Open-Source Phased Array Antenna "open.space" Brings Moon Bounce Communication Within Reach
The Ultimate Ham Radio Challenge: Bouncing Signals Off the Moon
Earth-Moon-Earth (EME) communication, also known as moon bounce, is a technique that uses the Moon as a passive reflector to establish radio contact. Radio waves travel approximately 384,400 km to the Moon and back, taking about 2.5 seconds for the round trip. Since the Moon is visible from roughly half of Earth's surface at any given time, EME theoretically enables communication with stations anywhere in the world that can see the Moon simultaneously.
However, EME has historically been one of the most challenging forms of amateur radio. The Moon's surface reflects only 7-12% of incident radio waves, and the round-trip path loss through approximately 770,000 km of space results in signal attenuation of 250-310 dB. Traditional EME setups have required massive parabolic dishes or stacked Yagi arrays, high-power transmitters (500W to 1kW or more), extremely sensitive receivers with low-noise preamplifiers, and sophisticated tracking systems to follow the Moon's movement across the sky.
In Japan, the first amateur EME contact was achieved in 1975 by JA6DR. Since then, Japanese radio amateurs have conducted EME experiments using borrowed facilities such as KDDI's 32-meter dish at the Ibaraki Satellite Communication Center and JAXA's 18-meter parabola at the Katsuura Space Communication Station. While digital modes like WSJT have made EME possible with lower power levels (around 50W with good antennas), it remains the "ultimate challenge" in amateur radio.
Introducing the open.space Project
"open.space" is an ambitious open-source hardware and software initiative designed to dramatically lower the barrier to entry for EME communication. The project's stated mission is to provide "all the tools needed to experience the thrill of space communication" through an open-source software-defined phased array antenna.
A phased array antenna consists of multiple small antenna elements arranged in a planar configuration, with electronic control over the phase and amplitude of each element. This enables rapid electronic beam steering without mechanical movement, offering a compact yet high-performance alternative to traditional large dish antennas.
Product Lineup and Specifications
open.space offers three product tiers designed for different use cases, with shipping expected to begin in March 2026.
Quad: Software-Defined Radio Tile
The smallest building block is a 4-antenna SDR (Software-Defined Radio) tile that can function as a standalone SDR or serve as a component for larger phased arrays.
- Frequency: 4.9-6.0 GHz (C-band), full duplex
- Per-antenna bandwidth: 40 MHz; 8+8-bit I/Q
- Tx power: 1 W per antenna
- Rx noise figure: ~1.2 dB
- Polarization: RHCP (Tx), LHCP (Rx)
- MEMS TCXO with ~1.4 ps jitter
- FPGA: Lattice ECP5
- Latency: < 1 ms
- Size: 13 cm
- Price: $49-99 (TBD)
The Quad is drop-in compatible with Raspberry Pi pipelines including GNU Radio, Python/C++, and SoapySDR. Standalone applications include general-purpose 4×4 MIMO SDR, fox hunting, direction of arrival (DOA) detection, Open WiFi routers, and drone HD links.
Mini: Starter Phased Array
A compact entry-level phased array composed of 18 Quad tiles (72 antenna elements).
- Array size: 52 cm
- Array gain: ~34.0 dBi
- EIRP: ~52.6 dBW
- Beam steering range: ~60°
- Power: 12 V DC (~450 W peak)
- Price: $899-$1,499
Suitable for high-gain backhaul links, low-Earth orbit satellite downlink reception, long-range drone telemetry, and hands-on phased array experimentation. Extension boards can be added later for array expansion.
Moon: High-Aperture EME Array
The flagship model designed specifically for Earth-Moon-Earth communication, featuring 60 Quad tiles (240 antenna elements).
- Array size: 100 cm (1 meter)
- Array gain: ~39.3 dBi
- EIRP: ~63.1 dBW (equivalent to ~2 kW effective radiated power)
- Beam steering range: ~60°
- Power: 12 V DC (~1.5 kW peak)
- Price: $2,499-$4,999
Beyond EME, the Moon array supports Milky Way C-band imaging, RF sky surveys, terrestrial RF imaging, and atmospheric/ionospheric sensing experiments. It features a coherent distribution network with GPSDO-ready timing for precise beamforming.
Technical Innovation and Discussion
According to discussions on Hacker News, the creator (mrtnmcc) is an RF/DSP engineer from the University of Illinois at Urbana-Champaign (UIUC). A working demonstration was shown at Pacificon, showcasing an end-to-end transmission chain from GNU Radio to a receiver.
Notable technical innovations include custom MASH ΣΔ (sigma-delta) ADCs built from discrete differential pair transistors costing approximately $0.08 each, achieving clean 50 MHz baseband bandwidth. The DACs also use ΣΔ modulation through FPGA LVDS pins with modulating DSP.
The technical community has debated whether the specifications are sufficient for reliable EME. At 5.76 GHz, free space path loss to the Moon reaches approximately 283 dB. The project team's calculations suggest received power of approximately -150.8 dBm with the full array, while the noise floor at 1.2 dB noise figure and 500 Hz bandwidth is -151.9 dBm, yielding an SNR of about +1.1 dB—described as "easily detectable by ear with CW."
The product page notably includes a disclaimer: "Not intended for radar applications. Core functionality needed for radar not included due to export control restrictions."
Regulatory Considerations
Operating open.space requires appropriate amateur radio licensing. In the United States, a Technician class license or higher is required. The product listing indicates "1 per person" for the Moon array, with "country restrictions apply" noted for all models.
In Japan, the 5.6 GHz amateur band (5650-5850 MHz) overlaps partially with the device's frequency range. Japanese operators would need to verify compliance with Ministry of Internal Affairs and Communications (MIC) regulations regarding effective radiated power. For EME operations exceeding 500W, additional approvals involving extensive documentation and inspections are typically required.
A New Era for Amateur Radio
The emergence of open.space represents a potential paradigm shift in EME accessibility. While the $2,499-$4,999 price range for the Moon array is not inexpensive, it is dramatically more affordable than traditional parabolic dish systems with their associated infrastructure costs. The 1-meter form factor also makes installation feasible in locations where massive antenna structures would be impractical.
Modern features like digital beamforming, electronic Moon tracking, Raspberry Pi integration, and software-defined radio capabilities bring EME into the 21st century. The developer has expressed enthusiasm for achieving "mobile moon bounce"—the possibility of EME communication during portable operations.
Beyond Moon Bounce
While EME is the headline application, open.space hardware offers numerous other possibilities: high-gain terrestrial communications, satellite reception, RF direction finding, atmospheric research, and educational experimentation with advanced antenna concepts. The open-source nature means the community can extend and adapt the platform for applications not yet imagined.
Japan has a proud tradition of EME experimentation, viewing moon bounce as the "ultimate expression" of amateur radio. The romance of using the Moon as a relay station to communicate with fellow enthusiasts around the world embodies the original spirit of ham radio—making connections with strangers across vast distances.
Projects like open.space have the potential to bring this dream to more people worldwide. How is amateur radio and EME enjoyed in your country? Have you participated in any challenging communication experiments or worked with specialized equipment? We'd love to hear about your experiences and perspectives on the future of space communication.
References
Reactions in Japan
The era when EME becomes accessible to regular ham radio operators has finally arrived. Until now, you needed to borrow something like a 32m parabolic dish. At around $2,500-$5,000 for 240 elements, this becomes a realistic option for those serious about EME.
Technically very interesting. The DAC design using ΣΔ modulation through LVDS pins and building MASH ΣΔ ADCs from discrete transistors show clever approaches to cost reduction. Whether it actually works for EME remains to be proven though.
C-band huh... In Japan, the 5.6 GHz band (5650-5850 MHz) is allocated for amateur use, but 4.9-6.0 GHz doesn't quite align. Wonder how MIC approval would work.
A boy's heart and an adult's wallet... exactly right lol. EME is the ultimate romance with zero practicality, so I want to support projects like this. Being open-source is wonderful too.
The non-EME applications are interesting too. Milky Way C-band imaging, RF sky surveys - could be useful for amateur radio astronomy. This aperture size at this price is exceptional.
The developer is enthusiastic about 'mobile moon bounce'? EME from portable operations with a 1m array sounds like a dream. Though securing peak 1.5kW power would be challenging.
Can EME really work with these specs? Free space path loss of 283dB, array gain of 39.3dBi, SNR of +1.1dB... seems pretty marginal? I'll remain skeptical until I see actual test data.
Even with phased array tracking the Moon, if steering is limited to 60 degrees, wouldn't you still need a mount to follow the Moon's east-west movement?
>>8 EME is basically a crazy feat where 'achieving contact even for a moment' is the goal, so I don't think constant tracking is necessarily required.
At $49-99 for just the Quad tile, I'd like to try it. Could be fun as a 4x4 MIMO SDR for things like WiFi visualization or DOA experiments. Nice that it connects to Raspberry Pi.
This reminds me of the EME experiments at Hiraiso. Back then we succeeded with 35W using a borrowed 10m parabola. If this project succeeds, it could be useful for science education for young people.
If you can do EME for $5,000, that's kind of cheap in a way, but honestly for people not interested in EME itself, it's just an expensive toy. Satellite communication is more practical.
If it's open-source, will schematics and PCB designs be released? Would be great if we could build it ourselves, but phased array calibration seems difficult for amateurs.
To operate EME in Japan you need a 1st class license, and over 500W requires ministry-level approval with complicated procedures. This antenna's EIRP of 63dBW is equivalent to 2kW, so I wonder if it can clear regulations.
Bouncing radio waves off the Moon and hearing them come back sounds so exciting! Can you at least receive with just a 4th class license?
Expected to ship March 2026. Wonder if they'll ship to Japan. With technical certification issues, importing personally seems like a high hurdle.
EME is finally becoming accessible to regular folks! I've been dreaming of moon bounce for over 20 years but never had space for a big dish antenna. A 1m array might actually fit on my rooftop.
From Germany. Pricing is interesting but I'm concerned about frequency regulations in the EU. C-band allocation for amateur use is limited here. Need to verify if this can be legally operated.
Saw this demo at Pacificon with the UIUC developer. Watching the GNU Radio transmission chain actually work was impressive. He's a really talented RF engineer.
From Brazil. The EME enthusiast community in South America is still small, but if projects like this succeed, more people could try it. Looking forward to it.
I'm skeptical. Read the Hacker News discussion but doubt if CW is really audible at SNR +1.1dB. Won't believe it until I see actual EME QSO video.
From Australia. For EME operators in the southern hemisphere, communication with Europe and North America is limited due to Moon positioning. Hope this compact array changes things.
The note about radar functionality being restricted due to export controls is concerning. The line between what's radar and what's amateur communication is ambiguous.
From France. Electronic beam steering with phased array is a great idea, but ±60 degrees isn't enough for full Moon tracking. You'd still need to manually reorient it on a tripod.
From the US Midwest. People are doing EME with $100 solar cooker dishes, so this project's price point is quite competitive. Being open-source is a big plus.
Japanese living in the US. I once tried to start EME in Japan but gave up because the licensing procedures were too complicated. The hurdles might be lower overseas.
From Netherlands. More interested in other applications of this hardware than EME. Satellite downlink reception, RF direction finding, etc. The $50 SDR tile alone seems worth buying.
I'm an old-timer who's been doing EME for over 30 years. Lowering the barrier to entry is important for passing this wonderful hobby to younger generations. I support this project.
From Russia. We have several EME enthusiasts with huge antenna farms, but this compact array could be revolutionary for urban operators.
From UK. The concept of 'mobile moon bounce' is fascinating. Would be amazing to do moon bounce at Field Day. Power would be the issue though...
From China. Phased array technology is widely used in military and commercial fields, but providing it open-source for amateurs is rare. Wonderful democratization of technology.
From Spain. My husband is a huge EME fan and got excited seeing this project news. Might become a birthday present (expensive though!).