If you want to filter these signals, and are a ham, I use these on my Raspberry Pi https://www.qrp-labs.com/lpfkit.html and have been heard all around the US daily, and also across both oceans a few times without an amp.
Serial Port SDR
41–50 of 91 posts
Re: Serial Port SDR
#42This is so rad. It's like Tempest, but on purpose. And I love that he hammers it down by filtering out the fundamental and transmitting over 10 feet.
Re: Serial Port SDR
#43Earlier quoted context omitted.
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.
> 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...
Re: Serial Port SDR
#44Earlier quoted context omitted.
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", y…
This is mostly correct, except for FCC exceptions for stuff you build yourself. For example, it is legal to broadcast on the FM band if your signal meets certain signal strength criteria. Also, the FCC itself doesn't do assessments, they are done by independent (expensive) labs.
But the rest of what you say is correct.
Re: Serial Port SDR
#45As 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/
And you can have some serious fun with this with a not-very-powerful computer.
Re: Serial Port SDR
#46> 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.
Not true. Low power FM and AM stations are allowed.
https://www.fcc.gov/media/radio/low-power-radio-general-info...
Re: Serial Port SDR
#47Earlier 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)
Re: Serial Port SDR
#48> 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…
Not true. See https://www.fcc.gov/media/radio/low-power-radio-general-info...
Doesn't require factory built, does not require license.
Re: Serial Port SDR
#49It 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
A YouTube channel called The Thought Emporium has a series about using a sdr called the HackRF to make a radio telescope and a satellite receiver for a few weather sats.
https://www.youtube.com/watch?v=jGWFg7EDnyY&list=PLZLsjPxmF1...
Re: Serial Port SDR
#50Earlier quoted context omitted.
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.
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.