highaltitude.log.20080217

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[08:44] <Simon-MPFH> What a stunning morning here in Staffycher. Sure wish I was releasing a balloon right now...
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[09:17] <Laurenceb> hey all
[09:26] <jcoxon> hey Laurenceb
[09:48] <Simon-MPFH> What a stunning morning eh folks?
[09:56] <jcoxon> shame its sooo cold
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[13:59] <edmoore> hi Laurenceb
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[14:01] <fnoble> hello
[14:03] <edmoore> hi fnoble
[14:03] <edmoore> just the man
[14:04] <edmoore> I know you're somewhat ahead of me on this one
[14:04] <edmoore> but have you looked at psk-31?
[14:04] <fnoble> yes, thats what i was saying about last sunday
[14:04] <edmoore> yes i seemed to remember, but was a bit tired :)
[14:04] <fnoble> not that i know *that* much about it
[14:05] <fnoble> but looks neat
[14:05] <edmoore> it looks kind of cool, and would be something different for us to work on
[14:05] <fnoble> should ask steve when he comes on
[14:05] <edmoore> yes
[14:05] <edmoore> psk would be a good thing to master for certain other lion-type projects
[14:05] <edmoore> sigh
[14:07] <edmoore> how are you doing?
[14:07] <edmoore> I'm looking forward to seeing this silkscreen :)
[14:09] <fnoble> not too bad, just about to email the order to olimex
[14:10] <fnoble> if you really want to see it, its in the svn
[14:10] <fnoble> :)
[14:10] <fnoble> do you have a credit card to order on?
[14:14] <fnoble> btw, you should update to libraries in the svn, as i have had to modify some of them to pass the drc
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[14:14] <fnoble> or just remove retarded features
[14:15] <edmoore_> sorry i missed all of that
[14:15] <fnoble> got d/c?
[14:15] <edmoore_> dodgy wireless in our bar
[14:15] <fnoble> ah ok
[14:15] <fnoble> want to just meet up? i can come up to you
[14:16] <edmoore_> yeah ok
[14:16] <edmoore_> sounds good
[14:16] <fnoble> only if your not too busy
[14:16] <edmoore_> nope!
[14:16] <edmoore_> not working for a bit now
[14:17] <fnoble> cool, see you in a sec
[14:17] <edmoore_> psk looks like quite a lot of analogue circuitry
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[16:21] <Hiena> Good evening!
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[17:48] <jcoxon> edmoore is alive!
[17:48] <jcoxon> how did it go?
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[18:39] <Hiena> Groan...I really miss my stolen hydrogen generator...
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[20:44] <Simon-MPFH> Anyone here familiar with pressure sensors like the MAX100AP?
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[21:48] <Laurenceb> hello all
[21:48] <Laurenceb> I've been looking into a spread spectrum type system
[21:50] <Laurenceb> it would work better than RTTY
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[21:57] <Laurenceb> if you use a pseudorandom spreader code, then the framing is handled by the deconvolution stage, so you dont need start and stop bits, and theres no risk of bit flip errors
[22:06] <Daviey> wth was just said :)
[22:09] <Laurenceb> bit slip* not bit flip sorry
[22:10] <Laurenceb> you'll always get bit flip errors :P
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[22:18] <Laurenceb> hi there
[22:18] <Laurenceb> RocketBoy: is it legal to transmit phase shift signals on 433MHz by using a transmission line arrangement?
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[22:20] <RocketBoy> I doubt it - you mean by taking the output of the transmitter phase shifting it (coax?) and mixing quadrature signals
[22:20] <Laurenceb> so have a 434MHz module, then a board with a transmission line arrangement and some transistors so it can generate modulated phase output?
[22:20] <Laurenceb> i.e. it wont be increasing the output power
[22:20] <RocketBoy> ?
[22:21] <Laurenceb> yes
[22:22] <RocketBoy> I doubt it as they seem quite picky about what you put on the anteena output
[22:22] <Laurenceb> but using striplines
[22:22] <Laurenceb> hmm looks like frequency modulation is the only way to go :(
[22:22] <Laurenceb> I've been thinking about a spread spectrum type scheme, using a pseudo random signal to modulate
[22:23] <Laurenceb> so to transmit at say 300 baud, it would be modulating at 2400 baud
[22:23] <Laurenceb> ie 8*300
[22:23] <RocketBoy> I'm not sure what problem you are trying to fix? FM seems more than good enough range wise - are you trying to get more throughput?
[22:23] <Laurenceb> yes
[22:24] <Laurenceb> and solve bit slip error problems
[22:24] <Laurenceb> with my experience it seems that bit slips can occur
[22:25] <Laurenceb> so if a start to stop bit transition is corrupted, it can cause an ongoing error condition
[22:26] <Laurenceb> the spread spectrum style scheme would give a bit more throughput, and eliminate bit slip errors, as the framing is provided by the pseudo random noise
[22:27] <Laurenceb> also it is more resistant to interference, which hasnt been a big problem, but its nice to make it more resistant
[22:27] <RocketBoy> well you probably would be better off with syncronus data - like packet radio - using the phase of the transisiions to lock the bit clock
[22:27] <Laurenceb> phase of the transistions?
[22:28] <Laurenceb> like manchester encoding?
[22:28] <RocketBoy> yep
[22:28] <Laurenceb> hmm ok
[22:28] <Laurenceb> I dont quite understand how to decode manchester
[22:28] <RocketBoy> thats where I was taking the radio system next (If I got the time)
[22:29] <Laurenceb> seems to me you could get an inverted signal...
[22:29] <RocketBoy> yeah - I'd have to look it up
[22:29] <Laurenceb> well manchester is sort of a really simple case of direct spread spectrum
[22:30] <RocketBoy> BTW - there is a relationship between FM and PM - you can generate FM using a PM modulator and a modified input signal
[22:30] <Laurenceb> the problem is that none of these schemes seem to be supported by programs like fldigi or gmfsk
[22:30] <Laurenceb> yes
[22:31] <RocketBoy> so the reverse (PM from FM) must be true
[22:31] <Laurenceb> so you would have to write your own
[22:31] <Laurenceb> hmm interesting point, but it would be hard to control I bet
[22:31] <Daviey> Laurenceb: manchester encoding isn't too bad
[22:31] <RocketBoy> use packet radio - it has manchester coding built in
[22:32] <Laurenceb> yes, but there arent sound card applications for it?
[22:32] <RocketBoy> TrueTTY will dicode packet radio
[22:32] <Laurenceb> ah ok
[22:32] <RocketBoy> and some others
[22:32] Action: Laurenceb cant get TrueTTY to talk to his sound card
[22:32] <Laurenceb> I'll probably get a USB one
[22:33] <RocketBoy> perhaps you need to introduce your PC to Mr hammer#
[22:33] <Laurenceb> I'll look at packet radio, is it fexible
[22:33] <Laurenceb> ie can you change the baud rates ect?
[22:34] <RocketBoy> I think the main problem will be that packet radio (mostly) uses AFSK - there you modulate audio tomes which are then carried over the radio link
[22:34] <Laurenceb> but with SSB thats what we get?
[22:35] <RocketBoy> the result is quite wide band hence not good for range
[22:35] <Laurenceb> sure, but we get AFSK from the scanner
[22:35] <RocketBoy> I got about 30Km on 10mW of AFSK
[22:35] <Laurenceb> I remember
[22:36] <Laurenceb> but if we use the RTTY scheme, we are decoding AFSK at the ground
[22:37] <Laurenceb> so we could modify the firmware on the TX and use a packet radio decoder?
[22:37] <RocketBoy> no the SSB is different its transmitting FSK
[22:37] <Laurenceb> sure, thats what its transmitting, but the audio into the sound card is AFSK
[22:37] <RocketBoy> its one step more direct
[22:38] <Laurenceb> surely te actualy waveform into the soundcard is the same?
[22:39] <RocketBoy> sure they sound the same to the ear becuse you listening to FSK using SSB and AFSK using FM
[22:39] <RocketBoy> but spectrum wise they are different.
[22:40] <RocketBoy> also with AFSK/FM the tones are accurate (and could be used for clock timing in themselves)
[22:40] <Laurenceb> radio spectrum wise, but not into the sound card, and thats what the software sees
[22:40] <Laurenceb> right
[22:40] <Laurenceb> ok
[22:40] <Laurenceb> I've got to make a phone call, back in 30 min
[22:40] <RocketBoy> with FSK/SSB the tones are set by the shift and reciver tuning
[22:40] <Laurenceb> yes
[22:40] <Laurenceb> bbl
[22:41] <RocketBoy> bbl2
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[00:00] --- Mon Feb 18 2008