highaltitude.log.20150601

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[09:13] <simium> Morning, gentlemen. I just saw this in r/space and thought that it would be of great interest for you: https://www.youtube.com/watch?v=tI6alFMD79I
[09:13] <simium> A couple of guys tracked their HAB with a telescope until it popped.
[09:14] <simium> Awesome? Awesome.
[09:15] <eroomde> that has been done here a few times, on the rare british days where there;s not too much wind or cloud cover
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[09:18] <michemto> Awesome it is!
[09:18] <michemto> Guys, how many of you have sent cameras up with 100g Hwoyee
[09:19] <simium> Nice, eroomde! In my case it's the first time I've seen it
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[09:23] <eroomde> michemto: i believe a number have, although 100g balloons rarely get to altitudes sufficient for really interesting pictures
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[09:24] <michemto> just thinking about cheap price and opportunities...
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[09:25] <eroomde> well you certainly can
[09:25] <eroomde> nothing stopping you
[09:32] <mattbrejza> a 300g balloon can get >30km and still only needs a small cylinder (1.8m3)
[09:34] Nick change: fl_0|afk -> fl_0
[09:38] <RealBorg> I didn't expect visual tracking to be possible
[09:38] <RealBorg> to much wind / movement at certain altitudes
[09:38] <eroomde> it is a function of wind certainly
[09:39] <eroomde> but if the wind is low it's easy
[09:39] <eroomde> you can see a hab quite easily from about 50km away if it's up at 30km
[09:39] <eroomde> it looks like a small daytime star
[09:40] <RealBorg> I'd only try with radar tracking
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[09:41] <eroomde> you'd probably want a nice radar reflector to give it an appreciable signature
[09:41] <eroomde> or use secondary radar
[09:42] <michal_f> speaking of radal reflectors - is it worth the effort security wise ?
[09:45] <nickjohnson> Has anyone done much with receiving broadcast time signals?
[09:46] <nickjohnson> I'd like to use the 60KHz signal in the UK to control a VCTCXO
[09:46] <nickjohnson> I think all I need is a simple tuned circuit and amplifier to get the 60KHz carrier
[09:47] <eroomde> that is definitely all you need
[09:47] <eroomde> it's basically the classic crystal radio
[09:47] <eroomde> well no it isn't as it's not AM
[09:48] <nickjohnson> Any pointers to a concrete circuit that uses modern components?
[09:48] <eroomde> but it's not complicated - you could probably just sample it directly with an 8bit micro's ADC
[09:48] <nickjohnson> Well, actually, that's the complication - they OOK it to encode time data, so it needs to keep working okay when the carrier's off the air
[09:48] <nickjohnson> My tentative plan was to get the 60KHz and feed it into a PLL with the TCXO as the local oscillator
[09:49] <nickjohnson> And use a comparator to get a square wave rather than sampling it in analog
[09:50] <eroomde> if you have a vctcxo you could then close the loop on the tcxo
[09:50] <eroomde> so basically get some kind of pulse-per-500ms from the 60khz time signal
[09:51] <eroomde> and count the number of oscillations from the tcxo in that time
[09:51] <nickjohnson> That's what I was thinking. Well, not the pulse-per-500ms thing
[09:51] <eroomde> then with a very, very narrow bandwidth on the feedback, use the micro to change the voltage control value to get the tcxo up to the right frequency
[09:51] <nickjohnson> I was thinking I'd divide the 60khz by 3, and the 10MHz by 500, and use a phase comparator to drive the voltage adjust on the VCTCXO
[09:51] <eroomde> that's basically how gps disciplined oscillators often work
[09:52] <eroomde> they use the GPS's pulse-per-second to count the OCXO oscillations
[09:52] <eroomde> and over hours/days/weeks adjust the ocxo
[09:52] <nickjohnson> Yeah, that might be more straightforward, and would remove the issue of what to do when the carrier turns off every second
[09:52] <eroomde> yes
[09:52] <eroomde> exactly
[09:52] <eroomde> and if you loose 60khz just implement logic in the micro to let the tcxo freewheel
[09:53] <nickjohnson> You could actually just count TCXO edges during n edges of the carrier while it's on, no need for a 500ms pulse
[09:53] <nickjohnson> Eg, discard the count if it goes over some value
[09:53] <eroomde> the only thing is that the pps (or pp500ms) edge will be slightly jittery from pulse to pulse, so you must keep the feedback bandwidth very low
[09:53] <eroomde> so that over hundreds of ppses it averages out
[09:53] <nickjohnson> right
[09:53] <eroomde> but that's basically normal and what GPSDOs use
[09:53] <eroomde> so yes
[09:54] <eroomde> you could make a $5 high precision frequency standard :)
[09:54] <nickjohnson> That was my thought
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[09:54] <nickjohnson> Although it'll have an annoying antenna :P
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[09:54] <eroomde> yeah
[09:54] <eroomde> some kind of coil
[09:54] <nickjohnson> So, where do I look for a tuned circuit that will let me output a nice clean 60khz square wave?
[09:55] <nickjohnson> All the existing MSF receivers have envelope followers, so they output demodulated data
[09:55] <nickjohnson> Which is useless to me
[09:56] <nickjohnson> Hm, perhaps I should put a bulkhead BNC jack on my instrument so I don't need to waste a card slot on the oscillator
[09:57] <nickjohnson> Since I'll need an external antenna anyway, may as well make the whole thing external
[09:57] <eroomde> i think the crytal radio circuit is a good starting point though
[09:57] <eroomde> so just a tuned bit
[09:57] <eroomde> then an amplification stage
[09:57] <eroomde> then maybe a saturated transistor stage to act as a very simple comparator
[09:58] <nickjohnson> Why not an actual comparator?
[09:58] <nickjohnson> So, I really don't want any circuit that includes a local oscillator, do I?
[09:58] <eroomde> i'm playing parts golf
[09:58] <eroomde> no you don't but you don't need one
[09:58] <nickjohnson> Most of them are superhet, which seems like it won't work
[09:58] <nickjohnson> For instance: http://www.creative-science.org.uk/MSF4.html
[09:59] <eroomde> the only thing is that this is not immune from nosie especially
[09:59] <eroomde> so you probably want some kind of pll to lock on
[09:59] <eroomde> you could do that on the microcontroller quite easily
[09:59] <pc1pcl> tuned 'bits' : http://www.creative-science.org.uk/MSF3.html ; probably can get them ready made, like the ones used for DCF77 units.
[10:00] <nickjohnson> pc1pcl: Was just reading that very page
[10:00] <nickjohnson> eroomde: Doing a digital version of the procedure I described above, you mean?
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[10:01] <nickjohnson> If I have a PLL, do I even need the counter?
[10:01] <eroomde> i don't remember reading about a counter
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[10:02] <simium> If I were to fly some kind of gopro, what's better? Housing or not housing? I'm worried about condensation on the plastic housing
[10:03] <nickjohnson> Oh, this looks promising: http://www.creative-science.org.uk/MSF_crystal_filter.html
[10:03] <daveake> no housing
[10:03] <nickjohnson> eroomde: You were talking about counting 10MHz clock edges based on a pps signal from the receiver
[10:03] <eroomde> sure
[10:03] <eroomde> but basically pps from a gps receivewr doesn't have random pulses
[10:03] <eroomde> i suspect your circuit might
[10:04] <eroomde> because it'd be fairly susceptible to noise
[10:04] <eroomde> so you might want some kind of phase-locked loop somewhere to get a 'clean' ppx
[10:04] <eroomde> (x = whatever)
[10:04] <eroomde> and then use the square-wave output of that to trigger against
[10:04] <nickjohnson> ah
[10:05] <nickjohnson> Instead of a PLL just to lock on to the 60KHz, though, wouldn't it make sense to use the 10MHz oscillator as the VCO in the PLL?
[10:05] <nickjohnson> Then you don't need a second stage
[10:07] <eroomde> yes - they're broadly equivalent
[10:08] <eroomde> the counting bit just happens when you divide the tcxo back down to go into the phase detector with the 60khz
[10:08] <nickjohnson> true
[10:08] <nickjohnson> That was my original idea, at least, but it relies on making the PLL behave nicely when the carrier goes away
[10:08] <eroomde> yes
[10:09] <eroomde> i'd probably just use a micro still so you can adaptively tune the circuit
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[10:10] <nickjohnson> Fair enough
[10:11] <nickjohnson> So, antenna, tuned circuit, amplifier, 4046 PLL, micro?
[10:12] <eroomde> worth a stab
[10:12] <nickjohnson> Though it looks like the 4046's phase comparators will tend to drift towards the center or extremes with no input signal
[10:13] <eroomde> you could just sanity-check the PPL output in the micro
[10:13] <nickjohnson> Well, I can easily have an envelope follower circuit that tells me if the carrier is present at the time
[10:14] <nickjohnson> Or, wait, I think the 4046 has a lock output pin
[10:14] <eroomde> a goertzel filter or something on the micro, perhaps
[10:14] <eroomde> just to see if 60khz is there
[10:14] <nickjohnson> Wrong, it doesn't
[10:14] <nickjohnson> Well, the PLL will always output something, but without the input signal it'll drift away from lock
[10:16] <eroomde> sure
[10:16] <nickjohnson> I have a friend who GPS-disciplined his rubidium oscillator for use as an NTP source
[10:16] <nickjohnson> I should hit him up for advice
[10:16] <eroomde> so the gortzel filter can hopefully tell you this
[10:16] <nickjohnson> Can't I just count edges directly to figure out if it's in range?
[10:16] <nickjohnson> Oh, you're talking about amplitude
[10:16] <nickjohnson> In that case, can't I just envelope-follow the output of the amp?
[10:16] <eroomde> no i'm talking about the power at 60khz really
[10:17] <eroomde> but if it's square you could edge-count
[10:17] <eroomde> 59900 < count < 60100 or whatever
[10:18] <nickjohnson> hmm
[10:18] <nickjohnson> It seems to be getting more complicated :P
[10:18] <pc1pcl> Is the MSF 60khz signal completely 'off' during the 'off' keying, or like DCF77, just reduced in amplitude?
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[10:20] <nickjohnson> Oh, this appnote has a PLL lock detector circuit: http://www.ti.com/lit/an/scha002a/scha002a.pdf
[10:20] <nickjohnson> pc1pcl: Completely off as far as I know
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[10:21] <nickjohnson> Yup, completely off
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[10:34] <nickjohnson> GPSDO certainly seems simpler at this point :P
[10:34] <nickjohnson> Having to get a GPS lock is the issue
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[10:39] <SpeedEvil> why?
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[10:39] <SpeedEvil> what ar eyou trying to do - apoloigiews - I haven't read back far enough to hit the beginning og the conversation
[10:39] <nickjohnson> Because receivers output a reliable 1PPS, and all you have to do is count oscillator edges per pulse
[10:40] <nickjohnson> SpeedEvil: Create a disciplined oscillator from a VCTCXO and the MSF 60khz time signal
[10:40] <SpeedEvil> I mean - why not GPS?
[10:41] <SpeedEvil> Laurenceb__: did a ridiculously accurate GPSDO - I don't know if he's published it, or intends to, or if it's suitable.
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[10:41] <nickjohnson> SpeedEvil: Oh. Because receiving GPS indoors is impossible, and getting an antenna outdoors is awkward
[10:41] <Upu> http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=107&products_id=234
[10:41] <SpeedEvil> ah
[10:41] <nickjohnson> The attraction here was being able to build a black box that Just Works
[10:41] Nick change: fl_0 -> fl_0|afk
[10:42] <SpeedEvil> nickjohnson: What sort of accuracy are you looking for?
[10:42] <eroomde> i'm not sure what a ridiculously accurate GPSDO is
[10:42] <eroomde> it's quite hard to make bad ones
[10:42] <nickjohnson> SpeedEvil: Significantly better than the TCXO alone
[10:42] <eroomde> and it's quite easy to get them about as good as gps clocks allow
[10:42] <eroomde> this isn't a hard exercise
[10:42] <SpeedEvil> eroomde: I forget the details.
[10:42] <nickjohnson> Upu: Hm, not bad, though using a PLL will introduce jitter that a 10MHz TCXO output alone wouldn't have
[10:43] <nickjohnson> eroomde: The GPS one seems easy, given a 1PPS output. The MSF version seems trickier.
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[10:43] <SpeedEvil> In principle, you could just digitise it at ~180KHz on the micro, after a nice filter
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[10:44] <SpeedEvil> And then do the phase accumulation in software
[10:44] <gonzo___> the old jupiter12 GPS rx was nice, had a 10KHz output
[10:44] <SpeedEvil> run the micro clock of the disciplined oscillator
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[10:44] <craag> the ubloxes have a programmable output
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[10:45] <gonzo___> interesting, what is the upper freq for them?
[10:45] <craag> although as they use a pll you get some jitter at most freqs
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[10:45] <craag> 10MHz iirc
[10:46] <SpeedEvil> I think Laurenceb__ found some reclocker chip that went from 1Hz+VTCXO to a nice clean output
[10:46] <gonzo___> really, then the G4JNT simple gpsdo cct could be used with that still
[10:46] <nickjohnson> SpeedEvil: The problem, as eroomde pointed out, is that the received signal will be noisy, so a PLL on the input would be an asset
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[10:46] <gonzo___> I use a ZAZ design at the mo. FLL on the 1pps
[10:47] <nickjohnson> SpeedEvil: You just need a VCTCXO and a microcontroller with a DAC for that
[10:47] <SpeedEvil> nickjohnson: yes - you don't rely on the ADC at all
[10:47] <SpeedEvil> nickjohnson: err - not noisy at all
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[10:47] <nickjohnson> SpeedEvil: Why not?
[10:47] <gonzo___> OCXO is better
[10:47] <nickjohnson> gonzo___: I'm not sure it makes such a big difference by the time you're disciplining your oscillator to a good reference
[10:48] <SpeedEvil> nickjohnson: you simply sample all of the input signal, accept the noise, and do the filtering internally. Simply accumulating I and Q over 60000 cycles will give you a large signal.
[10:48] <eroomde> it still does on phase noise
[10:48] <eroomde> (make a big difference)
[10:48] <nickjohnson> eroomde: hm, okay
[10:48] <gonzo___> you can use a really long time const and not worry about short term temp affecting it
[10:48] <nickjohnson> eroomde: I thought an OCXO just had less drift over temperature than a TCXO?
[10:48] <SpeedEvil> (assuming you'r input crystal is within 1/60000th)
[10:48] <eroomde> like if you're using your 10MHz ref to multiply up to 10GHz
[10:49] <nickjohnson> SpeedEvil: Can't accumulate over 60k cycles, the signal cuts out every second :)
[10:49] <gonzo___> OCXO should be pretty temp insensiitoive
[10:50] <nickjohnson> But yeah, that might be the simplest solution, doing it all digitally after the BPF and amp
[10:50] <nickjohnson> I don't know nearly enough DSP stuff to do it right now, though
[10:51] Nick change: baird_ -> baird
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[10:56] <SpeedEvil> nickjohnson: yes - 60K cycles is one second, which is the on/off period from memory. you accumulate over the whole period - including when the signal is missing.
[10:58] <SpeedEvil> As a very simple explanation, if you are sampling at 240KHz, you add the first signal to your 'I' register, the second to the 'Q', subtract the third from 'I' and then subtract the fourth from 'Q' - then you form a vector from I and Q and work out the magnitude and direction of the vector. This gives you the current phase and amplitude of the signal.
[10:59] <SpeedEvil> If your sampling is not at exactly 240khz, then the received signal for subsequent bits walks clockwise or anticlockwise slowly
[11:00] <eroomde> i tried to explain that bit with diagrams in my gps talk at the conf
[11:00] <SpeedEvil> I'm probably not explaining well, I have sort-of-a-migraine.
[11:00] <eroomde> diagrams are necessary for explaining this
[11:00] <eroomde> for me anyway
[11:01] <SpeedEvil> It can be bad if you've internalised the diagrams, and are eplaining with reference to them internally not realising you're doing it.
[11:01] <eroomde> nickjohnson: my talk is online, it was about hope to decode gps signals but the first half was a general dsp intro
[11:01] <SpeedEvil> ^the above is a good plan
[11:01] <SpeedEvil> Much 'DSP' is really really simple in concept
[11:04] <SpeedEvil> 'how would I do this with a paper and pencil and 74 years'
[11:06] <day> i dont get how the checksum for the ublox commands/messages is calculated. My routine works for the long hex chain that is necessary to switch on the airborne mode. But it does not work for lets say "$PUBX,40,GLL,0,0,0,0*5C" which disables the GLL string
[11:14] <Vaizki> long hex string? are you mixing up UBX and NMEA commands?
[11:14] <SpeedEvil> https://ukhas.org.uk/general:ukhasconference2013
[11:14] <SpeedEvil> eroomde's GPS talks
[11:15] <SpeedEvil> - scroll to recordings
[11:16] <Vaizki> day, to do the NMEA checksum, you take everything between $ and * and XOR them together
[11:16] <day> Vaizki: i might. so i assume checksums are done differently for UBX? I assumed the *5C is one
[11:16] <Vaizki> character by character
[11:17] <day> Vaizki: eh? my checksum for nmea works. but im not xoring anything :/ im using the ck_a = ck_a + buffer[i]; ck_b = ck_a + ck_b
[11:17] <Vaizki> yes, 5C is the checksum, it's hex for the bits 0101 1100
[11:17] <Vaizki> day, that's the UBX checksum
[11:17] <Vaizki> which is 2 bytes
[11:18] <day> great then im completely lost :D
[11:18] <day> because then it should work for above PUBX command
[11:18] <Vaizki> the NMEA checksum is one byte, 8 bits.. it's formed by XORin every character together
[11:18] <Vaizki> UBX is a completely separate fully binary protocol
[11:19] <Vaizki> PUBX is a NMEA command so should have a NMEA checksum I think?
[11:20] <day> hmm if it looks similar its likely to use the same i guess
[11:20] <day> so just byte1 xor byte2 xor byte3 xor ?
[11:20] <Vaizki> ck = 0; for (i=0;i<strlen(nmea_s);i++) ck = ck ^ nmea_s[i]
[11:20] <Vaizki> something like that
[11:20] <Vaizki> yea you can initialize with 0 because then the first XOR will just set the checksum to the first byte
[11:21] <day> k
[11:21] <Vaizki> but don't calculate in the $ or *
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[11:35] <day> Vaizki: hm that was simple >.>
[11:46] <day> thanks a lot
[11:58] <Vaizki> np :)
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[14:13] <SpeedEvil> https://m.youtube.com/watch?v=ymZEOihlIdU real-time mapping of ionospheric structure. Aka why single frequency GPS is hard.
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[16:09] Nick change: Crashbone -> Crashbone|Away
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[16:19] <Lunar_Lander> hello
[16:19] <daveake> hello LL
[16:20] <daveake> Flying this year? :)
[16:20] <Lunar_Lander> hello dave
[16:20] <Lunar_Lander> yeah :)
[16:20] <Lunar_Lander> working on it
[16:20] <daveake> don't rush :)
[16:20] <Lunar_Lander> also tomorrow we got some students who are on the german cansat competition this year
[16:20] <Lunar_Lander> they'll learn soldering and breadboarding
[16:21] <Lunar_Lander> :)
[16:22] <eroomde> make sure the connected the grounds of each of the devices up
[16:22] <eroomde> sure they*
[16:23] <Lunar_Lander> I will
[16:24] <eroomde> pro tip for them
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[16:37] <Lunar_Lander> yea
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[17:38] <SpeedEvil> j
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[18:22] <arko> https://www.youtube.com/watch?v=eJO-gTlhD2U
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[18:35] <michal_f> arko: 'this video is private'
[18:35] <arko> hmm
[18:35] <arko> wonder if its because you may be out of the US
[18:36] <michal_f> it's possible
[18:36] <mattbrejza> it worked first click now its 'private' too
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[20:55] <Laurenceb> http://i.imgur.com/UAxKiT4.png
[20:55] <Laurenceb> logscale spectrograms with gnuplot
[20:56] <Reb-SM3ULC> :)
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[20:58] <chrisstubbs> daveake, good new posts on the PITS site
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[21:14] <day> why does the ukhas.org ublox example code use wrong PUBX commands formats? the datasheet says $PUBX,40,GLL,1,0,0,0,0,0*5D while the guide says $PUBX,40,GLL,0,0,0,0*5C. They both work for some reason, which i find quite odd :/
[21:14] <day> im taking about the length, not how the bits are set
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[21:16] <Ian_> Datasheet v experience. Have you asked if the datasheet is correct perhaps?
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[21:16] <Ian_> :)
[21:17] <day> Ian_: is that a joke?
[21:17] <Ian_> Yes, but have you never detected an error in a datsheet?
[21:18] <day> nothing big
[21:18] <daveake> At a guess, the ukhas ones were taken from Ucenter
[21:18] <Ian_> I rest my case!
[21:19] <daveake> I'd also guess that earlier ubloxii used the shorter command
[21:19] <daveake> and that later chips accept old and new versions
[21:19] <day> makes sense
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[21:23] <eroomde> https://twitter.com/Pinboard/status/605484490291445760
[21:24] <jonsowman> that's a serious beard
[21:27] Nick change: fl_0 -> fl_0|afk
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[21:29] <Reb-SM3ULC> Any HAB with a ADS-B recorder on board? I thought I've seen one but not sure.
[21:35] <SA6BSS> hack5 sent one up in a quadracopter
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[22:16] <_charlie> hi
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[00:00] --- Tue Jun 2 2015