APRs is an amateur radio protocol allowing the exchange of short packets of data. It’s commonly used to transmit a GPS position, though it can find other applications. The Flipper Zero RF hacker’s multi tool normally needs to be hooked up to an external transmitter to do APRS, but [Richard YO3GND] has made his Flipper do the job without any external parts at all.
One of the the Flipper’s radios sits in the 435 MHz ISM band, meaning that the rest of the 70 cm amateur band is well within its reach. There only remains the subject of modulation, in which the Flipper’s FSK and APRS’s FM are similar on paper if not on a waterfall display. Some software hackery ensues, and the Flipper is an APRS station. Because of the FSK-as-FM modulation it won’t be decoded by everything, but you can’t argue with the bill of materials if you happen to own a Flipper. Check out the demo video below.
Meanwhile, should any readers with an amateur radio licence be interested, this certainly isn’t the first time we’ve brought you a minimalist APRS transceiver. Assuming that possession of a Flipper hasn’t got you into hot water, that is.
That’s cool, but real APRS uses VHF and AX.25 UI frames @1200 Baud FSK. :)
Sure you mean AFSK.
Hi, yes, strictly speaking. If it’s using audio signals, FSK becomes AFSK.
But it’s same thing in the end (on RF; it’s both same waveform).
Transceivers with a dedicated Packet/Data/FSK connector on the back do support 9k6 TNCs, for example.
This also works if its operating in 1k2 (if it has an 1200 Baud modem installed).
In the past, such a direct FSK connector was meant for proper RTTY operation.
But both 1200 Baud Packet and 45,45 Baud RTTY can also be used via Mic-in and Speaker-out of a radio.
Then it’s using AFSK instead of FSK, basically. The audio signal modulates the radio signal.
We did use that connection method on CB radio often (Germany/Austria/Swiss), because we couldn’t legally modify the CB radio.
Anyway, if the frequency is using FM (such as APRS on 144,800 MHz in Europe), then tapping the FM discriminator is a good thing.
Because using normal loudspeaker output alters the frequency response, which TNCs don’t like.
fAX.25 too ;)
I probably struggle from sound sensitivity but I know I’m not alone. Despite really liking the idea from such a brilliant guy, I can’t watch a video loud background music and this AI voice. I apologize for this unsolicited rant.
Please keep bringing up valid quality concerns. Internet ‘content’ is just turning into click bait slop, and the worst part is people act like information and entertainment quality is IMPROVING.
My current theory is that the people who think that YouTube is full of high quality content (and somehow don’t mind click bait titles/ thumbnails unrelated to the videos etc) are people who watch television, and are comparing it to really bad entertainment with ads running at least a third of the time.
We need to keep complaining. People need to stop accepting this garbage as normal.
I have been using PWM on FSK and relying on the FSK filtering to produce audio FM modulation on the SX1276. This is demodulating as voice on an HT at 70cm. Probably could get AFSK like this.
PWM -> DIO 2 -> sx1276/fsk -> antenna -> HT -> my ear.
SDR shows acceptable FM modulation.
Well that’s pretty cool
70cm APRS isn’t very common in the US, but there are a few digipeaters around. They usually use 9600 baud FSK though.