highaltitude.log.20090415

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[07:25] <natrium42> yo jcoxon
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[07:27] <jcoxon> hey natrium42
[07:32] <jcoxon> hows it going?
[07:36] <natrium42> good, have been working on a solidworks model for a plastic enclosure
[07:36] <natrium42> how are you?
[07:37] <jcoxon> not bad thanks
[07:37] <jcoxon> lots of work for some reason
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[08:07] <mc-> jcoxon,need any help on the ballast system?
[08:08] <jcoxon> hey mc-
[08:08] <jcoxon> ummm not at present
[08:08] <jcoxon> putting together a flight computer for teh mission
[08:09] <jcoxon> once thats done will look into the ballast bit of it
[08:09] <mc-> was thinking of sending dump commands by radio
[08:10] <mc-> would be a good test for 2 systems
[08:11] <jcoxon> but also its not a tested system
[08:12] <jcoxon> so its an extra thing to go wrong
[08:13] <jcoxon> i was thinking a simple logic for dumping ballast would be a good start
[08:13] <jcoxon> i first want to test the flight computer without ballast on a 'latex floater'
[08:20] <jcoxon> bbl
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[10:02] <Laurenceb> hello
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[10:38] <shellevil> Laurenceb: pcb does airwires
[10:39] <shellevil> you can write a netlist in vi :)
[10:40] <shellevil> #Injector 1 driver - pwm io through driver
[10:40] <shellevil> PWM0-1 U1-21 R30-2 U7-2
[10:40] <shellevil> #Injector 2 driver - pwm io through driver
[10:40] <shellevil> PWM0-1 U1-22 R31-2 U7-4
[10:40] <shellevil> ...
[10:41] <Laurenceb> so PWM0-1 is the name for U1-22 ie pin22?
[10:41] <Laurenceb> and its routed to R31-2 ie U7-4 so pin 4 ?
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[10:42] <shellevil> track-name, then all the pins it's connected to
[10:44] <Laurenceb> I came up with a new architecture - lna -> ADL5387 -> I and Q signal lines through ~22MHz lowpass -> mixers on I and Q -> lowpass and amplify -> ADC
[10:44] <Laurenceb> or something like that....
[10:45] <shellevil> mixers to make an IF?
[10:45] <Laurenceb> the problem is with direct conversion you have noise around DC - caused by clock jitter
[10:45] <Laurenceb> yes
[10:45] <shellevil> yeah
[10:45] <shellevil> clock jitter and 1/f
[10:45] <Laurenceb> so you do direct conversion to an IF
[10:45] <Laurenceb> then convert the seperate I and Q channels down
[10:45] <Laurenceb> so you avoid image problems
[10:46] <Laurenceb> I'm still trying to work out if direct conversion will give decent results
[10:47] <Laurenceb> - GPS direct conversion ICs work ok, so its possible
[10:48] <shellevil> Or you just use a couple of 455KHZ IF cans.
[10:49] <Laurenceb> cans?
[10:51] <shellevil> the things you find in radios
[10:51] <shellevil> or did
[10:51] <shellevil> 455KHz IF filters
[10:52] <shellevil> with a little tuning screw at the top
[10:53] <Laurenceb> LC filters?
[10:54] <shellevil> yes
[10:55] <shellevil> http://hem.passagen.se/communication/ifcan.html
[10:56] <Laurenceb> hmm
[10:56] <Laurenceb> I want something with a top hat frequency response
[10:57] <shellevil> you can approximate that with several in series, appropriately tuned
[10:58] <shellevil> just an option - they already exist and are cheap. Though not very small.
[10:59] <Laurenceb> yeah
[10:59] <Laurenceb> hmm the ADL5387 datasheet recommends a 64Hz high pass on the IF
[10:59] <Laurenceb> so your knocking out ~128Hz
[11:01] <Laurenceb> but their input power is >-70dBm
[11:01] <Laurenceb> and mine is ~-100, so I'm not sure how well it will work
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[11:08] <shellevil> On reflection, it's been a while since I looked, and they seem unavailable.
[11:08] <shellevil> (IF cans)
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[11:42] <Laurenceb> I've just taken a look at my corona receiver and it has a couple
[11:42] <Laurenceb> and its supposedly direct conversion
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[12:04] <Laurenceb> cya
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[15:24] <hallam> Hi natrium
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[16:46] <rjharrison> ping jcoxon
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[20:06] <jcoxon> evening all
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[20:14] <jcoxon> ping rjharrison
[20:14] <rjharrison> pong
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[20:42] <stilldavid> .jcoxon on the pegasus VI wiki page, you mention hooking up the ntx-2 to the audio out on the gumstix - what kind of software were you running on the gmstx?
[20:42] <jcoxon> stilldavid, originally soundmodem
[20:43] <jcoxon> but then some custom code written by g8khw
[20:43] <stilldavid> ah, cool. and it worked out well? I'm thinking of using a similar setup
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[20:43] <jcoxon> yeah it worked well
[20:43] <jcoxon> i messed it up a little
[20:44] <jcoxon> so the rtty didn't work great but the sstv did
[20:44] <jcoxon> but i reckon the rtty version would work well as wekk
[20:44] <stilldavid> how so wrt the rtty? I'm not planning on any video
[20:44] <jcoxon> well*
[20:44] <jcoxon> oh i put hte shift to close together
[20:44] <stilldavid> and did you just run fldigi on the ground?
[20:44] <jcoxon> so it didn't decode very well
[20:44] <jcoxon> yeah
[20:45] <stilldavid> I'm going to try to get a US version (144.39) version of the hx1
[20:46] <stilldavid> might be wanting to pick your brain later :)
[20:46] <jcoxon> np
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[20:55] <stilldavid> also wondering, the FAA over here across the pond requires a remotely operated cut-down device...
[20:56] <jcoxon> yes
[20:56] <jcoxon> they require 2
[20:56] <stilldavid> meaning 2-way communication
[20:56] <jcoxon> no they want 2 methods
[20:56] <jcoxon> one is the bursting of the balloon
[20:57] <stilldavid> but the one has to have ability for remote control, yes?
[20:57] <jcoxon> the other is a cutdown such as a nichrome wire or such
[20:57] <jcoxon> i don't think it has to be remote controlled
[20:58] <stilldavid> right you are, doesn't mention it. alright, that's it for now then
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[21:13] <jcoxon> hey SpeedEvil
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[21:13] <Laurenceb> hello
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[21:13] <shellevil> hey
[21:13] <shellevil> not tried assembly yet - been wrestling with plumbing.
[21:14] <jcoxon> np
[21:14] <shellevil> I found out why my baths have been cooler than usual, and the hot water diddn't last as long as it should.
[21:14] <shellevil> The hot water has been pissing down the back of the tap 24/7
[21:14] <shellevil> Unsure how long for.
[21:15] <shellevil> And can I find the tap spanner? Meh.
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[21:16] <Laurenceb> :P
[21:17] <Laurenceb> theres a flaw in my scanner concept - the vector demod is fed LO at twice the RF frequency
[21:18] <Laurenceb> with is then converted to two phase shifted versions internally - problem is that introduces very strong harmonics
[21:18] <Laurenceb> so its going to be sensitive to RF at multiples of the center freq selected
[21:18] <shellevil> yeah - I was going to say that when you came back
[21:18] <Laurenceb> - not a problem for most applications where you can stick a SAW filter on the front
[21:18] <shellevil> depedns on the shaping I guess
[21:19] <shellevil> but still - it's unlikely to be a nice pure sine
[21:19] <Laurenceb> I think the design is going to have to be changed
[21:19] <Laurenceb> I'm thinking first convert to a high IF
[21:19] <shellevil> 10.7M or somethign?
[21:20] <Laurenceb> more like 3GHz
[21:20] <shellevil> higher inherent noise
[21:21] <Laurenceb> well it means you can stick in another gain stage
[21:21] <shellevil> there are nice SAW filters in the few hundred meg - few hundred gig range
[21:21] <Laurenceb> yeah
[21:21] <shellevil> for GSM bandpass, forex.
[21:21] <Laurenceb> RF -> LNA -> mixer -> LC -> SAW -> gain -> vector demod
[21:22] <shellevil> LC->saw
[21:22] <shellevil> ?
[21:22] <Laurenceb> yes
[21:22] <Laurenceb> SAW filters arent perfect
[21:22] <shellevil> oh - way out of band
[21:22] <Laurenceb> yep
[21:22] <Laurenceb> the tricky thing is choice of IF
[21:23] <Laurenceb> I was thinking you could run with IF~1GHz for DC to 2.5GHz RF
[21:23] <Laurenceb> but that doesnt work - due to LO harmonics
[21:24] <Laurenceb> I think you actually need 5GHz ie RF_max*2
[21:24] <shellevil> umm
[21:25] <shellevil> Is it impossible to keep the LO sinusoidal enough?
[21:25] <shellevil> oh - you've got mixer nonlinearity
[21:25] <Laurenceb> yeah
[21:26] <Laurenceb> FR4 transmission lines will work ok up to 5GHz approx?
[21:27] <shellevil> never done
[21:28] <Laurenceb> I seem to remember that from somewhere
[21:28] <Laurenceb> http://www.analog.com/en/rfif-components/mixersmultipliers/adl5350/products/product.html
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[21:40] <Laurenceb> http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1011,C1725,P36240#descriptionSection
[21:40] <Laurenceb> that would get to ~1.3GHz input frequency
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[22:06] <Laurenceb> I've just realised - if you follow this approach you dont need seperate I and Q channels
[22:23] <SpeedEvil> I don't see why you were wanting them in the first place
[22:23] <SpeedEvil> oh - you were going homo
[22:23] <SpeedEvil> dyne
[22:24] <SpeedEvil> zero IF, for which you do
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[23:41] <jcoxon> oooo some helli on 40m
[23:41] <jcoxon> so cool
[23:42] <shellevil> helli?
[23:43] <shellevil> Alas tonight I've been repairing bath and shovels, tomorrow should have thingy setup hopefully.
[23:44] <jcoxon> hellschriber
[23:45] <jcoxon> where the write the letters in the waterfall
[23:45] <jcoxon> they*
[23:46] <shellevil> ah
[23:47] <shellevil> Silly mode is silly.
[23:47] <shellevil> Is there a less spectrally efficient mode?
[23:47] <jcoxon> hehe
[23:47] <jcoxon> it suprises people though how successful it is
[23:47] <jcoxon> also picked up a PSK station in the US
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[00:00] --- Thu Apr 16 2009