10 ms·

> 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

by lima 8y ago

> 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 you manage to disrupt something important (emergency frequencies, mobile networks...), it's gonna be expensive. Don't try this at home!

jimmytucson 8y ago
I don't think transmitters are made artificially expensive to keep out the newbs. As you said, it's illegal. And if you're a newb (like me) interested enough to try this at home, you might have read to the end of the article where it states: > DISCLAIMER: It should go without saying that you should never transmit on any frequencies or at any power levels for which you are not authorized by the local governing body, but I guess I just said it anyway.
- jimnotgym 8y ago
  Transmitters are not even expensive. A Baofeng is around $20. Some CW kits are $5.
  - subway 8y ago
    Those cheap Baofengs will spew harmonics too. Quality transmitters do get a bit more expensive than the stuff that mostly-works.
poizan42 8y ago
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.
- bluGill 8y ago
  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)
  - wglb 8y ago
    Multiples of 1/4 wavelengths, and if built properly 5/8 wave.
    - naikrovek 8y ago
      ... but 5/8 isn't a multiple of 1/4, Or is that not what you meant?
      - wglb 8y ago
        Right. I should have added more detail. Multiples of 1/8 also work. Now, you can actually make almost any length work with proper tuning circuitry, but the ones mentioned are the most effective.
  - lima 8y ago
    Also, there's a big difference between random noise and a modulated signal on a specific frequency, with a matching antenna. One of those is noise, the other one is a transmission.
- wedowhatwedo 8y ago
  He connected an antenna to it. That's what makes it illegal.
  - poizan42 8y ago
    He connected a regular wire to it... That's kinda how you use a UART.
rkachowski 8y ago
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-information https://www.fcc.gov/media/radio/low-power-radio-general-info...
- wedowhatwedo 8y ago
  Can you quote the FCC regulations that make this transmitter legal? (I'm assuming American law, the law in other countries obviously vary)
  - deleted 8y ago
    [deleted]
  - ac29 8y ago
    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/Documents/bulletins/oet63/oet63rev.pdf https://transition.fcc.gov/Bureaus/Engineering_Technology/Do...
  - wglb 8y ago
    See https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info...
jimnotgym 8y ago
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.
- vvanders 8y ago
  Only for amateur bands. ISM, 2.4Ghz and 5Ghz along with a few others don't require a license.
- wglb 8y ago
  Not true. Low power FM and AM stations are allowed. https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info...
  - lima 8y ago
    And there's ISM bands as well. However, all of these unlicensed bands have strict limits. For any of the fun stuff, you need an amateur radio license :-)
    - andyidsinga 8y ago
      > However, all of these unlicensed bands have strict limits. This is absolutely key here - even in unlicensed bands one cannot just start using the spectrum without careful consideration of regulations for that spectrum. When I was working in the 902-928 Mhz (FCC and similar) and 860s (for ETSI) for RFID we had to do a lot of work to ensure our transmit power, power ramp up, frequency hopping and listen before talk were all implemented properly and demonstrable for certification. It was not trivial.
- jimnotgym 8y ago
  I got called away while writing this earlier and rushed my last point which is clearly wrong. It is too late to edit. Instead: To use a home built transmitter you need amateur radio license, except in certain specific low power situations. To comply with those situations would be difficult without specialised test gear.
xtf 8y ago
And it's nothing new. Same is possible with Raspberry Pi GPIO: https://github.com/F5OEO/rpitx https://github.com/F5OEO/rpitx
- lima 8y ago
  We measured the output of that exact experiment at our local ham radio club and it was horrible, harmonics and noise all over the spectrum.
  - andyidsinga 8y ago
    THIS! -- I was hoping a ham would chime in here :) For anyone looking to do experiments like this - which are really cool to do - getting the ham technician licenses is pretty easy and very educational!
wglb 8y ago
Not true. See https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info... Doesn't require factory built, does not require license.
jstanley 8y ago
You can see from gqrx that his rtl-sdr can barely pick this up when it's 6 inches away on his desk. Somehow I don't think this is causing a significant amount of harmful interference. (Admittedly it is quite a distant harmonic - the actual signal will of course be stronger).

by lima 8y ago

jimmytucson 8y ago

I don't think transmitters are made artificially expensive to keep out the newbs. As you said, it's illegal. And if you're a newb (like me) interested enough to try this at home, you might have read to the end of the article where it states: > DISCLAIMER: It should go without saying that you should never transmit on any frequencies or at any power levels for which you are not authorized by the local governing body, but I guess I just said it anyway.

jimnotgym 8y ago
Transmitters are not even expensive. A Baofeng is around $20. Some CW kits are $5.
- subway 8y ago
  Those cheap Baofengs will spew harmonics too. Quality transmitters do get a bit more expensive than the stuff that mostly-works.

poizan42 8y ago

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.

bluGill 8y ago
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)
- wglb 8y ago
  Multiples of 1/4 wavelengths, and if built properly 5/8 wave.
  - naikrovek 8y ago
    ... but 5/8 isn't a multiple of 1/4, Or is that not what you meant?
    - wglb 8y ago
      Right. I should have added more detail. Multiples of 1/8 also work. Now, you can actually make almost any length work with proper tuning circuitry, but the ones mentioned are the most effective.
- lima 8y ago
  Also, there's a big difference between random noise and a modulated signal on a specific frequency, with a matching antenna. One of those is noise, the other one is a transmission.
wedowhatwedo 8y ago
He connected an antenna to it. That's what makes it illegal.
- poizan42 8y ago
  He connected a regular wire to it... That's kinda how you use a UART.

rkachowski 8y ago

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-information https://www.fcc.gov/media/radio/low-power-radio-general-info...

wedowhatwedo 8y ago
Can you quote the FCC regulations that make this transmitter legal? (I'm assuming American law, the law in other countries obviously vary)
- deleted 8y ago
  [deleted]
- ac29 8y ago
  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/Documents/bulletins/oet63/oet63rev.pdf https://transition.fcc.gov/Bureaus/Engineering_Technology/Do...
- wglb 8y ago
  See https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info...

jimnotgym 8y ago

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.

vvanders 8y ago
Only for amateur bands. ISM, 2.4Ghz and 5Ghz along with a few others don't require a license.
wglb 8y ago
Not true. Low power FM and AM stations are allowed. https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info...
- lima 8y ago
  And there's ISM bands as well. However, all of these unlicensed bands have strict limits. For any of the fun stuff, you need an amateur radio license :-)
  - andyidsinga 8y ago
    > However, all of these unlicensed bands have strict limits. This is absolutely key here - even in unlicensed bands one cannot just start using the spectrum without careful consideration of regulations for that spectrum. When I was working in the 902-928 Mhz (FCC and similar) and 860s (for ETSI) for RFID we had to do a lot of work to ensure our transmit power, power ramp up, frequency hopping and listen before talk were all implemented properly and demonstrable for certification. It was not trivial.
jimnotgym 8y ago
I got called away while writing this earlier and rushed my last point which is clearly wrong. It is too late to edit. Instead: To use a home built transmitter you need amateur radio license, except in certain specific low power situations. To comply with those situations would be difficult without specialised test gear.

xtf 8y ago

And it's nothing new. Same is possible with Raspberry Pi GPIO: https://github.com/F5OEO/rpitx https://github.com/F5OEO/rpitx

lima 8y ago
We measured the output of that exact experiment at our local ham radio club and it was horrible, harmonics and noise all over the spectrum.
- andyidsinga 8y ago
  THIS! -- I was hoping a ham would chime in here :) For anyone looking to do experiments like this - which are really cool to do - getting the ham technician licenses is pretty easy and very educational!

wglb 8y ago

Not true. See https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info... Doesn't require factory built, does not require license.

jstanley 8y ago

You can see from gqrx that his rtl-sdr can barely pick this up when it's 6 inches away on his desk. Somehow I don't think this is causing a significant amount of harmful interference. (Admittedly it is quite a distant harmonic - the actual signal will of course be stronger).