satellites that transmit HRPT give you high resolution uncompressed images of the earth. With an SDR, L-band feed, 60 cm or larger satellite dish and LNA+filter these images can be received by anyone. Derek OK9SGC has the definitive HRPT reception tutorial available here. However, as these are low earth orbit satellites, the user is required to find a way to track the satellite as it moves across the sky. With some skill and experience, hand tracking can work, but a motorized solution is really what is desired. Other applications such as ham satellite communications as well as radio astronomy projects may also benefit from motorized tracking .
Antenna rotators that rotate in azimuth and elevation can be used to track satellites moving across the sky. The problem is that antenna rotators are typically very expensive, or are a major task to DIY, involving circuit construction and 3D printing of parts.
Recently on Tindie we came across the "AntRunner" which is a relatively low cost portable antenna rotator from China coming in at US$325 with free shipping to most countries (VAT is added for the EU as $50 in shipping fees).
AntRunner is based on two geared stepper motors, a motor controller PCB and an open frame. AntRunners code is open source, as well as some partial hardware schematics.
It can be interfaced via a USB serial connection or through WiFi via it's onboard ESP32 chip, and it relies on the Hamlib 'rotctl' software library running on either the controlling PC, or another intermediary device like a Raspberry Pi. Once setup, software like Gpredict on the PC or Look4Sat on Android devices can be used to control the rotator.
We ordered an AntRunner for testing with our own funds. Our setup involved a USB connection from the AntRunner to a Raspberry Pi, 12V plug pack and a 60cm dish. We installed hamlib on the Raspberry Pi, and used Gpredict (PC) and Look4Sat (Android) on networked devices to send the desired elevation and azimuth commands to hamlib on the Raspberry Pi for particular satellites.
(Note that if you are installing hamlib for the AntRunner, you should do so from source as the packages in Ubuntu 22.04 appear to be out of date. And the older version of hamlib installed via Ubuntu does not support the AntRunner).
Overall the AntRunner works as expected and was easily able to follow HRPT satellites across the sky. It was also great for easily pointing and switching between geostationary satellites like GOES and GK-2A. It easily held and moved a 60cm dish and feed which weighs about 3 kg. The specs of the AntRunner indicate 5 kg max load (although the GitHub specs note 10kg), so it should be able to hold larger diameter dishes as well.
However we did have an issue with the advertised WiFi connection which is an alternative to the USB serial connection. When connected to WiFi the connection would always drop after a single movement command was sent, and it would never reconnect unless rebooted twice. For this reason we abandoned WiFi and only used the USB serial connection, and communicated wirelessly via the Raspberry Pi. There is also a WiFi web interface available for testing movement commands and setting up the WiFi connection, but it is only in Chinese.
It's possible that RF noise from the motors was causing the WiFi disconnection, but on the frequencies that L-band satellites operate at, we did not notice any motor interference.
The AntRunner is advertised as a portable rotator, so that means it is not suitable for use in poor weather as it has no cover to protect the motor circuit board and motors themselves from rain. However, it is certainly small and light enough to be portable. You just need a portable 12V power supply as well.
Another issue is that when power is lost, the motors will spin freely, resulting in the antenna coming crashing down fast. So care must be taken when powering down with someone there to hold the antenna. The user is also required to physically hold the antenna level at 0 degrees elevation before powering up the AntRunner, so that it will reference 0 degrees elevation. Once powered the antenna holds in place.
There are also no limit switches on the device, so if an erroneous command is sent, it could send the motors into a position that could damage something.
Overall if you want something cheap and pretty much ready to use out of the box for tracking HRPT or other LEO satellites, the AntRunner is a good budget choice if you intend to only setup temporary stations. It is not suitable for permanent satellite receiver setups, at least not without some modifications.
A similar product is the SATRAN MK3 which was a 3D printed kit costing 175 Euros + shipping, but unfortunately this product appears to no longer be sold.
The ultimate in low cost rotators is probably the SatNOGS V3 rotator, but as mentioned this is a DIY project that requires a significant time commitment as it involves 3D printing multiple parts, sourcing components, building PCBs and constructing everything together. We have found one company offering a SatNOGs hardware kit, containing all of the parts required for US$445.
Compared to the SATNOGS design, the SATRAN design appears to be much simpler and easier to build. Although being a smaller unit it's only design to handle small compact antennas such as a 70cm Yagi. SATRAN is also controllable via a web interface and there is an Android App. The design is capable of rotating 360 degrees, and 110 degrees from zenith, which allows a user to cover the entire sky.
Daniel notes that SATRAN kits should be available for sale from Feburary/March 2021. He also notes that it is possible to 3D print most of the parts and to just purchase the electronics for a lower price.
OpenAstroTracker is a recently published open hardware 3D printed tracking mount designed to move DSLR cameras for astrophotography. The mount supports heavy long lenses, so we think that this mount could also have the ability to move long directional antennas for satellite tracking. It could also be interesting to modify it for automatic aircraft photography, similar to what we've seen in this previous post where a Raspberry Pi camera on a pan-tilt mount was used with ADS-B data from an RTL-SDR to track aircraft in the sky with the camera.
The 3D printer files are available on Thingiverse, and the mechanical and electronics build guide, and Arduino code is available on GitHub. The build seems to be quite a bit easier compared to a SatNOGS rotator which is another 3D printed open hardware rotator, but it is yet to be seen what sort of antenna sizes it could rotate.
An antenna rotator can be used to automatically point a high gain directional antenna such as a Yagi at a low earth orbit satellite which passes overhead relatively quickly. Such as antenna can be easily connected to an SDR like the RTL-SDR to receive data such as HRPT weather satellite images from satellites.
Manuel's antenna tracker is inspired by the SatNOGs rotator, but he writes that his one was designed to slightly to be smaller and more powerful. For the driving motors he uses NEMA23 steppers which are mounted in a frame made out of 2020 aluminum extrusions. An Arduino Nano with optical end stops controls two TB6600 stepper drivers which control the motors. The rest of the parts such as brackets and gears are all 3D printed.
Attached to the antenna rotator is Manuel's home made carbon Yagi antenna. He also attempted to use his 1.2m dish but found that the rotator could not handle the weight.