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.

73

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 <vk5qi@rfhead.net>
To: nick <quadpugh@bellsouth.net>
CC: Pete (vk2pet) <vk2pet@internode.on.net>; AMSAT BB <amsat-bb@amsat.org>
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. 

73
Mark VK5QI

On Wed, Apr 20, 2022 at 6:29 PM nick <quadpugh@bellsouth.net> 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
 
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