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Serial Port SDR

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21–30 of 91 posts

Re: Serial Port SDR

#21
post #12

Well now we know what radio waves are produced by 0x55. How about other characters? I'm willing to bet that everyone's wired keyboard is an SDR so to speak and a well placed receiver can keylog you.

I wonder how fast you could toggle the capslock LED... hmm

Re: Serial Port SDR

#22
post #10

> 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…

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)

Re: Serial Port SDR

#23
post #10

> 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…

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 connected an antenna to it. That's what makes it illegal.

Re: Serial Port SDR

#24
post #10

> 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…

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)

Re: Serial Port SDR

#25

Earlier 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 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.

Re: Serial Port SDR

#26

Earlier 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)

[deleted]

Re: Serial Port SDR

#27
post #7

It sounds interesting. Beyond controlling RC vehicles, what would be some applications of software defined radios (SDRs)? By the way, it looks like a USB-VGA dongle can be manipulated in a similar way: https://news.ycombinator.com/item?id=16907260

There are not many commercial applications because it is usually much cheaper to implement in hardware and flexibility is not important.

Re: Serial Port SDR

#28

Earlier 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 connected an antenna to it. That's what makes it illegal.

Ugh. It's not by default "illegal", unless it provably violates Part 15.

Has a Part 15 assessment been done yet? Have we analyzed power emission levels to assert that this thing is indeed 'breaking the law'?

Has this device been checked by the FCC for spurious emissions during normal operation? Did it pass, or is it chinese jank uncertifiable garbage?

Edit: C'mon downvoters. If you make a claim that it's "Illegal", you need to have some sort of proof that its the case. And I'm not immediately seeing it. Further research? Sure.

Re: Serial Port SDR

#29
post #10

> 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.

Re: Serial Port SDR

#30
post #7

It sounds interesting. Beyond controlling RC vehicles, what would be some applications of software defined radios (SDRs)? By the way, it looks like a USB-VGA dongle can be manipulated in a similar way: https://news.ycombinator.com/item?id=16907260

We used to half joke that graphics card is in fact nothing more than very good and cheap DDS signal generator.

And as for SDR applications: most of modern radio devices use software defined radios and many modern radio interfaces cannot be reasonably implemented in any other way.

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