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thanks jonny. i'll just repost my question from the idiot thread any recommendations for a book about radio, with an emphasis on SDR? i've got a mathy background so lots of math is ok by me. i got a little DVB-T type dongle/SDR for christmas and i'm going to gently caress around with it and see what kind of signals i can catch on my 3rd floor apartment. i've got the dongle plus a dipole antenna with long/short extendable antennas. i think it's more of a "toy" but i've got some software on my mac and i'm going to see how far i can get with this thing.
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Jan 2, 2021 00:43
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| # ¿ Apr 29, 2024 07:36 |
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thanks! i tried out the gqrx and it worked on my mac. ive been loving around with gnuradio too. i was confused about the drivers though. i just got both of them packaged as applications, so they both have librtlsdr inside the package (well i know gnuradio said they did it that way). is that the driver or is there a deeper macOS library i need to gently caress with? but yeah ill take a look for some of the weaker signals. i can get the local npr station pretty well and i can pick out the digital signals (haven’t gotten to decoding them yet), but i don’t yet know where to look for more interesting things. shortwave stuff may be a long way off for me. ive got a balcony but it’s not that big so im limited in how long of an antenna i can put up. the railing is metal too so i don’t know how much that could cause interference.
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Jan 2, 2021 02:36
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lol my apartment directly overlooks the leasing office so i can't do poo poo without them immediately noticing. there's a guy in the neighborhood that has what i assume is a big HAM tower. 
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Jan 2, 2021 23:25
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look its capitalized in the title so i'm just following the style guidelines
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Jan 3, 2021 05:30
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so some kind of band-pass filter? is that the same effect for an FM signal like this?  (also not sure what that little spike is on the left, there's also a bit on the left edge of the digital band as well)
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Jan 8, 2021 03:58
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Jonny 290 posted:Ideally if you want to use one of the rtl sdr "v3" sticks (which have built in shortwave functionality) on lower frequencies, you'd put a box that is a combo antenna matcher and attenuator in front of it, because it has no gain controls down on AM/shortwave. everything is full throttle. and as a result, since AM broadcast signals are like 10000x stronger than weak shortwave ones, the former just overloads and you hear local nazi sports talk radio every 10khz. They do very well when you have a preselector or attenuator ahead of them, between the SDR and the antenna. i've been thinking about this a little bit. do you get the repeating signals because the input is so big that it's clipped (and if it's clipped you obviously just lose any small signal on top of it)? if that's the case i get why you'd get higher frequencies than the fundamental since you've got some kind of square wave but how do you end up with lower frequencies? edit: ok nevermind, i was confused. i was trying to understand the image i posted earlier but i think that just has to do with stereo FM radio broadcasting and no weird extra harmonic poo poo. Eeyo fucked around with this message at 03:26 on Jan 14, 2021 |
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Jan 14, 2021 03:12
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Stack Machine posted:Are you talking about the stripes above and below the main FM channel? That's digital HD radio carefully tucked into the guard bands of the original FM radio standard. no i mean when there was no audio transmitted i could see several distinct frequency components that were evenly spaced by ~20kHz. i gather that's the 19kHz stereo pilot tone, but i'm picking up copies at 2*19, 3*19, etc. i was expecting there to just be the carrier frequency when the transmission was silent and was puzzled why i saw so many of them.
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Jan 14, 2021 05:45
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what do you mean post sticking out? like in the insulator/conductor part in the middle, or an extra knob on the ground? that's definitely a bnc female, it has an insulator with a cylindrical hollow conductor in the middle. the conductor doesn't really go 'in' like in a lot of other female connectors, the insulator/conductor has some prominence from the base of the connector, but is shorter than the grounding around it.
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Jan 31, 2021 21:31
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| # ¿ Apr 29, 2024 07:36 |
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just compiled the rtl_433 thing. i can see a bunch of random temp sensors, presumably just houses in the neighborhood or something? i was loving around with the frequency and now im seeing a few tire pressure monitors. i uhh never thought about it but i guess you’d have to send out the data somehow if you’ve got an actual pressure sensor inside a wheel. wonder what kind of range those things have. i can see 2 unique ids, but i guess each tire could have a unique id so maybe im just picking up the closest front tires in my parking lot or something.
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Feb 9, 2021 03:08
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