Gateway 10GHz Receive Station for JAMSAT

Let’s talk 10GHz amateur receive station for lunar orbit (Gateway).

JAMSAT (and others!) would like to see a prototype by JAMSAT’s next Symposium. I volunteer to follow through on this, bring it to them, and to remove whatever roadblocks are in the way.

Let’s see what we all can do together to achieve this goal.

Working from what we know of the Gateway amateur radio station through ARISS presentations at AMSAT-NA Symposium, here is the (developing) link budget and the beginning of requirements and specifications.

I can’t think of a better community to provide feedback. I hope that this station could be fully SatNOGS compliant? This could help expand the frequency range to microwave, which I know is a goal.

Free space path loss to moon is 224.5dB at 10.45 GHz.
2m dish with 80% efficiency is 46dB gain.
100 Watts transmit power at Gateway (very preliminary number)
With no other gains or loss that is -128.5 dBm.

Typical received signal power from a GPS satellite is −127.5 dBm

Someone smarter than me please check the work.

Mechanical
Az/El antenna rotator hardware.
Capable of pointing a 2 meter dish with associated receiver electronics.
All open source.
When possible, standard, easily sourced components should be used.
Movement speed capable of tracking LEO satellites.
Appropriate enclosure for protection from weather and spray.
Quiet enough to not disturb neighbors.

Electrical Control System
Should interface with on/off, DC Drive, or Stepper motors (perhaps with optional hardware add-ons).
Should accept position feedback from analog sensors, homing switches, or encoders.
Capable of running open-loop or closed loop (preferred).
Optional capability for position sensing through IMU.
Optional GPS for location and time sync.
Supports control by hamlib, common serial rotor protocols, N1MM rotor protocol, and additional networked methods such as MQTT.

We expect to accommodate a 3 inch steel mast.
A 2m dish is expected to provide enough gain.
There is a raspberry pi hat rotor controller schematic in progress.
There is a rotor design in progress.
We expect to use an SDR with filters and GNU Radio to demonstrate.

Tests expected with the DL0SHF Moon Beacon at 10,368.025 MHz.
http://moonbeacon.dl0shf.de/

EME operators in the San Diego Microwave Group will be consulted today at their monthly meeting.

Stability and pointing are challenges, but given the number of successful 10GHz EME stations, these challenges can be overcome. Eventual goal is an open source kit.

Repository: https://github.com/sconklin/openrotor

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Hey!! Nice!! We are designing a universal controller in order to replace the commercial rotator controllers. You may consider it as a choice for your rotator. I would like also to ask, is there any specific reason the rotator controller is based in raspberry pi (pi hat)?
Why not using a MCU that only control the rotator (like SatNOGS controller)?

Also I can help with the mechanical design of the rotator.

:beers:

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Thank you so much, and we’ll take you up on your offer!

We want to use as many parts as possible from the automotive industry since they are widely available and are sourced for decades. We have a Tormach PCNC 440 machine, a manual lathe, and a 3d printer fully available. There’s five of us willing to build things so far, but we’re hobbyists at mechanical design, not professionals.

The volunteer doing the pi hat rotor controller chose that because they already had a head start on it and a large amount of comfort and familiarity. They had a demonstration up at Hamvention in 2017 and got some good feedback. I will take this question back to them and see if we can converge.

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The reason for choosing a pi is for direct access to networked protocols during prototyping. The volunteer wants to build in a hardware WDT into the design to stop the motors if we lose the control loop.

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Linking the S-band station thread here as it is all relevant, just a different dish feed.

As to pi/arduino, I’m not 100% sure if this is what was going to run on the universal controller (@azisi?) but the K3NG rotator controller arduino code is quite universal and probably covers all of our needs, including PWM in the other thread. The arduino presents itself as an easycomm or yaesu rotator, works well with hamlib and other applications. I would personally opt for a microcontroller at that level, so we aren’t having to keep up with raspbian releases, possible deprecation, SD card issues, security, etc.

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Hey!

Why do you need direct access to networked protocols during prototyping?
By using MCU and K3NG you can use ethernet.

We need to develop the SPWM method to produce variable frequency sine wave to control for example yaesu G5500 (AC motors). I think that K3NG rotator controller arduino code doesn’t use any PID controller.

:+1:

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Thank you so much, this is very helpful.

I’ve gotten a lot of feedback about user expectations for controllers over the past week or two. All comments are going to the volunteer leading the controller effort.

For mechanical design, we are starting with Toyota Camry wheel bearings, hubs, and rotors. Stepper motors, shaft encoder, possible re-using some frame parts, and some machine shop time round out the basic structure.

The first draft will be clunky and nonstandard. The goal is inexpensive, very heavy duty, and repeatable. Toyota Camry parts are plentiful and available globally, but that shouldn’t be a restriction if the recipe works.

There’s some prior art here, literally, from several Burning Man projects and at least one very odd structure in East County San Diego that uses essentially the same idea (automotive parts) to mount a old heavy pan and tilt camera.

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I would like to follow the mechanical development, but it seems there is no activity on the github site…

So far it’s been conference calls and whiteboard. I’ll put the photos and notes up. I made the first order of flange bearings about an hour ago, so your timing is excellent :+)

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Hey! I just read the notes. Nice idea the combination of timing chain and e-brake instead of a worm gear box. What kind of brake will you use? Have you consider if the timing chain is it noisy? Maybe it is better to use a timing belt.

I’ve been trying to follow the open rotor mechanical design, but there isn’t much info, really. I will note that those “zoro” bearings are NOT “functionally equivalent” to wheel bearings. Are they adequate for the task at hand? Probably (don’t really know where they are going) - but automotive wheel bearings are significantly more advanced than those.

Thank you for the input! I concur. Wheel bearings are different. I bought these and adopted a 2m dish in order to try and size and gear the stepper motors. These were 1/5 the cost of new wheel bearings, so seemed like a good intermediate or bridge part.

We found another great source of wheel bearings in the Kart racing supply chain.

We have time this weekend to lash things together. One of us wants to try using auto timing chains or belts, but I haven’t seen how that ratio would work yet.

You are right, timing chains will indeed be noisy! :loud_sound:

We don’t want it to be so noisy that neighbors complain, but there are timing belts too. They are much quieter, but may require a lot more mechanical tension to stay working. Not sure on what kind of brake yet - there are some generic parts I’m learning about from Toyota that seem compact and cheap, but would require more fabrication than I am confident in doing.

Should know a lot more after this weekend.

Heh, the fabrication part is what I’m itching to try. As far as noise, timing chains are designed to run at crank velocities of up to almost 10k rpm. My two subaru’s currently use timing chains and noise is a non issue. I suspect we’ll be dealing with much lower drive RPM - I don’t think noise will be an issue. As far as ratios - McMaster offers hundreds of options for pulley diameters and belt styles, as well as sprocket diameters and chain styles. It may even be cheaper to use off-the-shelf commercially available stuff as opposed to having to raid salvage yards for suspect components. Many yards won’t let you crack open an engine to swipe the timing chains, either… and removing the drive pulleys (or sprockets) will often involve a puller. No problem for somebody like me, but if you haven’t spent half a lifetime collecting specialty automotive tools - might be a bigger problem.

Thank you for the reassurance and welcome aboard for fabrication involvement! Your advice is appreciated.

I’ve used timing chains for an art project, and the noise got complaints, but the expectations were a bit stringent.

The u-pull it yards here let you take whatever you can carry out, but doing that definitely doesn’t scale, as you have pointed out. We will save those field trips for bling like old gauges, bling, and maybe wiper motors.