Category: Antennas

Build a Cubesat Reviews a Discovery Drive Prototype and Sets up SatNOGS

Over on YouTube Manuel from the 'Build a Cubesat' channel has uploaded a video testing a prototype version of our Discovery Drive antenna rotator. If you are unaware, Discovery Drive is our new antenna rotator product for applications like satellite tracking and general antenna positioning that is currently being crowd-funded over on Crowd Supply. There are two days left in the campaign.

In the video, Manuel overviews the Discovery Drive, shows the internals, and walks us through the web UI. He goes on to show how it can be set up with the SatNOGS project. The SatNOGS project has volunteers set up ground-based satellite stations, and anyone can use those stations to log an observation anywhere in the world.

We note that he mentioned some trouble with getting SatNOGS to rotate the Discovery Drive over zenith. We have added a note to our Wiki showing how this can be fixed by specifying the correct rotational limits for the Discovery Drive.

Discovery Drive Antenna Rotator Preview

Saveitforparts: Receiving Artemis 2 Signals

Over on the saveitforparts YouTube channel, Gabe has recently posted two videos where he attempts to receive the Artemis 2 signal. His setup consists of a surplus satellite dish inside a geodesic radar dome at his "Sandland" radio observatory, a 3D-printed feed, a HackRF One SDR, and various LNAs, including a dedicated S-band unit from LMA Scientific. He used GPredict for tracking and SDR++ for spectrum analysis, targeting the expected downlink frequency around 2216.5 MHz.

The main challenges were the capsule's low elevation angle from his location in Minnesota, rapidly changing orbital elements that made TLE-based tracking unreliable during the trans-lunar injection burn, and the fact that all telemetry is encrypted. During his first overnight session, he was only able to detect what appeared to be an extremely faint carrier at approximately 2216.49 MHz, which is consistent with the expected Doppler-shifted frequency, which disappeared when the dish was moved off-target. In a second session timed to catch a handover between NASA's Goldstone and Canberra Deep Space Network stations, he received a noticeably stronger carrier signal and even observed sideband activity, though still not strong enough to resolve any modulation detail.

He notes that NASA's original citizen science RFP called for ~9 meter dishes, far larger than his ~2.5 meter setup, and that the capsule also uses a laser communications system for high-bandwidth data. The Canadian Space Dashboard and DSN Now websites proved useful for predicting optimal observation windows during ground station handovers.

Can I Overhear The Artemis II Moon Mission With SDR?

Listening To Artemis II's Return To Earth With DIY Satellite Station

Receiving the Artemis 2 S-Band Carrier With a Wi-Fi Dish and Airspy R2

Thank you to Simone Spadino for writing in and sharing how he received the S-band carrier signal from the Artemis 2 Orion capsule from his home in Italy, using a simple one-meter Wi-Fi grid dish, an Airspy R2, an LNA, a filter, and a downconverter. Simone notes that his results show it is possible to receive the Artemis carrier signal with a small dish.

Artemis 2 may have already returned to Earth safely, but there are future missions planned for 2027 and beyond, so Simone's write-up serves as a great place to get yourself ready to receive those future missions.

Simone's write-up notes that perfect tracking with a rotator wasn't required because the Wi-Fi dish had a beamwidth of about 11°, so he was able to manually orient the dish every 10 minutes using an Android smartphone. On the first night, he achieved a carrier SNR of 5.5dB, and on the second night, 6.5 dB.

Artemis S-Band Carrier Received with Wi-Fi Grid Dish
Artemis S-Band Carrier Received with Wi-Fi Grid Dish

BrowSDR: Turn Your HackRF or RTL-SDR Into a Browser-Based Remote WebSDR

Joel (jLynx), known for his work on the HackRF Mayhem firmware, has released an open-source project called BrowSDR that turns a HackRF or RTL-SDR into a fully browser-based SDR receiver. The application connects to your SDR directly via WebUSB and uses a high-performance Rust/WebAssembly DSP pipeline running in Web Workers for smooth, real-time spectrum and waterfall display. It supports WFM, NFM, AM, SSB, CW, and raw IQ demodulation, along with RDS decoding and POCSAG pager decoding. A standout feature is the ability to open unlimited simultaneous VFOs, each with independent demodulation and DSP settings, with the developer having tested up to 62 running at once.

The real killer feature is remote access. Using WebRTC, you can share your locally connected SDR and access it from anywhere in the world through a browser with no server setup required. BrowSDR also includes built-in Whisper AI transcription that can live-transcribe audio from each VFO independently. The project currently supports HackRF, HackRF Pro, and the RTL-SDR Blog V4, with AirSpy and LimeSDR support coming soon. It also works on Android devices with a USB-C cable. BrowSDR is open source under the AGPL-3.0 license and a live demo is available at browsdr.jlynx.net.

BrowSDR Interface with POCSAG Decoding
BrowSDR Interface with POCSAG Decoding

Measuring Antenna Gain Patterns with Discovery Drive

Our Discovery Drive campaign is currently being crowd-funded on Crowd Supply. Please consider ordering a unit if you are interested in a high-quality, low-power, and portable antenna rotator. Below is an update from the campaign exploring a potential use-case for measuring antenna gain patterns:

In this update, we’ll examine an alternative use case: measuring antenna gain radiation patterns.

One interesting use of a capable Az/El rotator is to measure the radiation pattern of various antennas. This is normally done in an anechoic chamber, but if you have a large enough open space, it can be done cheaply with a rotator and signal source.

To test this as a proof of concept, we used Claude code to very quickly create a tool that could help us create an antenna pattern plot. The software tool simply rotates the antenna on the Discovery Drive one step at a time, measures the SNR using an RTL-SDR, and plots the reading on a graph. To be clear, this simple setup is not providing any sort of calibrated readings, but it will at least give you an idea of what the radiation pattern and performance of an antenna looks like.

In our test, we mounted a TV Yagi on the Discovery Drive and used our software to plot the radiation pattern at 433 MHz. As expected from a Yagi, we see higher gain at the front and lower gain at the rear.

Antenna Gain Results
Antenna Gain Results

Due to a lack of a suitable open area, this test was performed in a small backyard and, hence, the radiation pattern is a little lopsided due to multipath. In this test, we also used a simple omnidirectional antenna for the signal source, which exacerbated the multipath. A way to improve this test would be to use a directional antenna on the transmit side, too.

We will release this open-source tool for others to play with, but please be aware that it was only created for proof of concept. However, if there is interest, we can continue to refine it.

Below is a photo of the physical setup. A HackRF with Portapack and whip antenna are mounted on a tripod a few meters away, while the Discovery Drive carries a Yagi antenna. As the Discovery Drive rotates the Yagi through 0 to 360° in azimuth and -30 to 90° in elevation, it measures the received power at each step.

Antenna Gain Measurement Backyard Setup
Antenna Gain Measurement Backyard Setup

Discovery Drive Campaign Now Live!

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

NanoFarfield: A Portable Far-Field Antenna Measurement Platform (Coming Soon to Crowdfunding)

Thank you to Antenom Antenna Technologies for submitting news about the upcoming crowdfunding campaign for their "NanoFarfield" antenna far field measurement system.

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 Far-Field Measurement System (50–6000 MHz)

Discovery Dish 1420 MHz Hydrogen Line Feed Tested with a WiFi Grid Dish

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
Discovery Dish 1420 MHz Hydrogen Line Feed Tested on a WiFi Grid Dish