6 ms·

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 th

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.
  - EarthIsHome 8y ago
    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.
    - poizan42 8y ago
      > 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.) The other end is likely a MOSFET with an input impedance on the order of 10 GΩ...
    - tjohns 8y ago
      Wires connected to a closed circuit will radiate too, if you drive them at high frequency. Maybe not efficiently, but it'll still radiate. There's nothing special about an open circuit that makes an antenna work. Shielding (e.g. coax, or a properly grounded enclosure) is what prevents ordinary wires from becoming antennas.
      - StillBored 8y ago
        Normal rs232 is run through shielded cables as well. It was standard practice to wire the d-sub connectors to the cable shields. The wires themselves may not have been shielded, but the cable was shielded against being an antenna.
Animats 8y ago
It's an "intentional radiator", in radio terms.[1] It's very easy to build something that blithers all over the RF spectrum by connecting a digital signal to an antenna. Hook a square wave to an antenna and you're going to get lots of harmonics. This is generally considered a bad thing. In the early days of digital electronics, a TRS-80 Model I home computer and a Milton Bradley Big Trak toy car would both crash if near each other. Strict regulation of RF emissions, and good protection on the input side, is why we can have so many digital devices without everything randomly crashing. [1] https://www.ecfr.gov/cgi-bin/text-idx?SID=56381cb4f24a491e7d0ceb8d3521cefa&mc=true&node=sp47.1.15.c&rgn=div6 https://www.ecfr.gov/cgi-bin/text-idx?SID=56381cb4f24a491e7d...
andyidsinga 8y ago
there is an antenna - just a wire - but that changes the equation a lot relative to what a normal UART does has part of a system that already meets FCC (or other) regulatory standards. I'm curious about the gain of the antenna and what consideration has been made re trasmit wavelength and the antenna wire length.
- gsich 8y ago
  I doubt the gain of a jumper wire is enough to cause any "damage".
  - andyidsinga 8y ago
    You might well be right on that. "damage" would be good to define in general for these kinds of things. I'm guessing the FCC regs talk about this to some degree. So, reality is, this is likely very low-power and likely low-impact experiment and likely not cause a lot of issues with nearby devices that are designed to accept all interference and continue to function or fail gracefully. But IMHO, it is a good idea for anyone doing these kinds of experiments to think a little bit about RF design and the impacts devices might have ..hence my other comment about the value of HAM technicians license & training (which is fun and pretty easy).
- poizan42 8y ago
  I think other commenters have already sufficiently explained this, but just to make it clear: Any wire functions as an antenne, also in a normal circuit where it is connected to something. The length of the wire will cause more radiation from some frequencies, but some designs will have wire length that matches some of the frequencies emitted by the regular communications performed (probably most of them actually - you rarely send random noise over your serial communication channels).
  - andyidsinga 8y ago
    Yep - I totally understand that. I wasn't commenting on wires ability to act as antennas in general - I was commenting on the addition of this wire to the UART for the purpose of wireless comms. That addition is what makes your original point wrong : "Nothing is happening here that doesn't happen already with normal use of the UART"

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.
- EarthIsHome 8y ago
  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.
  - poizan42 8y ago
    > 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.) The other end is likely a MOSFET with an input impedance on the order of 10 GΩ...
  - tjohns 8y ago
    Wires connected to a closed circuit will radiate too, if you drive them at high frequency. Maybe not efficiently, but it'll still radiate. There's nothing special about an open circuit that makes an antenna work. Shielding (e.g. coax, or a properly grounded enclosure) is what prevents ordinary wires from becoming antennas.
    - StillBored 8y ago
      Normal rs232 is run through shielded cables as well. It was standard practice to wire the d-sub connectors to the cable shields. The wires themselves may not have been shielded, but the cable was shielded against being an antenna.

Animats 8y ago

It's an "intentional radiator", in radio terms.[1] It's very easy to build something that blithers all over the RF spectrum by connecting a digital signal to an antenna. Hook a square wave to an antenna and you're going to get lots of harmonics. This is generally considered a bad thing. In the early days of digital electronics, a TRS-80 Model I home computer and a Milton Bradley Big Trak toy car would both crash if near each other. Strict regulation of RF emissions, and good protection on the input side, is why we can have so many digital devices without everything randomly crashing. [1] https://www.ecfr.gov/cgi-bin/text-idx?SID=56381cb4f24a491e7d0ceb8d3521cefa&mc=true&node=sp47.1.15.c&rgn=div6 https://www.ecfr.gov/cgi-bin/text-idx?SID=56381cb4f24a491e7d...

andyidsinga 8y ago

there is an antenna - just a wire - but that changes the equation a lot relative to what a normal UART does has part of a system that already meets FCC (or other) regulatory standards. I'm curious about the gain of the antenna and what consideration has been made re trasmit wavelength and the antenna wire length.

gsich 8y ago
I doubt the gain of a jumper wire is enough to cause any "damage".
- andyidsinga 8y ago
  You might well be right on that. "damage" would be good to define in general for these kinds of things. I'm guessing the FCC regs talk about this to some degree. So, reality is, this is likely very low-power and likely low-impact experiment and likely not cause a lot of issues with nearby devices that are designed to accept all interference and continue to function or fail gracefully. But IMHO, it is a good idea for anyone doing these kinds of experiments to think a little bit about RF design and the impacts devices might have ..hence my other comment about the value of HAM technicians license & training (which is fun and pretty easy).
poizan42 8y ago
I think other commenters have already sufficiently explained this, but just to make it clear: Any wire functions as an antenne, also in a normal circuit where it is connected to something. The length of the wire will cause more radiation from some frequencies, but some designs will have wire length that matches some of the frequencies emitted by the regular communications performed (probably most of them actually - you rarely send random noise over your serial communication channels).
- andyidsinga 8y ago
  Yep - I totally understand that. I wasn't commenting on wires ability to act as antennas in general - I was commenting on the addition of this wire to the UART for the purpose of wireless comms. That addition is what makes your original point wrong : "Nothing is happening here that doesn't happen already with normal use of the UART"