highaltitude.log.20081229

[00:00] <SpeedEvil> I.E. I have a 18MHz bitstream of 1 bit samples of a 1.023MHz IF.
[00:00] <Laurenceb> what frontend?
[00:01] <SpeedEvil> How can I in the least CPU cycles go from this to a I/Q output at 1KHz per satellite.
[00:01] <Laurenceb> that sounds a bit odd
[00:01] <SpeedEvil> max something
[00:01] <Laurenceb> most stuff is direct conversion
[00:02] <Laurenceb> so the IF ~0Hz
[00:02] <SpeedEvil> yeah
[00:02] <SpeedEvil> But this is $4 :)
[00:02] <Laurenceb> so take the SE4120
[00:02] <Laurenceb> oh
[00:02] <Laurenceb> where?
[00:02] <SpeedEvil> The chip I mean
[00:02] <SpeedEvil> in relatively small qty
[00:02] <Laurenceb> yeah, which chip?
[00:02] <Laurenceb> Maxim?
[00:03] <SpeedEvil> http://www.maxim-ic.com/appnotes.cfm/an_pk/3447
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[00:06] <Laurenceb> I see
[00:06] <Laurenceb> with the SE4120 thats all in one IC
[00:06] <SpeedEvil> I'm trying to make it fit in with my existing design, for a small thing to sell on ebay, as it'd add stuff.
[00:06] <Laurenceb> yeah
[00:07] <Laurenceb> I guess I just like the idea of direct downconversion, but that looks good
[00:08] <Laurenceb> it may be a bit easier to process, as theres hopefully less complex numbers involved
[00:08] <SpeedEvil> As far as I can see, the 4120 is essentially the same, with the addition of multi-bit output
[00:09] <SpeedEvil> 'Specifically designed for GPS applications, the SiGe SE4120 receiver IC integrates a low-noise amplifier (LNA), a low IF receiver, linear automatic gain control (AGC), IF filter, image reject mixer and an advanced multi-bit I/Q analog to digital converter (ADC).'
[00:09] <Laurenceb> its also 38kHz IF
[00:09] <Laurenceb> and IQ output
[00:09] <SpeedEvil> Umm
[00:09] <SpeedEvil> 38KHz?
[00:10] <Laurenceb> basically direct downconversion
[00:10] <SpeedEvil> wacky
[00:10] <Laurenceb> well itmakes the sat frequency always positive
[00:10] <SpeedEvil> I suppose that will keep the lowest doppler away from 0.
[00:10] <Laurenceb> yeah
[00:11] <Laurenceb> did you see my aquisitions with the SE4120?
[00:11] <Laurenceb> just a sec... they may be on another machine
[00:12] <SpeedEvil> no - I diddn't.
[00:12] <SpeedEvil> My code isn't at that stage yet.
[00:12] <SpeedEvil> Owing to being at the moment of the timed psuedocode variety.
[00:13] <SpeedEvil> And being in pencil on A4 :)
[00:13] <SpeedEvil> Have you gotten to the state of extracting navigation messages?
[00:15] <Laurenceb> nope
[00:15] <Laurenceb> just aquisition
[00:16] <SpeedEvil> how much was your reciever?
[00:19] <Laurenceb> £150 about
[00:19] <Laurenceb> from sparkfun
[00:19] <Laurenceb> http://imagebin.org/34519
[00:19] <SpeedEvil> oh - that one
[00:19] <Laurenceb> thats all I've got here
[00:19] <Laurenceb> just the raw spectrum
[00:19] <Laurenceb> the lines are from my laptop
[00:20] <Laurenceb> probably clock line harmonics of the motherboard
[00:20] <Laurenceb> total width is 8MHz
[00:21] <SpeedEvil> :)
[00:21] <Laurenceb> theres a 4MHz mode as well
[00:22] <Laurenceb> and a filter for 4MHz bandwidth or 2
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[00:22] <Laurenceb> for GPS L1 or Galileo L1 which is BOC
[00:25] <Laurenceb> http://pastebin.com/m79915ab4
[00:25] <SpeedEvil> how many sats were you picking up?
[00:26] <Laurenceb> http://pastebin.com/m23ece4d8
[00:26] <Laurenceb> 4 or 5
[00:27] <Laurenceb> you need the last bit of code to generate the PRN
[00:29] <Laurenceb> that code just finds some sats and plots them in doppler/code space
[00:33] <SpeedEvil> Not really reading it - fft is some orders of magnitude over my CPU spec :)
[00:34] <Laurenceb> I like the idea of batch processing over loops
[00:34] <SpeedEvil> I think I can do some batch processing using SIMD techniques
[00:34] <edmoore> it's certainly much friendlier with PC OSs
[00:34] <SpeedEvil> to a useful degree anyway
[00:34] <Laurenceb> the usual technique is to do FFT < realtime
[00:35] <Laurenceb> then use the results to setup the loops
[00:35] <Laurenceb> but I like the idea of FFT running on a fpga at 1Khz
[00:35] <Laurenceb> its just groovier :P
[00:35] <SpeedEvil> there is also the 64000 little correlators approach to brute force.
[00:36] <SpeedEvil> (though in practice you wouldn't use 64000 - as it's an utter waste due to the slow clock rate)
[00:36] <Laurenceb> if you want something that doesnt need finnicky setup, fft is optimal
[00:37] <Laurenceb> correlators always needs the cpu thats running the show to have some background process running to do reaquistion
[00:37] <Laurenceb> although on a balloon/rocket
[00:37] <SpeedEvil> True. I don't see anything especially complex about the other way. It's just annoying CPU limitations is all.
[00:37] <Laurenceb> its not a big problem
[00:37] <Laurenceb> as theres not obsticals to block out the sats
[00:37] <SpeedEvil> Well - if you don't have a master clock, you're in trouble on any GPS
[00:38] <Laurenceb> sure... whats that got to do with it
[00:38] <SpeedEvil> If you want to be able to re-lock fast
[00:38] <Laurenceb> anyway I'm off, cya all
[00:38] <Laurenceb> yeah
[00:38] <SpeedEvil> night
[00:38] <Laurenceb> but even with the best TCXO, you need to do some work to relock after say 2 seconds
[00:38] <Laurenceb> I'm off
[00:38] <SpeedEvil> Well - no.
[00:38] <SpeedEvil> At least according to some numbers I did.
[00:38] <SpeedEvil> But later.
[00:38] <SpeedEvil> wave
[00:39] <Laurenceb> yeah
[00:39] <Laurenceb> maybe 2S is doable
[00:39] <Laurenceb> anyway sleep
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[09:26] <edmoore> morning all
[09:26] <edmoore> jcoxon: in the dinium?
[09:27] <jcoxon> morning edmoore
[09:27] <jcoxon> yup
[09:27] <jcoxon> back in a cold flat
[09:27] <jcoxon> still wearing my coat
[09:27] <jcoxon> wrestling with your tinternet?
[09:28] <edmoore> hope it will be fixed soon
[09:29] <edmoore> there are too many potential projects
[09:29] <jcoxon> hehe
[09:29] <jcoxon> pick one and go for it!
[09:30] <jcoxon> what you thinking?
[09:32] <edmoore> well automatic tuning units for antennas are too expensive
[09:32] <edmoore> but not desperately complex in principle
[09:32] <jcoxon> :-)
[09:32] <edmoore> it would be a really cool open source hardware project, that's all
[09:33] <jcoxon> it doesn's already exist? I'm suprised
[09:33] <edmoore> would google but...
[09:34] <edmoore> you'd basically have to build the adjustable matching network, then build the microcontroller bit such that it's compatible with as many protocols as possible (icom, yeasu etc)
[09:34] <jcoxon> do you want an ssh account?
[09:34] <edmoore> so the openess lends itself as people with the right kit can add their ptorocols
[09:34] <jcoxon> yeah
[09:35] <edmoore> i could actually try an alternative accoun t
[09:35] <edmoore> if you've one going spare
[09:35] <edmoore> might have just been unlucky so far
[09:36] <edmoore> guys are currently doing fm USA to australia on 10W atm
[09:36] <edmoore> apparently good conditions
[09:37] <jcoxon> guys?
[09:37] <edmoore> hams
[09:37] <jcoxon> oh right
[09:39] <jcoxon> you can either have a linux shell or a mac os x shell
[09:39] <jcoxon> your choice
[09:39] <edmoore> no pref
[09:39] <edmoore> go for linux
[09:39] <jcoxon> yeah
[09:39] <jcoxon> one sec
[09:42] <edmoore> nothin doin just yet
[09:43] <jcoxon> not working?
[09:43] <edmoore> jcoxon: does 5secs on 'open antenna tuning unit' reveal anything on google?
[09:43] <edmoore> not working
[09:44] <jcoxon> as in you can't login to the account?
[09:44] <edmoore> i can login
[09:44] <edmoore> but the socks forwarding isn't doing much
[09:44] <edmoore> socks to natrium's server
[09:44] <jcoxon> oh yeah i feared that
[09:45] <jcoxon> quite possibly they've locked it down on that server
[09:45] <edmoore> mmm
[09:45] <jcoxon> what command are you using for hte SOCKS stuff
[09:47] <jcoxon> i've had a quick search - nothing really on auto tuner plans
[09:55] <edmoore> jcoxon: sorry, was absuing a croissant
[09:55] <edmoore> ssh -f zeusbot@[the-url-you-gave-me] -L 8080:72.136.18.113:8080 -N
[09:56] <edmoore> then in system prefs, socks proxy is localhost:8080
[09:56] <jcoxon> hmmm, okay
[09:56] <jcoxon> and not working
[09:57] <jcoxon> i've got to dash off to fix my grandfather's 'puter
[09:57] <jcoxon> so sadly can't work it out
[09:57] <jcoxon> you are welcome to vnc into my old apple if you want
[09:59] <edmoore> ok
[10:00] <edmoore> can we try that?
[10:00] <jcoxon> yup
[10:00] <jcoxon> one sec
[10:00] <jcoxon> let me configure the router
[10:00] <edmoore> awesomeness
[10:02] <jcoxon> do you have a vnc viewer?
[10:02] <edmoore> i think i have chieck-of-the
[10:02] <jcoxon> yeah
[10:02] <jcoxon> cool
[10:02] <edmoore> chicken*
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[10:14] <jcoxon> hey ed
[10:15] <jcoxon> edmoore,
[10:15] <edmoore> yo
[10:15] <jcoxon> right you've got ssh access and vnc access to it
[10:16] <jcoxon> you getting pm's?
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[10:47] <jcoxon> hey all, back
[10:57] <jcoxon> hey G8KHW,
[10:58] <jcoxon> do you by any chance have a copy of the 2007 logs? seem to have disappeared during a server move at some time
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[11:09] <rjharrison_> Morning all
[11:10] <rjharrison_> Any one want to offer me 80k pa to build hab balloons?
[11:10] <rjharrison_> It's a lot more fun thatn the day job
[11:11] <jcoxon> haha
[11:11] <jcoxon> morning rjharrison_
[11:24] <edmoore> morning rjharrison_
[11:24] <edmoore> high altitude golden handcuffs
[11:24] <jcoxon> how cool would a supermarket sweep in sparkfun be
[11:24] <jcoxon> if only
[11:25] <edmoore> hahaha
[11:25] <edmoore> what an idea
[11:25] <edmoore> I'd be straight to the gps and telits
[11:25] <edmoore> some good dollar density there
[11:25] <jcoxon> yeah thats what i was thinking
[11:25] <jcoxon> also tilt compensated compasses
[11:25] <jcoxon> imus
[11:25] <edmoore> and maybe grab the filling in form for their R&D pcb manufacturing
[11:25] <edmoore> unlimited gold phonexing
[11:26] <edmoore> i shouldn't verbify (what is the actual word for that?) gold phoenix
[11:28] <jcoxon> edmoore, when are you back to cam?
[11:28] <edmoore> not sure
[11:28] <edmoore> something approximating the 10th
[11:29] <edmoore> definitely will be around for robert's launch
[11:30] <edmoore> might splash out on a 70cm yagi for then too
[11:30] <edmoore> unless I can find some nice bits at the scrappie to make one
[11:30] <jcoxon> i think rjharrison_ is thinking this weekend
[11:30] <edmoore> G8KHW: would using steel elements have a significant detrimental effect on an antenna?
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[11:31] <edmoore> fine, be like that
[11:31] <jcoxon> haha
[11:33] Action: jcoxon is reinstalling windows xp
[11:33] <jcoxon> i hate windows - so messy
[11:35] <edmoore> agreed
[11:35] <edmoore> and you think 'this is the best they have to offer' and it's sort of 2001
[11:35] <edmoore> with only a few changes since
[11:35] <jcoxon> and vista is even worse
[11:35] <edmoore> exactly
[11:35] <jcoxon> was setting up my dad's laptop yesterday
[11:35] <jcoxon> urgh
[11:36] <edmoore> I love the start
[11:36] <edmoore> whoops
[11:36] <edmoore> this will sound pretencious - but i love the opening of the 1st movement of rach's 2nd concerto
[11:37] <edmoore> a few big chords and then he's like 'oh shit, I haven't warmed up enough - strings- cover me for 2 minutes'
[11:37] <jcoxon> i was worried you were going to say: "i love the start... ...button"
[11:37] <edmoore> and he just does some arpeggios whilst the strings blast you with melody
[11:37] <jcoxon> considering we were discussing windows
[11:38] <edmoore> we're discussing rachmaninoff now
[11:38] <jcoxon> i know
[11:38] <edmoore> for some value of 'we'
[11:42] <jcoxon> hmmm i need to repair my gm862-gps module
[11:42] <jcoxon> broke the sim card holder bit
[12:16] <Laurenceb> http://www.flickr.com/photos/fotoopa_hs/3103153894/in/set-72157611107153997/
[12:17] <Laurenceb> SpeedEvil: thats interesting
[12:17] <Laurenceb> but you have to consider the allen variance
[12:18] <Laurenceb> I think art of electronics has a very nice section on this
[12:19] <jcoxon> bbl
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[12:19] <Laurenceb> I cant remember offhand what that meas for the stability over a timescale of a few seconds...
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[12:22] <Laurenceb> I'm off
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[18:53] <corstan> hello
[18:53] <corstan> anybody?
[18:53] <SpeedEvil> hello
[18:54] <corstan> I have connected the gm862 to gumstix (verdex, gpsstix and netstixSD)
[18:54] <corstan> how do I communicate with gm862
[18:54] <SpeedEvil> I vaguely recall it's got several serial modes.
[18:54] <corstan> I have tried using kermit on /dev/ttyS1
[18:54] <SpeedEvil> you may need to strap certain pins low/high
[18:54] <corstan> and I can type and all
[18:55] <corstan> but I can't do AT and then receive OK
[18:55] <corstan> should I try gnokii?
[18:55] <SpeedEvil> I don't know.
[18:55] <SpeedEvil> try connecting pins 2 and 3 of the serial port, and see if it loops back
[18:56] <corstan> it is connecting
[18:56] <corstan> that's the reason I can type in kermit
[18:56] <corstan> but I need a command line based tool to send and receive SMS
[18:56] <SpeedEvil> If you can't get any response to 'AT<return>' then SMS won't work
[18:57] <corstan> don't I need to type in my PIN for the SIM card etc. ?
[18:57] <SpeedEvil> at some point
[18:58] <SpeedEvil> but the modem should respond in some way before that
[18:58] <SpeedEvil> read the programming manual - I forget what it's called for the module
[18:58] <SpeedEvil> But if you're connected at the correct baudrate, and serial is enabled, and everything is powered right, you should get some sort of response
[19:05] <corstan> I can type in kermit
[19:05] <corstan> that's all I get
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[20:17] <natrium42> hehe, i have written such a tool just the last week :P
[20:18] <natrium42> didn't want to use overcompex thing like gnokii
[20:33] <jcoxon> oops i missed him
[20:33] <jcoxon> he really needs to tie down DTR to ground
[20:33] <jcoxon> oh well
[20:33] <jcoxon> cya
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[22:17] <Laurenceb> hello
[22:20] <Laurenceb> oh messages
[22:20] <Laurenceb> SpeedEvil: yeah looks like the allen variance is a small effect - http://www.gmat.unsw.edu.au/snap/gps/gps_survey/chap1/132.htm
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[00:00] --- Tue Dec 30 2008