[amsat-bb] Re: PSK v. APRS

Trevor . m5aka at yahoo.co.uk
Mon Jun 6 14:38:31 PDT 2011

My pet hate is AX.25 1200bps FM which every satellite seems to use, it uses too much bandwidth, too much power and has no forward error correction.

BPSK systems such as that to be used on ARISSat-1 can provide 1000 bps with error correction in less than 1/10th the bandwidth. 

But the reason AX.25 1200bps FM is still used for new satellites is because there's so much infrastructure, TNC's, PC software etc, already inplace, it's the easy option. 

Currently there is no single standard for sending data using BPSK not even the data rate is standardized. I believe the BPSK telemetry on FOX will use a different standard to ARISSat. FUNcube and UKube-1 will also use different versions running 1200bps and 9600bps respectively. 

Personally I think 9600bps BPSK will be the one to go for in the long term but none of these BPSK systems are flying yet. So until they are and are proven to work in space I think AX.25 1200 FM will continue to be used. 

Getting new equipment on the ISS has an incrediably long lead time and of course relies on someones goodwill to pay some $5,000 a kilo freight charges, so realistically I can't see any significant changes to the ISS equipment for sometime to come.

73 Trevor M5AKA

--- On Mon, 6/6/11, Greg Dober <almetco at comcast.net> wrote:
> Bob,
> Guess the APRS dilemma was like splitting the atom. 
> The real use and the
> unintended use.
> Could a system like the ISS be switched to a PSK31 or
> similar mode in the
> future?  How well would PSK work with Doppler
> etc?  I use it on HF, but was
> wondering if FM and satellites could be feasible.  I
> believe this was
> mentioned as possibly being part of Fox's system.
> 73
> Greg

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