Imagine you’ve got an FM transmitter located some place. Wouldn’t it be mighty convenient if you could control that transmitter remotely? That way, you wouldn’t have to physically attend to it every time you had to change some minor parameters! To that end, [Ricardo Lima Caratti] built a rig to do just that.
The build is based around the QN8066—a digital FM transceiver built into a single chip. It’s capable of transmitting and receiving anywhere from 60 MHz to 108 MHz, covering pretty much all global FM stereo radio bands. [Ricardo] paired this chip with an ESP32 for command and control. The ESP32 hosts an HTTP server, allowing the administration of the FM transmitter via a web browser. Parameters like the frequency, audio transmission mode, and Radio Data Service (RDS) information can be controlled in this manner.
It’s a pretty neat little build, and [Ricardo] demonstrates it on video with the radio transmitting some field day content. We’ve seen some other nifty FM transmitters over the years, too. Video after the break.
Doesn’t an FM broadcast band license require an on-site licensed engineer to be present during operation hours? Maybe my information is out of date…
probably the rules are different in brazil
Info on FCC license: https://www.fcc.gov/media/radio/low-power-radio-general-information#UNLICENSED
Reading headline, turned my mind immediately to … Well … Your mind probably went there too.
Radio Caroline without the swim in the Atlantic?
more like middle east, flip up lid, press red button, … sort of thing …
Sadly, not legal where I am.
outside of authorized band, even for “unlicensed”, and remote control of a transmitter is also potential issue.
A friend of mine, formerly a real estate agent, once told me about a system he used called “Drive Buy Radio”. It was a low power FM transmitter that was used to broadcast a recording which extolled the virtues of the property for sale. I seem to recall that he said no license was required to operate the transmitter. This was in the US.
I imagine that the internet has obviated such systems, but there are still some hanging around, e.g. https://jrgelectronics.com/product/drive-buy-radio-1000/
Other evidence in a link that’s a little less likely to disappear by the time you read this:
https://www.gettyimages.in/detail/news-photo/drive-buy-radio-real-estate-to-revolutionize-the-business-news-photo/1079848748
Licensed briadcast babd transmitters. AM FM, TV have been authorized for unattended remote control for years. Type acceptance and authorization is required, as well as auto shutdown in case of put of parameter operations
FCC part 15 allows unlicensed operation on the broadcast bands (in the US) at extremely low power.
This would certainly not be legal for licensed operation because homebrew transmitters not permitted. Now if this could be made to control a proper transmitter (and you held the necessary license)…
In Brazil, FM transmitters with very low power (up to 0.5 mW) and short range can operate without a license, typically in restricted bands like 76-88 MHz, while commercial FM operates in the 88-108 MHz range. Wireless microphones are legal if they comply with designated sub-bands and power limits to prevent interference. Community radio stations, limited to 25 watts and a 4 km radius, require licenses granted to non-profit organizations through the Ministry of Communications, with permits valid for 10 years and restrictions on commercial advertising. Commercial FM stations must participate in public auctions and follow technical regulations set by Anatel, Brazil’s telecom regulator, ensuring proper spectrum use and public service obligations.
The FCC permits unlicensed FM transmitters at powers below 250µv/m measured 3 meters away. This works out to about 10 nanowatts, and an effective radius of about 200 feet.
https://docs.fcc.gov/public/attachments/DOC-297510A1.pdf
Honestly though, that’s pretty useful. Pipe your podcasts through such a transmitter and you can listen on any old radio in the house — the Delco ripped out of a Chevy and mounted to a shelf in the garage, the Sony stack in the living room, the Lasonic boombox by the pool.
All at the same time, if you feel like it, because there’s no codec delay, so they’re not annoyingly out of sync. It’s an elegant way to do, using old tech, what Sonos somehow managed to make modern but awful.
It is important to emphasize that the project presented here is not intended to encourage anyone to violate their country’s regulations regarding radio frequency emissions. In the project’s documentation, I specifically warn against such practices. The goal of this project, centered around an Arduino library for controlling the QN8066, is to facilitate the development of diverse solutions involving this device.
In Brazil, for example, FM transmitters with very low power (up to 0.5 mW) and short range can operate without a license, typically in restricted bands like 76-88 MHz, while commercial FM operates in the 88-108 MHz range. Wireless microphones are legal if they comply with designated sub-bands and power limits to prevent interference. Community radio stations, limited to 25 watts and a 4 km radius, require licenses granted to non-profit organizations through the Ministry of Communications, with permits valid for 10 years and restrictions on commercial advertising. Commercial FM stations must participate in public auctions and follow technical regulations set by Anatel, Brazil’s telecom regulator, ensuring proper spectrum use and public service obligations.
Essentially, this chip is a glorified Mister Microphone and an FM transmitter using this chip would never meet the technical requirement set forth in part 73. Unfortunately, most of the cheap Chinese FM transmitters use this chip or something similar. A analog broadcast quality FM transmitter uses a very linear VCO exhibiting very low phase noise, an optimized loop filter and a PLL IC controlled by an MCU to perform the frequency synthesis for the transmitter. More contemporary transmitters use DDS and DSP to achieve the same function.
Part 15 has been used as a club by the FCC in their pursuit of unlicensed FM broadcasters for years. Part 15 does not apply to unlicensed broadcast stations. It only applies to intentional radiators (garage door remotes, Mr. microphone, etc.) and unintentional radiators (EMI from computers and such). Broadcast stations both licensed and unlicensed are subject to Part 73.