We're extremely pleased to announce that our campaign for our Discovery Drive automatic antenna rotator is now live on Crowd Supply! Pricing is reduced during the campaign period, so check it out soon!
Discovery Drive is an automatic antenna rotator designed for use with our Discovery Dish product, as well as similarly sized antennas such as Wi-Fi grid and Yagi antennas.
A motorized rotator, such as Discovery Drive, enables precise tracking of fast-moving polar orbiting satellites using a satellite dish or directional antenna. Examples of polar orbiting weather satellites include METEOR-M2, METOP, and FENGYUN. Depending on your location, you may also have access to other interesting satellites that dump data over specific regions.
In addition to public weather data, operators and enthusiasts might be interested in using Discovery Drive to track CubeSats, and amateur radio operators may wish to track amateur radio satellites.
Amateur radio astronomy hobbyists can map the galaxy in the hydrogen line spectrum using Stellarium, or custom software to aim a Discovery Dish with H-Line feed, allowing you to scan multiple parts of the sky in one night.
Discovery Drive - A Motorized Antenna Rotator Engineered for Discovery Dish
When building and measuring antennas, most people stop at measuring VSWR. However, VSWR is only a small part of the picture for antenna performance. The antenna's far-field pattern determines its gain in a particular direction. Measuring this is typically difficult as it requires a signal source, hiring and travelling to an expensive anechoic chamber, and some sort of automated system to rotate the antenna 360 degrees.
In recent posts, we've seen low-cost DIY solutions explored that use a NanoVNA or RTL-SDR to measure an antenna in an open field (to avoid multipath reflections like an anechoic chamber would) at various points, and then charting the results. However, this is a slow, manual process and requires purchasing and setting up various individual components.
NanoFarfield productizes the low-cost approach, providing a portable measurement system that can be brought into an open environment. The measurement process is automated, by using a motorized rotator which spins the antenna under test 360 degrees in front of a directional signal source. The team write:
As many SDR users know, building antennas is relatively easy, but measuring the actual radiation pattern is often difficult. Normally this requires an anechoic chamber or a large outdoor antenna range, which is usually inaccessible to hobbyists, students, and small labs.
We have been working on a portable antenna measurement system called NanoFarField, designed to measure antenna radiation patterns outside the lab using commonly available VNAs such as NanoVNA or LiteVNA.
Instead of requiring a full antenna range facility, the system allows users to perform radiation pattern measurements in open environments using a compact rotating platform and VNA-based S21 measurements. The goal is to make antenna pattern measurement accessible to:
• SDR and ham radio experimenters • antenna designers and RF engineers • universities and student labs • field testing scenarios
The system effectively acts as a portable antenna range that can fit into a backpack.
Typical workflow:
The antenna under test is placed on the rotating platform.
A reference antenna is positioned at a fixed distance.
The NanoVNA / LiteVNA performs S21 measurements while the antenna rotates.
Software reconstructs the radiation pattern from the measurement data.
This allows users to measure:
• azimuth radiation patterns • antenna directivity trends • relative gain patterns • beamwidth and nulls
without requiring an expensive measurement facility.
Because many SDR enthusiasts design and build their own antennas, we thought this tool could be useful for the community as a low-cost method to visualize antenna performance.
The frequency range is specified at 50 - 6000 MHz, with a typical angular resolution of 1 degrees, and it includes a wideband amplifier to improve results. The hardware is provided as open source, however, the software will be closed source, and provided as a Windows executable.
NanoFarfield: Low-Cost Antenna Radiation Pattern Measurement System (50–6000 MHz)
Thank you to Alex P for writing in and sharing with us his detailed evaluation of the Discovery Dish 1420 MHz hydrogen line feed when paired with a low-cost 1m WiFi grid dish. The goal was to see how well this near off-the-shelf setup performs as a hydrogen line radio telescope. The Discovery Dish feed integrates the dipole very close to the internal LNA and filters to minimize losses, uses a weather-sealed enclosure, and is built around a low-noise Qorvo QPL9547 amplifier, which has a very low noise figure at 1420 MHz.
Alex used 4NEC2 with a simple geometry approximation to analyze the beam pattern and also experimentally determined the optimal feed-to-dish spacing for the WiFi grid. The results show that the Discovery Dish feed significantly outperformed a more standard feed + external LNA setup.
Alex also shows how he uses aluminum foil, or conductive foam, to shield the feed from all signals during a background correction scan. Generally, for background correction scans, we recommend pointing towards a cold area of the sky (any area far away from the Milky Way with little to no hydrogen), but Alex prefers this method.
Discovery Dish 1420 MHz Hydrogen Line Feed Tested on a WiFi Grid Dish
The researchers used a simple off-the-shelf 100cm Ku-band satellite dish and a TBS-5927 DVB-S/S2 USB Tuner Card as the core hardware, noting that the total hardware cost was about $800.
Simple COTS hardware used to snoop on unencrypted satellite communications.
After receiving data from various satellites, they found that a lot of the data being sent was unencrypted, and they were able to obtain sensitive data such as plaintext SMS and voice call contents from T-Mobile cellular backhaul and user internet traffic. The researchers notified T-Mobile about the vulnerability, and to their credit, turned on encryption quickly.
They were similarly able to observe uncrypted data from various other companies and organizations, too, including the US Military, the Mexican Government and Military, Walmart-Mexico, a Mexican financial institution, a Mexican bank, a Mexican electricity utility, other utilities, maritime vessels, and offshore oil and gas platforms. They were also able to snoop on users' in-flight WiFi data.
Cellular Backhaul We observed unencrypted cellular backhaul data sent from the core network of multiple telecom providers and destined for specific cell towers in remote areas. This traffic included unencrypted calls, SMS, end user Internet traffic, hardware IDs (e.g. IMSI), and cellular communication encryption keys.
Military and Government We observed unencrypted VoIP and internet traffic and encrypted internal communications from ships, unencrypted traffic for military systems with detailed tracking data for coastal vessel surveillance, and operations of a police force.
In‑flight Wi‑Fi We observed unprotected passenger Internet traffic destined for in-flight Wi-Fi users on airplanes. Visible traffic included passenger web browsing (DNS lookups and HTTPS traffic), encrypted pilot flight‑information systems, and in‑flight entertainment.
VoIP Multiple VoIP providers were using unencrypted satellite backhaul, exposing unencrypted call audio and metadata from end users.
Internal Commercial Networks Retail, financial, and banking companies all used unencrypted satellite communications for their internal networks. We observed unencrypted login credentials, corporate emails, inventory records, and ATM networking information.
Critical Infrastructure Power utility companies and oil and gas pipelines used GEO satellite links to support remotely operated SCADA infrastructure and power grid repair tickets.
The technical paper goes in depth into how they set up their hardware, what services and organizations they were able to eavesdrop on, and how they decoded the signals. The team notes that they have notified affected parties, and most have now implemented encryption. However, it seems that several services are still broadcasting in the clear.
Thank you to Kaustav Bhattacharjee for writing in and submitting to us his project, where he created a small 11.2 GHz motorized radio telescope with a TV dish and an RTL-SDR. A full description of Kaustav's work can be found in a white paper he wrote on behalf of the Department of Physics at the Indian Institute of Technology Roorkee. In summary he writes:
Briefly put, the hardware Setup comprises a 66 cm parabolic dish, a standard Ku-band LNB with bias tee power injection as the frontend, an RTL-SDR V3 tuned to 1.45 GHz (due to downconversion) as the receiver and a Raspberry Pi 5 handling SDR data (via GNU radio) and stepper motor control (using GPIO pins). A heatmap of the southern sky at 0.9° resolution, showing a belt of geostationary satellites, is the primary result of interest!
We also want to point out that his rotor setup involves several 3D printed gears driven by two NEMA17 stepper motors. However, Kaustav notes that the long term resolution is limited due to cumulative backlash errors from the open-loop control scheme.
Kaustav's 11.2 GHz RTL-SDR Radio TelescopeGeostationary satellites visualized with the radio telescope
VLF (Very Low Frequency) refers to signals in the 3–30 kHz range. Software-defined radios like the SDRplay RSPdx can pick up these signals with an appropriate antenna.
Over on YouTube, @electronics.unmessed has uploaded a video showing how you can build a high-performing VLF loop using a single loop of wire and a balun. The one-turn design results in a naturally low impedance at low frequencies. A balun is then added to step up the impedance, resulting in impedance compatibility with an SDR.
The video explains the concepts behind VLF loops using an equivalent circuit model and shows how conductor thickness offers little benefit above 10 kHz (though wide sheet conductors can add ~3 dB), larger loops scale with area but 2 m is a good indoor compromise, extra turns help small loops but underperform a single turn with a proper transformer, and alternative ferrite mixes give little improvement over standard choke cores. Ultimately, it is concluded that a one-turn loop with a well-chosen balun is one of the most effective designs.
If you're interested in similar content, there are also several other interesting videos on the @electronics.unmessed channel about VLF antennas, mag loop antennas, SDR reception, and more.
Thank you to Nagy István for sharing with us his setup for decoding ADS-C with a 180cm prime focus dish, a cheap Aliexpress LNB, an Aliexpress bias tee, and an SDRplay RSP1B.
István receives the ADS-C signal from the Inmarsat 4A-F4 satellite, which he can see from his home in Hungary.
István also notes the following information about the Chinese LNB:
This LNB original for DVB reception, but it works on Inmarsat reception, 3.6Ghz where ADS-C signals are, without any modification... But sometimes you need correcting frequency because of LNB oscillator drifting. I don't use dielectric plate, I don't have any material for this, at the moment.
Compared to ADS-B, which continuously broadcasts an aircraft’s GPS position and velocity to any ground station or nearby aircraft, ADS-C instead sends position reports via satellite, and is especially used over oceans and remote areas without ADS-B ground receivers.
However, ADS-C is relatively complex for hobbyists to receive due to the need for a large satellite dish and LNB to convert the 3.6 GHz frequency down to a frequency receivable by most SDRs. However, fortunately, as István shows, the LNB can be obtained cheaply these days.
Inmarsat ADS-C decoding with Jaero and Virtual Radar
ADS-C Being Received with an 1.8m dish, cheap Aliexpress LNB and SDRplay RSP1B.
The Wow! signal is a famous, strong, and unexplained radio signal detected in 1977 by the Big Ear radio telescope in Ohio, lasting 72 seconds and appearing to originate from the constellation Sagittarius. Its origin remains unknown, with some speculating that it could be an extraterrestrial technosignature. Upon reviewing the signal data, Astronomer Jerry R. Ehman discovered the powerful signal burst in the readout and wrote a large "Wow!" next to it, unintentionally coining the name.
A network of small radio telescopes offers several distinct advantages compared to large professional observatories. These systems are low-cost and can operate autonomously around the clock, making them ideal for continuous monitoring of transient events or long-duration signals that professional telescopes cannot commit to observing full-time.
Their geographic distribution enables global sky coverage and coordinated observations across different time zones, which is especially valuable for validating repeating or time-variable signals. Coincidence detection across multiple stations helps reject local radio frequency interference (RFI), increasing confidence in true astrophysical or technosignature transient events.
These networks are also highly scalable, resilient to single-point failures, and capable of rapid response to external alerts. Furthermore, they are cost-effective, engaging, and accessible, ideal for education, citizen science, and expanding participation in radio astronomy.
However, these systems also come with notable limitations when compared to professional telescopes. They have significantly lower sensitivity, limiting their ability to detect faint or distant sources. Their angular resolution is poor due to smaller dish sizes and wide beamwidths, making precise source localization difficult.
Calibration can be inconsistent across stations, and frequency stability or dynamic range may not match the performance of professional-grade equipment. Additionally, without standardized equipment and protocols, data quality and interoperability can vary across the network.
Despite these constraints, when thoughtfully coordinated, such networks can provide valuable complementary observations to professional facilities.
The team note that the Wow! signal was strong enough that it could have been detected by a small home radio telescope. They go on to make the case that we could be missing out on detecting many compelling signals simply because radio telescopes aren't watching every part of the sky simultaneously.
The project will monitor the Hydrogen Line frequency for interesting signals. Currently, the team is using a WiFi grid dish and an external LNA as the radio telescope hardware, but they also aim to evaluate our Discovery Dish with H-Line feed.
