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<solrize>
are there still any ben nanonotes around?
<FrankBlues>
I have one... kinda gathering dust atm
<solrize>
neat
<FrankBlues>
I've been thinking about running emulators on it - I used to have VICE working, and I thought someone had one of the older Mac emulators working
<solrize>
nice! i didn't know about vice
<ysionneau>
newbie question but, would it be very hard to make a simple 2.4 GHz GFSK demodulator?
<ysionneau>
I guess that the fact that some part of the circuit would need to handle high frequency (GHz) is what would be the big issue for DIY
<ysionneau>
but if you buy some IC to do the PLL part for instance, maybe it's feasible, right?
<FrankBlues>
There's a Dingux port of VICE that used to run on Ben, last time I tried it had strange dependency issues that I never got around to fixing.
<solrize>
ysionneau, i imagine something like an AM detector to get rid of the baseband, then a hardware or software PLL? but i have no idea how stuff works at those frequencies
<solrize>
bjj
<ysionneau>
I mean, as long as I have a PLL to lock on the 2.4 GHz carrier
<solrize>
oops
<ysionneau>
and then I can demodulate by mixing the input signal with the PLL locked output
<ysionneau>
all of this is the "hard part" because it runs at 2.4 GHz
<ysionneau>
after that, it's baseband indeed
<solrize>
you have a 2.4 ghz pll? that's what i didn't realize was possible, at least in the dinky equipment (e.g. bluetooth) that i imagine you're dealing with
<ysionneau>
how can you demodulate a bluetooth signal without a 2.4 GHz pll ?
<ysionneau>
I thought this was mandatory
<larsc>
sample _all_ the baseband ;)
<ysionneau>
sample with 4.8 GHz ADC?
<ysionneau>
and then do everything as SDR
<ysionneau>
but you need very expensive electronics
<solrize>
" i have no idea how stuff works at those frequencies" => pure speculation but i was imagining some crude LC filter made of pcb trace, then a diode detector
<larsc>
ysionneau: there are lots of SDR platforms which allow you to sample at 2.4GHz with a limited bandwidth
<solrize>
you should probably ask on #electronics where there might be some analog rf folks hanging out
<larsc>
say a few MHz
<solrize>
larsc, is that stuff big and complicated? i was presuming this is for cheap low performance gear like wifi or bluetooth
<ysionneau>
larsc: I am searching for very low price solutions
<larsc>
solrize: depends on your definition of big and complicated
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<larsc>
ysionneau: but you want the digital bt signal?
<wpwrak_>
ysionneau: what do you want to accomplish in the end ? build an SDR system ? receive BT ? something else
<ysionneau>
receive BTLE
<solrize>
larsc, big/complicated = you can't build it into a 5 dollar consumer gizmo
<larsc>
the cheapest solution is probably a off the shelf bt receiver
<ysionneau>
well, in fact I want to learn RF
<ysionneau>
I think I will start with a simple FM demodulator
<larsc>
then it's not going to be cheap ;)
<wpwrak_>
ysionneau: have you been following what i'm doing on anelok ?
<ysionneau>
wpwrak_: yes :)
<wpwrak_>
and do you just want to receive or also send ?
<ysionneau>
pretty cool stuff
<wpwrak_>
then you already know some chips you can use :)
<ysionneau>
yes
<ysionneau>
but I would like to replace the chip with home made circuitery
<ysionneau>
when it's possible
<ysionneau>
to learn the RF part
<wpwrak_>
oh, i see. ah yes, there are components for that, too. and fpgas may come in handy, too
<solrize>
larsc this is the copyleft hardware channel, using off the shelf bt doesn't count ;-). i've been wondering about this myself because of the suspicious code blobs in all the bt processors
<larsc>
solrize: where do you draw the line?
<ysionneau>
larsc: I want to demodulate, then I get the baseband analog signal, then I can sample with cheap ADC and get the digital stream
<ysionneau>
it's just for fun, no big precise goal
<larsc>
ysionneau: pll + demodulator
<ysionneau>
larsc: does it sound like a very complex project?
<solrize>
ysionneau, this rf is kind of outside the computer zone... but there are some arrl publications? arrl.org
<ysionneau>
for sure I guess I need to buy the PLL since it will operate at high frequency
<ysionneau>
but the rest of the board... I guess I can drop discrete components
<larsc>
there are also demoulators with a built-in pll
<solrize>
ysionneau, larsc does bt gear actually use plls?
<wpwrak_>
PLLs are about as common in modern electronics as electrons :)
<ysionneau>
ah nice , thanks larsc :)
<solrize>
wpwrak_, i dunno, we're talking about something with a design range of a few meters and in fact typical handsfree earpieces work a lot better if you hold the phone closer than keeping it in your pocket
<solrize>
so they are willing to throw away a lot of the signal to keep the hw small and cheap
<solrize>
that's why i was thinking of amplitude detection
<wpwrak_>
solrize: well, you can build an analog radio system, sure. old school :)
<wpwrak_>
not sure how quickly you'll bump into regulatory limit, though. but then if your sender is weak enough, maybe nobody will notice.
<ysionneau>
for GFSK I guess I don't care about the I/Q output, right?
<ysionneau>
I just take one of the two
<ysionneau>
I/Q is useful for QAM, no?
<solrize>
wpwrak_, yeah i was thinking if you make it crappy enough, it doesn't need much hardware
<larsc>
having both makes the demodulation dead easy
<ysionneau>
I/Q is the output of the chip, so it's already baseband, right?
<ysionneau>
so already demodulated
* ysionneau
newbie, sorry
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<larsc>
yes
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<ysionneau>
by trying to understand some analog circuits, I feel I'm putting a toe in an ocean of unknown stuff
<ysionneau>
"what's this ... ?" + wikipedia/google , then end up with explanation which raises another "what's this ?" etc
* ysionneau
affraid
* whitequark
is completely unable to grok analog circuits
<DocScrutinizer05>
>>SDR platforms which allow you to sample at 2.4GHz<< wut?
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<solrize>
those exist but not for bluetooth ;)
<solrize>
they are for fancy pants mobile base stations
<whitequark>
there's some dongle which can sniff bluetooth, but it's absurdly expensive
<DocScrutinizer05>
I doubt *any* SDR is sampling with 4.8Gsamples/s
<DocScrutinizer05>
you always use a Local Oscillator to downbeat-mix the input to some Intermediate Frequency
<DocScrutinizer05>
for <100MHz you might do primary sampling
<larsc>
I meant the baseband pll frequency, not the sampling frequency
<larsc>
but there are also systems that have such a sampling frequency
<DocScrutinizer05>
good luck with processing that data stream in realtime X-P
<wpwrak_>
larsc: every hobbyist should have one of those ;-)
<larsc>
DocScrutinizer05: you'd typically not process it on a CPU
<DocScrutinizer05>
aha
<larsc>
in realtime
<DocScrutinizer05>
so where's the S in SDR then?
<larsc>
in the FPGA
<DocScrutinizer05>
sure, a FPGA easily is processing a datastream of ~10GByte/s, probably via FFT
<DocScrutinizer05>
maybe you get away even with 5GB/s
<sb0>
yeah, and then some more. ask the radiotelescope folks :-)
<DocScrutinizer05>
when using 8bit samples
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<DocScrutinizer05>
ysionneau: I/Q is basically the 90° phase skewed digitized samples of the IF. All (well, most) SDR is based on that
<DocScrutinizer05>
consider sampling a frequency of 2Pi with a A/D that samples (average in) windows of Pi. You'd either get a maximum output signal of +max -max +max... for frequency in phase with sampling, or a 0, 0, 0, when frequency is 90° off in phase
<DocScrutinizer05>
with I and Q sampling with a skew of 90° phase between the two A/D, you have supfficient info about your signal to do SDR on it, no matter what#s the modulation
<DocScrutinizer05>
basically for AM you would do I+Q, for FM you do I-Q (simplified picture)
<DocScrutinizer05>
since sampling at air frequency is simply impossible for all but the highest budget, at e.g. 2.4GHz, you first mix the input frequency with a Local Oscillator in a ring modulator that creates f(in)+f(LO) and f(in)-f(LO) as output
<DocScrutinizer05>
then you usually filter out the f(in)-f(LO) band with a bandpass of a few MHz or kHz width, and then sample it or do analog decoding
<DocScrutinizer05>
you also want to have a bandpass at "antenna" to avoid another input frequency sneak in, f1(in)-f(LO) == f2(in)+f(LO)
<DocScrutinizer05>
that's called the mirror frequency
<larsc>
the trick with I/Q modulators acutally is, that there is no image
<DocScrutinizer05>
often SDR works with mixing down to zero, means LO frequency is (almost) equal to input frequency
<whitequark>
the cake is a lie
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<DocScrutinizer05>
for the LO usually PLL is used (actually an analog oscillator, a reference XTAL oscillator, and two programmable dividers feeding their output to a PLL that adjusts the analog oscillator), which you program to create a LO frequency of f(in)-$some-offset. This $some-offset is the Intermediate frequency you want to use. In shortwave receivers this IF is 455kHz usually, on FM receivers (80-200MHz) it's usually 10.7MHz
<DocScrutinizer05>
so for FM the mirror freq is 2 * 10,7MHz
<DocScrutinizer05>
...off from your intended receiving frequency
<DocScrutinizer05>
you want a bandpass at antenna that gives a sufficient dB attenuation for frequencies that are this far from your center freq, so even strong local transmitters at mirror freq don't interfere with your signal
<DocScrutinizer05>
and you definitely don't want to build all that from discrete components for BTLE ;-)
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<DocScrutinizer05>
when you want to learn about that stuff, maybe RTLSDR is a good starting point
<DocScrutinizer05>
the dongles are still available for a 10 to 20 bucks
<DocScrutinizer05>
and some of them should even be able to reach 2.4GHz
<DocScrutinizer05>
NB that RTL dongles lack most of the filters/bandpasses I mentioned. The cheat on it
<DocScrutinizer05>
they*
<ysionneau>
so I/Q output of the demodulator are still signals at the carrier frequency?
<DocScrutinizer05>
they don't use proper antenna bandpass so mirror frequencies may be a problem, and they don't use IF filter bandpass so the A/D for I/Q is prone to aliasing
<ysionneau>
they are not located after the multiplication of the local oscillator ?
<DocScrutinizer05>
no, they use a downbeat mixer tuner as described above
<DocScrutinizer05>
the tuner output is some Intermediate Frequency of a few MHz which then gets digitized by the RTL2832 chip
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<DocScrutinizer05>
the tuner has the PLL aka LO and the mixer, and some amps
<DocScrutinizer05>
the RTL2832 sends I/Q data to PC via USB
<ysionneau>
ah ok so it lowers the frequency a bit, but not until baseband
<ysionneau>
ok :o
<DocScrutinizer05>
depends on how you program it
<DocScrutinizer05>
"baseband" is not demodulated signal though. What you call "baseband" would be IF of zero
<DocScrutinizer05>
and it's actually usually doing that
<ysionneau>
IF = input frequency?
<DocScrutinizer05>
well, some setups use a very low IF of some kHz or so, to get rid of the DC that sneaks in to I/Q when you mix down to exactl zero
<DocScrutinizer05>
Intermediate Frequency
<ysionneau>
what I call baseband is when you mix the input signal with exactly the carrier frequency (by using a PLL to obtain it, in phase)
<DocScrutinizer05>
the input to the RTL2832, coming from tuner output
<ysionneau>
then you should get your demodulated tone, but centered at 0 Hz
<ysionneau>
instead of centered on the carrier freq
<DocScrutinizer05>
well, modulation not working like this
<DocScrutinizer05>
for AM you might get away with it, yes
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<ysionneau>
yes I think most of my "modulation" thinking is centered on QAM stuf
<DocScrutinizer05>
but then it's pretty hard to filter away the LO signal from your input signal when you mix down to exact 0 to demodulate
<ysionneau>
would you have some litterature to educate me on those topics ?
<ysionneau>
modulation/demodulation
<DocScrutinizer05>
hmm, maybe something comes to mind when I tthink a bit about it
<ysionneau>
on several examples: FSK, QAM all sort of different modulation scheme
<DocScrutinizer05>
right off top of my head I'm short of suggestions
<DocScrutinizer05>
well, those are all already digital modulations
<ysionneau>
book or website (pdf..) whatever
<DocScrutinizer05>
FSK is digital FM
<ysionneau>
I think I can start by digging up my old school book
<DocScrutinizer05>
QAM is digital AM (more or less)
<ysionneau>
yep I got that
<DocScrutinizer05>
sorry, afk
<ysionneau>
I'm mostly interested in digital communications
<ysionneau>
np, thanks :)
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* wpwrak
hates those *_
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<pcercuei>
larsc, hey, do you know an internet provider in Germany that offers contracts without a minimal period?
<larsc>
mnet
<larsc>
that's what I use
<pcercuei>
I didn't know you were into K-pop
<pcercuei>
unless mnet.com is not the right website
<pcercuei>
ah, .de
<pcercuei>
of course
<larsc>
I think I can refer you
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