I managed to get the FM transmitter in the N900 working with postmarketOS :D

>check title
Yeah, every phone has radio

@m4iler @martijnbraam Raspberry Pi with a wire on some of the pins can transmit radio using.. searching web.. ah abusing the clock.

@jasper @martijnbraam @m4iler Transmitting that way is not remotely legal, because it's an intentional radiator with emissions all over the place frequency-wise. By the time you add the filtering you need to turn that into a legal transmitter you might as well just buy an already-legal transmitter.

@freakazoid @m4iler was wondering that about @martijnbraam but his signal is so weak the radio can't pick it up a few meter away. (possibly intentionally)

No idea how strong RPi's transmission is..

Presumably the laws about it would specify something about intensity levels..

@jasper @freakazoid @m4iler The FM transmitter in the n900 is very weak so it's legal. Also my FM receiver doesn't have an antenna attached because I live within a few KM of an FM broadcasting tower.

@jasper @martijnbraam @m4iler It's the wire attached to the RPi GPIO pin that I'm concerned about. In the us on the FM broadcast band it's 150 microvolts per meter at 3 meters unless you comply with some other requirements as well (bandwidth, limited transmit time, etc). That's for all of the radiated power, not just the part that's within the band or within the receiver's bandwidth. That's receivable at 3 meters if it's narrowband. Might not be if it's not filtered at all.


@m4iler @martijnbraam @jasper The hackaday article is talking about a range of 100m from a wire hanging off a GPIO pin. While that's achievable with a legal part 15 FM transmitter, it's almost certainly exceeding allowable field strength when transmitting using a square wave, because the allowable field strength is 100 microvolts/meter lower and much of the signal is outside the receiver's bandwidth.

@jasper @martijnbraam @m4iler OTOH in the US it's probably not going to bring an enforcement action at that strength; mostly they're going after people operating at much higher power levels. They might come after them if the neighbors or nearby hams complain about interference, though.

@martijnbraam Suddenly I feel so bad for throwing mine away, although it was in a moment of clarity after replacing the USB connector for the bazillionth time... Kudos!

@raccoon That's why I use an external charger, I barely need the usb connector so it doesn't get damaged so easily.

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