Can someone with understanding of the matter ELI5 why this matters?
[deleted]
Serial Port SDR
31–40 of 91 posts
Re: Serial Port SDR
#32Earlier quoted context omitted.
From the article, the effective range seems to be around 10 feet. IIRC you are generally permitted to use whatever frequency you wish within a very limited radius as long as it is for "research purposes" Edit: this last point is wrong, as mentioned below exemptions seem to apply for certain frequencies with a low powered device https://www.fcc.gov/media/radio/low-power-radio-general-info...
Can you quote the FCC regulations that make this transmitter legal? (I'm assuming American law, the law in other countries obviously vary)
The FCC regulations are very long, hard to understand, and occasionally contradictory - I know, I work in the industry. The closest section of the law that comes to mind is for very low power (typically under 1mW) devices that do not require the user to have a licence. These are so called "part 15" devices, which refers to the Code of Federal Regulations (CFR) Title 47, Part 15.
While the user of these sorts of devices doesn't require a licence, the device itself needs to be certified, so that, among other things, it doesn't spew noise all over the RF spectrum. This device wouldn't pass.
There are also experimental licences that can be held by businesses such as RF equipment manufacturers that allow for using equipment that hasn't yet received FCC approval. They are usually band restricted, geographically restricted and power restricted, and you must take care to not have high levels of spurious emissions.
edit: Here's a PDF explainer on Part 15 devices: https://transition.fcc.gov/Bureaus/Engineering_Technology/Do...
Re: Serial Port SDR
#33Reminds me of using an output pin on Raspberry Pi to transmit FM radio: http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry...
Reminds me of abusing the CRT on the TRS-80 to play "music" on an AM radio. Except we were kids and had very little idea what we were doing.
Re: Serial Port SDR
#34As mentioned in the first sentence, the RTL-SDR project is out there. You can easily buy a $20 USB Software Defined Radio with software that will handle everything for you and lets you play around with an SDR: https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/
Re: Serial Port SDR
#35> This alone is impressive, but [Ted] isn’t done yet. He realized that this method of transmission was generating some strong frequency harmonics which extended far beyond the theoretical maximum 1 MHz frequency of his UART SDR. i.e., blast noise all over the spectrum. There's a reason why real transmitters are more expensive than a serial port adapter. This kind of RF pollution is illegal for obvious reasons and if…
And it's nothing new.
Same is possible with Raspberry Pi GPIO:
Re: Serial Port SDR
#36> This alone is impressive, but [Ted] isn’t done yet. He realized that this method of transmission was generating some strong frequency harmonics which extended far beyond the theoretical maximum 1 MHz frequency of his UART SDR. i.e., blast noise all over the spectrum. There's a reason why real transmitters are more expensive than a serial port adapter. This kind of RF pollution is illegal for obvious reasons and if…
The harmonics are above the transmission frequency, so a low pass filter is normally all that is needed to clean this up. There is a project that uses a Raspberry pi to transmit from is GPIO To use a home built transmitter you need amateur radio license, no matter what.
Only for amateur bands. ISM, 2.4Ghz and 5Ghz along with a few others don't require a license.
Re: Serial Port SDR
#37USB serial dongle? pah, use the system-bus on the motherboard ;) https://github.com/fulldecent/system-bus-radio
Re: Serial Port SDR
#38Earlier quoted context omitted.
He connected an antenna to it. That's what makes it illegal.
He connected a regular wire to it... That's kinda how you use a UART.
The wire is being used as an antenna. When you use UART, you have the other end of the wire terminated with another circuit. (i.e. The energy goes to into the connecting circuit.)
Because the wire ends at an open circuit, the currents on the wire radiate, turning the wire into an antenna.
Re: Serial Port SDR
#39Earlier quoted context omitted.
But he doesn't have any amplification. Nothing is happening here that doesn't happen already with normal use of the UART. If what he is doing here is illegal then the RF pollution from using the UART normally would be too.
He didn't say this, but I suspect that his antenna was that specific length for rf reasons - wires work best as antennas when their length is some multiple of the wavelength. (ask an rf engineer if you want details, I'm close enough for discussion but all rf engineers will cry when they read that)
Multiples of 1/4 wavelengths, and if built properly 5/8 wave.
Re: Serial Port SDR
#40I have a converter that I plug into my USB socket and then I can plug my old style keyboard into this converter. Is that what is being talked about here? The picture looks different.
Not sure what is inside of one of those keyboard adapters, but this is something called a serial adapter (or, more precisely, UART adapter). It is usually used to program microcontrollers (read Arduinos), so everyone dabbling with those (typical audience of hackaday.com) probably has at least one at home, they cost like $2-3.