Tx power: 1 W per antenna
Yeah... so free space path loss at legal frequencies for hams this thing can transmit on is ~283dB. Neat idea but consider me skeptical. Having said that I can see some interesting applications for this kind of gear, EME seems overly optimistic though.
A few years ago I was experimenting with 900 MHz LoRa for a work project -- we had need to communicate a very small data payload from inside elevator cabs, with forgiving latency requirements. So we took a LoRa board to a hotel building 2 city blocks away from our lab and cranked the coding gain up to the max, which gave us about a 1 byte payload every second. Perfectly sufficient for our application. Astoundingly, we had great copy in our lab even when the doors of the elevator cab were closed, inside a building 2 blocks away. I can't remember the power level, 500mW I think, but I may be wrong.
63.1 dbW = 93.1 dBm (240 watts + 39.3 dB gain)
path loss at 5760 MHz = 283.2 dB (at perigee)
RX gain = 39.3 dB
93.1 - 283.2 + 39.3 = -150.8 dBm
Noise floor at 1.2 dB noise figure and 500 Hz bandwidth = -151.9 dBm
SNR = +1.1 dB (easily detectable by ear with CW).
Announced on the EME Facebook Group: https://www.facebook.com/share/p/19zLsGZiE7/?mibextid=wwXIfr
Output power was 500w
Was covered on zr: https://www.zeroretries.org/p/zero-retries-0224?#%C2%A7opens... Looks beautiful on a tripod.
The demo was able to show and end to end tx chain from gnuradio to a receiver. Really excited to see this! As there are a myriad of other things that this hardware can be used for as well.
We’re starting with the “Quad” tile — a 4 Tx × 4 Rx SDR designed for arraying — and expect to ship the first units toward the end of this year. They're actually quite capable as a standalone SDR. A Quad can interface directly with a Raspberry Pi 5, and we’ve built a combined enclosure for the SDR + Pi setup. You can run SDR software locally on the Pi or stream IQ samples over gigabit Ethernet to a remote PC.
Software support includes GNU Radio, Pothos SDR, and just about any tool compatible with SoapySDR. We’re also doing some fun demos, like visualizing Wi-Fi signal sources in real time ("Wi-Fi camera") and performing mm-scale 3D localization—a prerequisite for the automatic array calibration.
Larger arrays are assembled by simply tiling these Quads into an aluminum/PCB lattice framework, enabling anything from compact 4-antenna MIMO nodes up to 240-element lunar-bounce arrays. The goal is to have full phased-array capability by March 2026.
The broader vision behind open.space is to make advanced RF and space-communications hardware open and accessible—so anyone can experiment with technologies once limited to national labs: moon-bounce (EME) links, satellite reception, terrestrial RF imaging.
Happy to answer questions here.
One thing I'm excited about getting working is mobile moon bounce!
I assume the goal is to do something cooler than that.
Yes. Bounce the signal off the moon. The moon.
I discussed these possibilities and some more challenging ones in 02013 in https://dercuano.github.io/notes/ultraslow-radio.html, although I was considering laser moonbounce rather than phased-array microwave moonbounce because of the higher antenna gain available.
Caveat: Retroreflectors only reflect in the same direction as the incoming beam. But I'd guess that imperfections in their construction together with the roughly 1 degree of arc spanned by 2 stations on opposite sides of the earth might make this idea practical with a better S/N than using only the lunar surface as a reflector. But I don't know. They might be a lot more precise than 1 degree.
: yeso; units
Currency exchange rates from FloatRates (USD base) on 2025-10-06
3749 units, 113 prefixes, 120 nonlinear units
You have: 2 arcsin(earthradius/moondist)
Unknown unit 'arcsin'
You have: 2 asin(earthradius/moondist)
You want: dms
1 deg + 53 arcmin + 57.540656 arcsecI don't know what wavelength they're using, but at 555nm, 1.22λ/d would be 0.193 microradians, which, unless I'm doing the math wrong, works out to a 74-meter Airy-spot radius at the distance to the moon. At that sort of size, you'd think the majority of the photons in the desired wavelength band would be from their laser rather than stray Earthshine.
I was doing calculations based on λ = 350nm and a 500-mm reflector, and no retroreflector, and getting rather sad estimates of 3 joules of light transmitted per returned photon (per receiver). While that's clearly a feasible commnications system, it's going to be pretty limited in bandwidth. I'm not sure if C-band radio is better?
There's a lot of math that goes into selecting the right bit-width for the signal, which I ain't doing here and now [0], but most 24dB things tend to be 32bit for reasons. The arrays here are a bit more, but probably fit that kind of channel.
Assuming 32bit and 30dBi, you'd be sending at roughly 20-30MHz, and receiving at about 1kHz. (Less if you hit bad weather.)
So... 1 bit per second. Not byte. Bit.
Point-to-point on the Earth would actually be semi-decent, as another comment pointed out.
It's 1.3 to 1.6 seconds each way to the moon, by radio link.
JPL's much, much, much bigger arrays can only achieve 64kbps.
Going beyond intuition- secondary reasoning says since GSO bandwidth & bitrate is acceptable for TV and sat phones by the hundred.
Tercheriary is we have/had a few hundred bps from Voyager II and that's a might bit further out than the moon, and it was called out that using an 80meter dish it could be pushed to a little over 1kbps- which means at some point inverse square becomes the only non-neglegiable factor.
So please, explain with something besides repeatedly saying "latency." Even if I'm wrong, they're strong enough counters to deserve more than a single word.
Or 31.25 million bytes per second if you prefer.
This would be for a point to point terrestrial link. OFDM probably wouldn't work for EME (at any power level).
12 V DC (≈1.5 kW peak)
PA looks suspiciously similar to SE5004L. I just needed some for my own projects but every distributor is out of stock. I wonder if this is where all of them went?
Wonder how they prevent usage as radar as this thing could pretty much be a drop-in missile seeker.
https://www.jpl.nasa.gov/news/radar-astronomy-used-to-resear... (1991)
gus_massa•3mo ago
cactacea•3mo ago
https://hamradio.engineering/eme-moonbounce-bouncing-signals...
http://www.g4ztr.co.uk/app/download/13284489/RaCcom_Feb14+EM...
http://www.g4ztr.co.uk/app/download/13300096/Radcom_Mar144+E...
dbcurtis•3mo ago
A long time ago I started collecting parts for a 432MHz EME system. Life got in the way and I never built it out. Good luck with your endeavor!
ErroneousBosh•2mo ago
A good ten years ago or more, they used Arecibo to transmit CW moonbounce on 70cm. I was able to receive it in my back garden with a handheld and an 11-element Yagi balanced on my clothesline ;-)
ErroneousBosh•2mo ago
If you're reasonably handy with simple hand tools you can build a moonbounce array for a couple of thousand and a month or so of evenings.
Polizeiposaune•2mo ago
The wikipedia article:
https://en.wikipedia.org/wiki/Stanford_Dish
links to:
https://web.archive.org/web/20201108114110/https://www.cia.g...
which has this tidbit which explains why it works as well as it does when it works:
"Fortunately for us, the moon appears only slightly rough to radio waves; most of the reflected energy comes back from an area at the near point just a few miles in diameter. The bulk of the energy striking farther around on the side is reflected out into space and never returns to earth."