whitequark changed the topic of #tinyqma to: design of an open hardware DDS-based QMA with a low-voltage dc/rf stage :: http://irclog.whitequark.org/tinyqma
<bofh__>
claim: if you're working on SDR anything near computers, eventually you'll run into some form of puzzling behaviour whose cause was "accidentally picking up some harmonic of the ethernet clock".
<whitequark>
that sounds plausible.
<whitequark>
there's so much EMI around computers. I made an AM radio, there's been no AM stations, and the only thing it was picking up is clock harmonics
<whitequark>
and holy fuck there is a lot of clocks
<whitequark>
you could practically compose music by scrolling through different screens on my android phone
<bofh__>
so I can reliably tell when my downloads finish on my laptop because the general colouring of the hiss in the speakers changes
<bofh__>
also becomes much quieter, but I notice the pitch change more
<bofh__>
ethernet's one of the strongest, in my experience
<bofh__>
also it's at a nice freq - 25M for 10/100, 125M for GigE
<whitequark>
my laptop's power supply hisses depending on power consumption
<bofh__>
so you're likely to run into it all over the place (i.e. right now I'm running into its 5th harmonic in the marine VHF band)
<whitequark>
I can discern video downloading, LLVM compiling, ...
<bofh__>
mine does too, but it's really quiet. I practically have to have my ear on top of it.
<whitequark>
yay poorly potted inductors
<bofh__>
it creeped me out the first I heard it, because it was very distinctively a hiss
<bofh__>
no tonal components
<whitequark>
the stock one is very quiet. the external one (but still official) is loud
<bofh__>
and I couldn't figure out what the hell was generating it.
<bofh__>
then yeah poor potting
<whitequark>
I can hear most power supplies
<whitequark>
well, maybe not most, but a lot of them
<bofh__>
I'm glad LCDs became popular
<whitequark>
lol
<whitequark>
I have a board, arduino-like shield, with an LCD
<bofh__>
so many years when I frantically wanted a notch filter around 15.7kHz
<whitequark>
and it doesn't even hiss, it whines
<bofh__>
when I was younger I could hear TV flyback from *outside people's houses*.
<whitequark>
wow
<bofh__>
(since then I've lost quite a bit of high-freq hearing, but apparently can still hear up to 19.5kHz fine according to an official test)
<whitequark>
that shield, I don't understand. either they have not turned it on once before shipping, or they are completely deaf
<whitequark>
because it is loud and absolutely unbearable to hear
<bofh__>
that's amazing
<bofh__>
I really want to know how they even managed that
<whitequark>
this is actually an achievement, I know few sounds that are just as annoying as that one
<bofh__>
also, just submitted the ublox gps chipset on this transmitter to the gpsd hall of shame
<bofh__>
""features"": disregards ionosphere correction parameters from almanac, does not store ephemerdies at all, always uses 91/-181 as its starting lat/lon
<bofh__>
this means with a crappy antenna your full site survey can take...oh... about 7 hours.
<whitequark>
wow, wtf
<bofh__>
and because of how they designed the firmware, the VHF marine transmitter will not transmit until a GPS lock is attained. this is a feature to prevent it from accidentally transmitting because you can leave the GPS antenna off and it won't transmit
<bofh__>
coupling data from acoustic hydrophones that report whale location to AIS transmissions that notify ships of movements and areas to be avoided (after writing detection routines for the acoustic hydrophone data)
<bofh__>
I had 6 months to burn between when I finished my master's and when I start my phd, so
<whitequark>
oh, neat
<bofh__>
they already had this equipment in place, otherwise I would have just recommended to buy a USRP B200 instead
<bofh__>
AIS is such a clusterfuck btw
<bofh__>
(also part of this was developing an AIS protocol receiver for rtl_sdr)
<bofh__>
also rewriting the terrible (windows-only, unsigned) driver for the hydrophones as a libusb driver instead
<whitequark>
so the usual
* whitequark
sighs
<whitequark>
trying to hire a programmer, browsing local resume databases
<whitequark>
there are two particular kinds of people
<whitequark>
the first says "programmer. remote work. i have a car and driver's license"
<whitequark>
i mean, WHAT
<whitequark>
the second says "programmer. 5 years experience" and that is all
<whitequark>
sometimes literally these four words
<whitequark>
no mention of the tech you used. nothing whatsoever. just "a programmer"
<bofh__>
wow
<bofh__>
not even specifying what those 5 years experience are in?!?
<whitequark>
yep.
<whitequark>
like 70% of people are trained exclusively or almost exclusively in the local equivalent of SAP, too
<whitequark>
a particular combination that i encounter a lot is something like
<whitequark>
"c++ (basic), html, css"
<whitequark>
and that's all.
<whitequark>
i'm like ???
<whitequark>
oh i know. high school curriculum used to have C++, maybe still has
<bofh__>
they teach CSS in high school?
<whitequark>
actually, they did in mine
<whitequark>
HTML, CSS, a bit of JS, LaTeX
<whitequark>
you're not surprised to see C++ there though?
<bofh__>
it's a godawful teaching language
<bofh__>
but I could see it in there on the basis of "INDUSTRY!!!"
<whitequark>
that's how it went pretty much
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<bofh__>
turns out CS-related bullshit is spatially invariant, who knew.
<bofh__>
let's play a game of coding techniques I never, ever want to see in my life again
<bofh__>
I'll start with "people calling exit() in their LIBRARY CODE".
<bofh__>
it's like oh hey this function got passed a window length larger than the FFT filter size, oh no problem I'll just scale it down to OH WAIT I CAN'T, BECAUSE MY PROGRAM JUST QUIT.
<whitequark>
solution: add an at_exit function, longjmp out of it
<whitequark>
ship it
<bofh__>
that's a terrible idea. I like it.
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