blinry

blinry, 2 months ago

@clx Ohh! Cute how their logo resembles the shape of the signal!

blinry, 2 months ago

@vampirdaddy This one even has an upconverter built-in \o/

blinry, 2 months ago (edited 2 months ago)

44: Detect when a smartphone is turned on

I was curious whether I could see the NFC transceiver in my smartphone!

And yeah, especially using my random wire antenna, this works really well!

My smartphone seems to emit at the NFC frequency a couple of times per second.

And when unlocking the screen, it emits five very strong beeps on that frequency! I can see those from the other side of our apartment.

Surely, these signals are the same for every device, right? 😶

Observe the five beeps here:

blinry, 2 months ago

45: Communicate wirelessly using a book

@piko and I played around with NFC a bit more, and we found out that when getting close to a tag, a smartphone emits at 13.56 MHz continuously!

So, we sent Morse code to each other between rooms, using a smartphone and a library book! :'D

Take that, Bundesnetzagentur!

Seems that the shortest signal you can create is 70 ms long, resulting in a meager communication speed of ~10 words per minute…

blinry, 2 months ago

@haifisch Yeah, got a signal from NOAA in entry number 33! \o/

blinry, 2 months ago

@Manu Ohh fun! Where are you, if you wanna tell?

blinry, 2 months ago

@LucasWerkmeister I happens every time you unlock the screen!

blinry, 2 months ago

46: Receive navigational aids for airplanes

There are ground stations that emit a signal that allow calculating your angle relative to it! If you receive two, you can determine your position.

I hear the one close to Hamburg! SDRangel has a decoder, of course! It outputs angles between 210° and 230°, which is pretty good! Don't think they are meant to be used from the ground.

The neat navigational map is from https://skyvector.com!

(Thanks, @fly_it!)

An aeronautic navigational chart.
A map where I show that the real angle is 224 degrees.

blinry, 2 months ago

I spent ages trying to build my own decoder in GNU Radio. But I wasn't familiar with it at all, and I eventually gave up. Still, that seems to be the software you wanna learn for tasks like these!

By the way, how the ground stations work is fascinating: In my case, it's a "Doppler VOR": It transmits a static frequency via amplitude modulation, and adds another signal that moves around in circles, so you get a Doppler frequency shift.

If you compare the two, you can calculate the angle!

image/png
image/png

blinry, 2 months ago

@b4ux1t3 Will eventually be a blog post, I think, yeah! :)

blinry, 2 months ago

47: See how low you can go in the frequency spectrum

This was a fun exploration: What's the lowest-frequency broadcast I can receive?

The RTL-SDR Blog V4 stick I'm using has a neat feature – a built-in "upconverter", which is enabled automatically when you try to listen to frequencies below what the chipset supports. This allows it to receive down to ~500 kHz!

The first stations that are comprehensible start at 1 MHz for me.

I scroll through the waterfall diagram and click on things.

blinry, 2 months ago

@flxtr Haha :D It was yet another name that fit that schema!

blinry, 2 months ago

48: See how high you can go in the frequency spectrum

My SDR stick has a maximum sampling rate of 3.2 megasamples/s, so by Nyquist's theorem, that means that the highest frequency it can theoretically measure is 1.6 GHz.

It seems pretty quiet up there, probably because I lack proper antennas. I found these three lines in an amateur band, but they probably originate from the stick itself, or another device.

So the highest-frequency thing I've received is ADS-B at 1090 MHz (see entry #5)! 🎉

blinry, 2 months ago

49: Listen to marine radio

We've been over this. Not allowed in Germany. Don't do it. ⛔

But if you're in the US, anyone can purchase a marine radio, and even use it to transmit! :D

blinry, 2 months ago

@manawyrm Ohhh, interesting! Thanks for the explanation!

blinry, 2 months ago

50: Go mobile!

Just now, I was wondering whether there are any Android apps for controlling SDRs.

And it turns out, the software I liked best this week, SDR++, has an Android version since a couple of weeks! \o/ https://www.sdrpp.org/nightly

So now I can go track down the source of some of these strange signals! :3

blinry, 2 months ago

And with that, … 🥁 … I'm officially done with my "50 things to do with a software defined radio"! 🎉

This was seven very intense days, where I've learned a lot of new things about radio waves and the many things they can be used for!

I'm proud! I'm tired! I'm amazed that all those things I received are all around us, everywhere, all at once! :O

Thanks for following along, everyone! I'll probably make a blog post and/or talk out of this series, sometime in the future!

blinry, 2 months ago

Here's some things that I haven't tried or that haven't worked:

• Receiving digital voice modes (SDRangel should be able to do it, but I couldn't figure it out)
• Receive something from the ISS
• Use the GRAVES radar to detect meteors (couldn't detect it)
• Receive videos on ham bands
• Receive Iridium satellites
• Listen to pirate stations
• Receive Cubesats

Also, doing things with Wi-Fi/Bluetooth/Zigbee could be fun, but I'd need a more expensive receiver for those frequencies.

blinry, 2 months ago

So, was this project in fact a gateway drug to getting an amateur radio license?

Yeah, probably. I'd love to transmit something and experiment more! :D

In Germany, a new license class will be introduced this summer, that'll allow you to send on the 10-meter, 2-meter and 70-cm bands (the "N class").

In fact, there's a really good online course that teaches you everything you need to know: https://50ohm.de Highly recommended, even if you're not planning on getting a license.

blinry, 2 months ago

@dj3ei Ohh, I was wondering why there was an "ES" in there, thanks!! The 73 I recognized :)
@manawyrm

blinry, 2 months ago

@basti Whoa, which one is that? :O And what do you wanna do with it?

blinry, 2 months ago

@pebbe Apparently 🤷

blinry, 2 months ago

@franckmee Super interesting, thanks! Happy that I could receive it anyway – I'm one floor below ground level, but behind many buildings.

blinry, 2 months ago

@Cqoicebordel To include that data, and a quick start, is a really good idea! :)