Hi everyone,

After a busy week (including ANZAC day here in Australia) I will go & ready all your reply’s.

Thanks to everyone that have taken the time to have there say in what I will call a ‘debate’ of pros & cons of Tiny GS.

Regards

Pete

VK2PET

From: Samudra Haque [TTLLC] <[email protected]>
Sent: Saturday, 23 April 2022 23:15
To: David G0MRF <[email protected]>; [email protected]; [email protected]
Cc: [email protected]; [email protected]
Subject: [AMSAT-BB] Re: Tiny GS

Hello, pardon my lengthy article here, I don’t engage regularly. The discussion of use of proprietary, closed comm systems in ham bands, struck a chord, since I am aware of the great efforts by Open Research Institute (US) to bring M17 comm systems for broadband service in the amateur-satellite arena. This is exemplary compared to paying $$$$ for commercial products, or to help commercial companies get footholds into future markets. I question – whether ICOM/Yaesu/others – if the amateur-satellite community gets any benefit from them to use their software/hardware products, such as radios/etc., that may be donated (the company gets a tax credit) or purchased (so they are being paid for this stuff)? I’m from the years of DIY ham radio !

Anyway, I published around 2011-2012 technical articles about multi-hop interplanetary relay communications. I studied Ka-band service based upon the published specs of the Mars Rec. Orbiter, which was then already on-mission. My target data rate was 1 Gbps full du-lex, persistent, across planetary orbit geometries whether from a ground station or from a orbiter or in between, including flyers. Then I discovered CubeSats, and made designed, developed and delivered a propulsion system for CubeSats (BRICSAT-P, CANYVAL-X missions).

But I was surprised that communications systems for small satellites were (in my opinion) relegated to an after-thought – even though, in the commercial VSAT industry small form IDU/ODU/SSPA/HPA and compact stowable antennas have been around for quite a while, and they are becoming smaller and smaller! So we could also use the parts – as we like.

I was also impressed with my late mentor Bob Bruninga’s PSAT / APRS comm relay experiments and experience, and the simplicity of what he showed, that it can be done – ground to space to space to ground relay ! which I studied ..

I do see very expensive hardware being offered for sale on various websites for “high bit-rate” communications – that do require a matching ground station and coverage. In a past technical analysis for university near El Paso, TX, I calculated that the slew rate of the antenna for the projected high eccentricity orbit of a satellite would have literally torn the bearings off the king post for a parabolic dish. So electrical steering would be better of in that case, but then it doesn’t solve all of the problems. All for a few kilobits of power constrained communication from beyond the radiation belt.

** Would there be a community interest in having a forum-style panel discussion on better/modern/practical high bit-rate, deep space comms architecture for ham purposes – global in scope, not only US – that the community could propose for developers to test/study/learn and adopt?

** Perhaps even a virtual AMSAT-sponsored technical forum inviting open-practitioners? Perhaps even considering innovation in multi-hop relay comms architectures, better coding mechanisms (open-source, open-licensed but allowing commercial levels of support for the developers if they provide continuing maintenance for long duration) and better prototype reference designs (again, allowing commercial levels of support for the design maintenance)?

I say the “commercial levels of support” because there are plenty of software / hardware projects that have been abandoned due to lack of proper support after they have been released, or as the developer has moved on/passed away – e.g., EZNEC style programs, many shareware products, many prototype software products, many schematics that have never been able to be updated after the technology was obsoleted. And oh by the way:

(my thoughts) How many times do we have to reinvent the wheel? Students have four years in undergraduate, 1.5 years in MS programs, and by the time they attempt a Ph.D., they are industry/academia bound and we can’t rely upon their interest/support to maintain healthy R&D activity in the amateur-satellite field – they join industry and we end up with having to explain to managers at various companies, “Have you heard of AMSAT, those people who design satellites .. ?”

And lastly I would like to volunteer to help in the architecture definition of a multi-hop amateur=satellite radio/optical network for long duration missions and innovation in space.

73 de Samuda N3RDX

From: David G0MRF via AMSAT-BB <[email protected]>
Sent: Saturday, April 23, 2022 8:50 AM
To: [email protected]; [email protected]
Cc: [email protected]; [email protected]
Subject: [AMSAT-BB] Re: Tiny GS

HI Mark.

Only just spotted this.

The 4 Funcube satellites have not used FEC or fast data rates on their command uplink. We only need to send fairly simple commands or the odd 256 character text message for educational outreach etc.

Also, the ground stations can run as much power as we like.....So no problems with the uplinks.

The downlink is a completely different story. All the satellites (UKube-1 now QRT) use a modified version of Phil Karns error correcting code originally developed for AO-40.

As Phil has told us, this is not an ideal solution, but it does work very well and it is documented. The satellites transmit telemetry continuously. We wanted to get away from the troublesome short burst of data every few minutes that can be difficult to track. Instead The satellites use BPSK generated in a passive mixer....A mini Circuits RMS-1 from memory. 400mW can be received with a simple turnstyle, the low power 50mW or even 30mW can be received without problem using a typical LEO pack type antenna. Bit rate is 1200bps. Telemetry is generated in and 'old' 8 bit processor. TX band is 2m which helps with the path loss.

If you watched any of the AMSAT-UK colloquium presentations last October, you may have seen that a couple of very capable students from Surrey University have produced a modern version using a low power STM32 processor. They managed to increase the bit rate upto 100kb/s and incorporate the whole thing into a real time operating system.

All we need now is some time on 'Funcube Next' and we may be able to get it into space.

David G0MRF

However, you are in the right place to ask the question - perhaps the engineers of the Fox-series of sats, or Funcube could comment on their uplink systems. With modulations like BPSK and decent FEC, extremely good performance is definitely possible, but no - we can't make you a single chip to do it. Sorry about that.

-----Original Message-----
From: Mark Jessop <[email protected]>
To: nick <[email protected]>
CC: Pete (vk2pet) <[email protected]>; AMSAT BB <[email protected]>
Sent: Wed, 20 Apr 2022 9:52
Subject: [AMSAT-BB] Re: Tiny GS

Can I point at a single-chip device that can do that? Not off the top of my head, no.

You'll note that amateur radio operators don't generally have access to silicon foundries, so making this kind of thing is a bit difficult.

However, you are in the right place to ask the question - perhaps the engineers of the Fox-series of sats, or Funcube could comment on their uplink systems. With modulations like BPSK and decent FEC, extremely good performance is definitely possible, but no - we can't make you a single chip to do it. Sorry about that.

As for the specs you quoted, I'd be seriously testing that out on a bench before you trust what is said in the datasheet. Factors like frequency offset (due to doppler shift, or crystal drift) are also going to come into play here. You'll note that the other users of LoRa on sats are running at very wide bandwidths (125 kHz... for maybe a few hundred bit/s throughput... what an efficient use of spectrum!), so I'd be asking why that is the case.

Mark VK5QI

On Wed, Apr 20, 2022 at 6:29 PM nick <[email protected]> wrote:

Good morning/afternoon Mark

Good questions. The main reason for choosing LoRa. The main reason for choosing LoRa is its receiver sensitivity which is -148 DBM. This let us a use a $6 device on a LEO satellite close the link with an omni gain antenna on the ground. This can be done in a 10 KHZ channel. I also believe this can be used in part 97 of the FCC rules. It might require a rule waver but I believe it is doable.

The negative is as you point out is it is proprietary however there are 10 of million of the devices in operation globally.

In summary given it sensitivity and low cost it is a good choice.

Can you suggest a better choice ?

nick

Cell 337 258 2527

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