[01:53] <Laurenceb> natrium42: you about?
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[18:02] <Laurenceb> any launch news?
[18:10] <Laurenceb> QFH antennas look good for balloons - http://jcoppens.com/ant/qfh/sim.en.php
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[18:32] <Laurenceb> hello
[18:33] <Laurenceb> do you have any antenna experience?
[18:43] <Simon-MPFH> Moi? Nope - sorry
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[19:07] <Laurenceb> I'm thinking QFH antennas look good for balloons - http://jcoppens.com/ant/qfh/sim.en.php
[19:09] <Simon-MPFH> Pretty pictures!
[19:16] <Laurenceb> yessss
[19:16] <Laurenceb> half way through my horrible problem set
[19:16] <Laurenceb> time for a break bbl
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[19:53] <Laurenceb> hey rocketboyV1
[19:53] <Laurenceb> how was the launch?
[19:54] <Laurenceb> rocketboyV1: I got the tx working, my sound card needed to be calibrated, the sample rate was 2.5% off
[19:56] <Laurenceb> I've gtg, speak 2 u later
[20:02] <rocketboyV1> ok cu later
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[20:14] <Laurenceb> edmoore: how was the launch?
[20:14] <edmoore> beautiful
[20:14] <edmoore> the search, less so
[20:14] <Laurenceb> :P
[20:14] <Laurenceb> oh
[20:14] <Laurenceb> what happened?
[20:14] <edmoore> we had visual with binoculars all the way to the top
[20:15] <Laurenceb> wow
[20:15] <Laurenceb> what altitude?
[20:15] <edmoore> it was only about 5k over the ground away at the top
[20:15] <edmoore> 23k
[20:15] <Laurenceb> cool
[20:15] <edmoore> but then the radio just died all of a sudden
[20:15] <Laurenceb> nooo
[20:15] <edmoore> might have been chaos at apogee
[20:15] <edmoore> or something
[20:15] <edmoore> never got it back
[20:15] <Laurenceb> :(
[20:16] <Laurenceb> maybe the molex connectors?
[20:17] <Laurenceb> hopefully someone will find it
[20:18] <edmoore> who knows?
[20:18] <edmoore> yes, i hope so
[20:18] <Laurenceb> I'm thinking of quad helix antenna for balloons
[20:19] <Laurenceb> http://jcoppens.com/ant/qfh/sim.en.php
[20:19] <Laurenceb> http://jcoppens.com/ant/qfh/img/sim/0.32/x.png it doesnt need a ground plane, and the radiation pattern is nice
[20:20] <Laurenceb> 40 ohm impedance, so it matches a 50 ohm radio module fairly well
[20:21] <edmoore> cool, looks good
[20:21] <Laurenceb> I'll make one soon as I have time
[20:22] <Laurenceb> do you know if the circuit design modules will do RTTY?
[20:23] <Laurenceb> this is cool: http://jcoppens.com/ant/qfh/calc.en.php
[20:25] <Laurenceb> so did you lose visual on the way down?
[20:25] <edmoore> yes
[20:25] <edmoore> i mean, it dropped below our near-by trees
[20:26] <edmoore> and there'd be no hope of refinding it with the binos. needle in a haystack
[20:26] <Laurenceb> ah so you say it cme down?
[20:26] <edmoore> saw*
[20:26] <edmoore> yes
[20:26] <Laurenceb> but without 2 observers
[20:27] <Laurenceb> it doesnt really help
[20:27] <edmoore> yep we had that discussion!
[20:27] <Laurenceb> hehe
[20:27] <edmoore> it would be great if we did have 2
[20:28] <Laurenceb> I want to kit myself out with some radio gear
[20:29] <Laurenceb> it looks cool fun
[20:30] <Laurenceb> the theoretical range of a 10mw module transmitting 300 buad rtty with a big yagi for reception is around 10000Km !
[20:30] <edmoore> lol
[20:30] <Laurenceb> if you use an LN2 cooled preamp and antenna :P
[20:30] <edmoore> wouldn't it be nice!
[20:30] <Laurenceb> and a dish....
[20:30] <Laurenceb> then you could go much further
[20:30] <Laurenceb> the moon :D
[20:31] <Laurenceb> your limited by thermal noise
[20:32] <Laurenceb> get jodrell bank on the job :P
[20:33] <Laurenceb> pity we cant use shortwave, then insane ranges would be easier
[20:35] <Laurenceb> http://news.bbc.co.uk/1/hi/sci/tech/7217726.stm lol @ 3rd photo
[20:37] <Laurenceb> edmoore: do you know anything about stripline techniques?
[20:37] <edmoore> nope
[20:39] <Laurenceb> I was thinking of designing a stripline QAM system
[20:40] <Laurenceb> maybe BPSK as QAM isnt ideal for low bandwidth with moving antennas
[20:40] <edmoore> sounds like a group of rappers
[20:41] <Laurenceb> :P
[20:41] <edmoore> we were talking about bpsk today
[20:41] <Laurenceb> QAM=quadrature amplitude modulation
[20:41] <edmoore> yes i recall
[20:42] <edmoore> but yes, it seems there are bpsk like systems used by hams
[20:42] <Laurenceb> its possible (I think) to do it with mosfets and striplines
[20:42] <edmoore> that are quite achievable
[20:42] <Laurenceb> use the transmission lines to get the phase delays
[20:43] <Laurenceb> of course we could just use one of the AD DDS chips, but using striplines we could power it with a modules
[20:43] <edmoore> yeah
[20:44] <Laurenceb> still I'm not sure if its still legal... but it doesnt add to the broadcast power
[20:45] <Laurenceb> if I get this studentship at SST i'll be spending many a happy day working with phase modulation systems :P
[20:46] <Laurenceb> this is kind of cool: http://en.wikipedia.org/wiki/Image:PAL_colour_bar_signal_measured_vector_edit.png
[20:46] <Laurenceb> nice way to visualise PAL
[20:46] <edmoore> yeah
[20:52] <Laurenceb> hehe: http://www.radioworld.co.uk/~radio/catalog/20921-tonna-70cm-434mhz-yagi-p-2325.html?osCsid=f2b6ed6b299a41a6f7f15825afd04709
[20:53] <Laurenceb> 4.6m long !
[20:53] <edmoore> that would be ideal for a roof mounted thingamy
[20:54] <Laurenceb> http://www.radioworld.co.uk/~radio/catalog/a430s15-diamond-430440mhz-70cm-yagi-p-3963.html?osCsid=f2b6ed6b299a41a6f7f15825afd04709
[20:54] <Laurenceb> is a little more practical :P not a bad price as well
[20:56] <Laurenceb> did you ever build the servo controlled antenna?
[20:56] <edmoore> degree happened
[20:56] <edmoore> but one day!
[20:56] <Laurenceb> lol
[20:57] <edmoore> really wanted to put a scope on it aswell after seeing how good the binoculars were today
[20:57] <Laurenceb> hmm youd want to keep the servos away from the center
[20:59] <edmoore> wyzat?
[21:01] <Laurenceb> they would interfere with the rf propogation
[21:04] <edmoore> ok
[21:05] <edmoore> I was going to do as we've done to date
[21:05] <edmoore> have them on the CoG, where the CoG is shifted back by a counterweight to the end of the yagi
[21:06] <Laurenceb> sure
[21:13] <Laurenceb> dammit these lecture notes use weird fonts, and I cant display them :(
[21:13] <Laurenceb> not sure if thats a valid excuse for not doing any work....
[21:16] <Laurenceb> hmm wikipedia is quite good :p heres what I'm working on - http://en.wikipedia.org/wiki/Boussinesq_approximation_%28water_waves%29
[21:17] <Laurenceb> lots of lovely fluid dynamics....
[21:21] <Laurenceb> the annoying thing about physics is that its so maths based, I didnt actually get what the equations were describing until I saw that animation on wikipedia
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[21:31] <Laurenceb> omfg http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140204418857
[21:31] <Laurenceb> I got outbid - thats a crazy price
[21:33] <Laurenceb> :(
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[21:51] <Laurenceb> you can buy an icom pcr-1500 for £255 new from the US
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[21:59] <Laurenceb> -125 dBm sensitvity :D
[22:03] <fnoble_> yo' possie
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[22:04] <rocketboyV1> hey edmoore - any news?
[22:05] <edmoore> we went for a bit of a wander around a hill and some fields around where we guessed it might be from the 1200 GFS data
[22:05] <edmoore> no joy
[22:05] <edmoore> I think we would have heard something if there was anything to hear - we had a good vantage point
[22:06] <fnoble_> fits with the power faliure hypothesis
[22:07] <rocketboyV1> humm yes my guess too - just didn't start up agian
[22:07] <fnoble_> the points we managed to piece together from james' laptop fitted quite well with the 1200 prediction
[22:07] <fnoble_> scaled a bit for our higher ascent rate
[22:08] <rocketboyV1> humm - can yo scale the descent too
[22:08] <fnoble_> didnt try scaling it properly, just from looking at them map :)
[22:08] <rocketboyV1> I could work out an approximate rate
[22:09] <rocketboyV1> of descent based on the chute and weight
[22:10] <rocketboyV1> have we got an esitmate of a timed ascent path
[22:10] <rocketboyV1> ?
[22:10] <rocketboyV1> if so I could predict a descent path
[22:11] <Laurenceb> bad luck :(
[22:11] <edmoore> james has the numbers
[22:11] <rocketboyV1> ok - I'll mail him
[22:12] <Laurenceb> rocketboyV1: your path loss calculator, whats the difference between the sky noise and noise figure ?
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[22:13] <rocketboyV1> sky noise is background EM noise from the sun/stars etc.
[22:14] <rocketboyV1> noise figure is a way of specifying the noise generated by the reciver front end
[22:14] <rocketboyV1> So thats thermal noise in the transistors etc.
[22:15] <Laurenceb> ah ok
[22:15] <Laurenceb> so it has an apparent temperature?
[22:16] <Laurenceb> oh bte, do you think thst the circuit design modules will work with rtty?
[22:16] <rocketboyV1> somme revivers just specify a miniumum recive level (e.g. -nnn dBm) for a given S/N output - that much easier to work with
[22:17] <Laurenceb> yes, I have that for an icom, its -125
[22:17] <rocketboyV1> -125dBm for 12db SINAD?
[22:17] <Laurenceb> not sure
[22:17] <Laurenceb> I though it was just the noise floor?
[22:18] <rocketboyV1> I doubt its -125dBm to the noise flllo
[22:19] <rocketboyV1> floor
[22:19] <Laurenceb> too good?
[22:19] <rocketboyV1> yep
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[22:19] <Laurenceb> well, it says sensitivity on the datashee
[22:20] <hrf_jack> hi everybody
[22:20] <Laurenceb> and I worked it out from thst
[22:20] <Laurenceb> hello
[22:20] <hrf_jack> how did the launch go?
[22:20] <Laurenceb> not very well, they lost it ;(
[22:20] <hrf_jack> :(
[22:20] <hrf_jack> lost communication?
[22:20] <edmoore> yep
[22:21] <Laurenceb> so from the sensitivity in uV, I calculated -125 dBm
[22:21] <edmoore> radio died over about 1 second
[22:21] <edmoore> both radios lost it simultaneously
[22:21] <rocketboyV1> so whats it in uV?
[22:21] <Laurenceb> the "sensitivity"
[22:21] <Laurenceb> 0.4
[22:22] <hrf_jack> when did they loose it, asc or desc?
[22:22] <rocketboyV1> Ah OK - not too bad - The Ft790 is 0.16uV
[22:22] <Laurenceb> cool
[22:22] <Laurenceb> I plan to buy one
[22:22] <Laurenceb> the department has one, but one just went on ebay for £220
[22:23] <Laurenceb> when you can buy the latest one new for £290
[22:23] <Laurenceb> or £250 from the US
[22:24] <Laurenceb> so, if the noise is -125 dbm, now do i use that in the spreadsheet?
[22:25] <rocketboyV1> thats 3.2 x 10 to neg 12 mW
[22:25] <Laurenceb> hang on.... does that give noise Temperature?
[22:26] <rocketboyV1> nope
[22:26] <Laurenceb> what I'm saying is can I convert into apparent temperature?
[22:27] <Laurenceb> from a -125 dBm noise figure
[22:28] <rocketboyV1> 1 x 10 neg 12 is -120dBm
[22:29] <Laurenceb> yes
[22:29] <rocketboyV1> 10 x 10 neg 12 is -110dBm
[22:29] <Laurenceb> hmm dont I require the noise power spectral density
[22:29] <Laurenceb> ?
[22:29] <rocketboyV1> so 3.2 x 10 neg 12 is 115dBm
[22:30] <Laurenceb> what are you getting at?
[22:30] <rocketboyV1> well for one your calculation is wrong - the sensitivity is -115dBm
[22:31] <rocketboyV1> me thinks
[22:32] <Laurenceb> ah yes ok I see
[22:33] <rocketboyV1> 0.4 uV is 0.4 x 10 neg 6 Volts
[22:33] <rocketboyV1> so the power into 50 ohms is that squared / 50
[22:33] <Laurenceb> yep v^2/R
[22:33] <Laurenceb> http://en.wikipedia.org/wiki/Noise_temperature
[22:33] <Laurenceb> dont I need the spectral density?
[22:34] <Laurenceb> of the noise to find an effective temperature
[22:34] <Laurenceb> so is that noise over some bandwidth?
[22:34] <rocketboyV1> what like a spectral density function
[22:34] <rocketboyV1> ?
[22:34] <Laurenceb> yes
[22:34] <Laurenceb> or some approximation as we have small bandwidth?
[22:35] <rocketboyV1> just assume its flat over the passband of the 3dB points of the reciver
[22:35] <Laurenceb> right
[22:35] <Laurenceb> so how do we use that approximation to find the effective temperature?
[22:36] <Laurenceb> "N is the noise power spectral density (W/Hz)" so divide by 3*10^3 ?
[22:36] <Laurenceb> ie 3 kHz bandwidth
[22:37] <rocketboyV1> I'm not sure why you would if yo have the recieve sensitivity
[22:37] <Laurenceb> we have to know the bandwidth?
[22:38] <rocketboyV1> yep
[22:38] <Laurenceb> isnt sensitivity saying what the noise is?
[22:38] <Laurenceb> so to work out temperature from the noise we need to know the spectral density, ie we need the bandwidth
[22:39] <rocketboyV1> is the recive level for a certain S/N out (at the speaker)
[22:39] <Laurenceb> as we assume its smooth, so the noise power spectral density (W/Hz)
[22:39] <Laurenceb> ok
[22:39] <Laurenceb> so say its for S/N=1 (need to check the datasheet, but for the sake of argument)
[22:40] <Laurenceb> then noise power spectral density = 10^-3*10^-11.5/bandwidth ?
[22:41] <rocketboyV1> so just assume the noise is spread over the audio spectrum (2.4Khz) and the signal is a single frequency
[22:41] <Laurenceb> ah then our FFT can filter out the noise
[22:41] <rocketboyV1> so then if you apply a fiter that takes in the signal and some part of the noise
[22:42] <Laurenceb> so we need the datarate - 300 baud
[22:42] <rocketboyV1> thats what TrueTTY does
[22:42] <Laurenceb> cool
[22:42] <Laurenceb> or fldigi :D
[22:42] <Laurenceb> ah I understand now :P
[22:42] <rocketboyV1> so you umprove the S/N by taking in less of the noise
[22:42] <Laurenceb> sure
[22:42] <Laurenceb> right got it :D
[22:43] <Laurenceb> thanx
[22:43] <rocketboyV1> if you have the sensitivity you don't need to know about noise figures
[22:43] <Laurenceb> btw, fldigi was giving me problems as the sound card had a sample rate error of 2.5%
[22:43] <Laurenceb> its working nicely now
[22:45] <Laurenceb> ok, I'll have to think about this one
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[22:45] <Laurenceb> as the reciever noise will be spread actoss audio frequency, and we have only a small bit of audio frequency
[22:46] <Laurenceb> about 10% can interfere with our decoding
[22:46] <rocketboyV1> yep - there are a couple of issues
[22:46] <rocketboyV1> the spec is signal to signal plus noise
[22:46] <Laurenceb> so that takes us to -125 dBm
[22:47] <rocketboyV1> what does?
[22:47] <Laurenceb> truetty
[22:47] <Laurenceb> as it filteres out 90% of the noise - reciever bandwidth is ~ 3Khz
[22:47] <Laurenceb> signal bandwidth ~300
[22:48] <rocketboyV1> yeah for 300Hz you would get a 10dB improvement
[22:48] <Laurenceb> cool
[22:48] <Laurenceb> bbl
[22:48] <rocketboyV1> cu
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[23:20] <Laurenceb> back
[23:21] <Laurenceb> so... with Tsky=100K the noise over the 300hertz bandwidth is -148 dBm
[23:23] <Laurenceb> so thats well under the icom scanner noise (-125)
[23:23] <Laurenceb> so the range is around 4000Km with a large yagi (15 dBi)
[23:24] <Laurenceb> and a quad helix on the balloon
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[23:40] <natrium42> Laurenceb, that doesn't account for earth curvature
[23:40] <natrium42> you won't get LOS
[23:44] <Laurenceb> sure
[23:44] <Laurenceb> I'm thinking why bother with expensive scanners when you could make your own....
[23:44] <Laurenceb> http://www.nxp.com/acrobat_download/datasheets/SA612A.pdf
[23:45] Action: natrium42 still says to use satellite
[23:45] <Laurenceb> hehe
[23:45] <Laurenceb> with a few ics it should be possible
[23:47] <natrium42> how would you test the performance and tune it?
[23:47] <natrium42> it looks like black magic to me
[23:47] <Laurenceb> lol
[23:47] <Laurenceb> basically all I need is a LNA, mixer and oscillator
[23:47] <Laurenceb> then use the mixer to downconvert
[23:48] <Laurenceb> then a filter on the output, to bandpass audio frequency
[23:48] <Laurenceb> then oscillator is a bit hard, best to go for gps syncronised :P
[23:50] <natrium42> what about gps synched communication?
[23:50] <Laurenceb> yes, that would be cool
[23:50] <Laurenceb> actually SSB is harder... I'm not sure how to do that
[23:50] <natrium42> say you transfer at 15:35:45 UTC
[23:50] <natrium42> 45 would be one piece of information
[23:51] <natrium42> 15:36:32 UTC
[23:51] <natrium42> 32 would be nect piece of information
[23:51] <natrium42> etc
[23:51] <natrium42> so you would only need high power pulses
[23:52] <natrium42> and when you receive them is the information :P
[23:52] <Laurenceb> sure
[23:52] <natrium42> has that scheme been ever used?
[23:53] <natrium42> i guess there are many disadvantages like lack of error correction
[23:54] <Laurenceb> not to my knowledge
[23:54] <natrium42> bbl food
[23:59] <Laurenceb> http://lea.hamradio.si/~s53mv/zifssb/block.html
[00:00] --- Mon Feb 11 2008