A little USB sound card is passed through to the VM and it's been rock solid for about 2 years now. I use it exclusively as a Spotify chromecast type thing that cost me about $3.50 in parts.
The README goes over this, but if people keep blindly ignoring it, expect regulators to figure out a way to make our lives a lot less fun.
(tl;dr: The output of these "transmitters" contains spurs you're not equipped to detect but which can indeed be problematic for others. Transmitters are regulated for sound physical reasons, some which are enumerated here.)
The range at which your FM receiver can pick up an FM signal may indeed be ten feet, but that's a product of the transmitter power, the transmit antenna gain, the path loss, the receive antenna gain, and the receiver sensitivity. To infer anything about one of those parameters (for this discussion, the transmit power), you have to know the other four, and you don't. (And neither do I. Even the measurements I'm equipped to make require a lot of assumptions and have significant uncertainty.)
Secondly, FM (radio folks would call this wide-FM) is particularly power-hungry because it occupies a relatively wide swath of bandwidth. Typically limited to 75kHz and in practice somewhere around 50 for analog stereo or just shy of 60 with RDS (which pifmrds can do). For example, a 104.3MHz station is actually transmitting anywhere between 104.225 and 104.375 at any given instant. This means that the receiver has to demodulate the carrier which may be varying all over that range, and it requires a fairly strong signal to do that. If the FM receiver loses lock, it doesn't mean the signal doesn't exist, merely that it's below the receiver's sensitivity.
Other spectrum users, like radar for example, may be dramatically more sensitive, and pick up a signal of the same strength many miles away. A mode that occupies less spectrum generally requires less power. They may also have better antennas (radar dishes tend to be tightly focused, that's the whole point), better receivers (local self-noise can be minimized through careful-but-costly engineering), et cetera.
They may also be above you, so while you see the signal disappearing as soon as you get on the other side of some hedges, there's no foliage between you and an airplane.
So while _for you_, the effective range may be ten feet, but for someone else, the signal may be a problem dozens of miles away.
Furthermore, and the whole point here, is that you're not just interfering with other users in the 88-108MHz FM broadcast band. (If you were, frankly, I wouldn't care one bit; there's little actual harm to be done.) It's that as a digital pin being bashed up and down at those frequencies, the resulting signal is profoundly not sinusoidal. It has much faster rising and falling edges, which mean the signal has plenty of energy in harmonics, not just the fundamental frequency of the carrier. My spectrum analyzer only goes to 2.7GHz and I was able to see (admittedly diminishing) energy up beyond 1GHz, which is both impressive in that the BCM chip's GPIOs can slew that fast, and terrible in that you're interfering with _everyone_ when you do it.
So, say you've told pifm to transmit at 88MHz, right at the bottom of the broadcast band where off-the-shelf receivers can pick it up. Your little Pi and random-wire antenna are also producing quite a bit of energy at 176Mhz (maritime VHF ship-to-shore and stuff), 264MHz (military air-band, adjacent to a satellite-earth-station band), 352MHz (more military), 440MHz (amateur UHF), etc. All the way up.
This may be counterintuitive, but that's why radio is governed by regulations rather than YOLO, and why even unlicensed toy transmitters still have to comply with harmonic-content rules.
Filter your Pi to knock out all those harmonics, and the odds of the Coast Guard or Air Force knocking on your door will plummet.
(Also, I've measured the power coming out of one of these things, and if you can only pick it up ten feet away, either your antenna is total crap, your receiver is deaf as a post, or both. Even after applying proper filtering which eats some power, I was able to receive mine on a pocket radio out to about 200 feet, which surprised the heck out of me and I added lots more attenuation until my most sensitive receiver could no longer see it at the property line. It's a fantastic toy for exercising RDS/RBDS receiver and parser code, but it requires a little care and knowledge to use it responsibly.)
Anyone can learn this stuff, and everyone should, especially if they're going to put it on the air.
If the police come, I'll use the Constanza "Was that wrong?" defence.
Anyway, cool to see you hack this, maybe try to tweak the power levels a bit so the neighbors don't have a reason to talk about it.
-- The maximum power output of a personal FM transmitter allowed by the FCC is 250 microvolts per meter at a distance of 3 meters. The range of the transmitter depends on various factors such as terrain, obstructions, and interference.
Assuming ideal conditions, such as no obstructions or interference, the range of the transmitter can be calculated using the inverse square law. This law states that the strength of a signal decreases with the square of the distance from the source.
At a distance of 3 meters, the signal strength would be 250 microvolts per meter. At a distance of 6 meters, the signal strength would be 62.5 microvolts per meter (250/4). At a distance of 9 meters, the signal strength would be 27.8 microvolts per meter (250/9).
Typical car and household stereos have a sensitivity of about 2 microvolts per meter. Using this sensitivity value, we can calculate the range of the transmitter for these devices.
For a car stereo, the transmitter would have a range of about 26 meters (square root of 250/2). For a household stereo, the transmitter would have a range of about 63 meters (square root of 250/0.5).
However, in reality, the actual range of the transmitter may be shorter due to various factors such as interference and obstructions.
For the record I'm sure OP meant his has a range of 20 metres
Just kidding, I'm in the U.S. But more than a few times I have suddenly got Mexican musical content on my radio in the car when passing close to another car.
edit: Halfords still stocks these! https://www.halfords.com/technology/mobile-phone-accessories...
I guess I shouldn't be. Even letting them know you were fully aware you were breaking the law, most people would see its intended purpose -- to bring a little peace and comfort to a very old woman -- and have their own compassion kick in.
YMMV but I'm guessing you'd hear something along the lines of "Oh,... well,... (shuffles feet) ... just turn it off, then". Many of us have elderly people in our lives we wish we could provide some comfort to and most of us know we're headed there (if we're lucky to live that long). You know, assuming your 20m radius FM transmitter didn't, say, cause some cataclysmic event/knock emergency services offline for several city blocks, etc.
Put another way, while some police actually will pull you over and write you a ticket for going a couple of miles (km) per hour over the speed limit, most won't waste the brain power/physical energy/thermal paper to bother enforcing it.
This is in line with Peelian principles of policing. It was explained to me by a policeman and it was fascinating. He had worked in the UK, Australia and New Zealand.
In his view, Australia was considerably harsher in its policing and NZ was at the other end of the spectrum, UK in the middle.
I bought a house in my very early 20s. Roommates of mine finished the third floor with no permits. Went to sell the house ten years later and the location it was in required a U&O inspection. My realtor told me to lie, apply for a permit and pretend I just did the work.
Instead I called the local building inspector and said, “Hello my name is xxx and I’m calling to confess.” He cracked up laughing, came to the house immediately to look at everything and told me I was fine.
I suspect the OPs transmitter is hard to detect even at close (< 100 meters > 30 meters) range. Anything more powerful and you would definitely attract attention.
> Yes, *technically* it is illegal.
The law is an interesting beast. I know nothing about the law in India as it relates to FM band transmitters but I suspect that the law predates the common availability of adapters that one might use in ones car to add an input to a stereo that lacks such a highly technical circular hole for such purposes[0]. Once these devices gained wide adoption due to both their utility and -- more generally -- the fact that operating one is usually so benign that they can be difficult to discover let alone actually cause enough interference to warrant them to be seized.
The intention of the law was to prevent someone from operating a pirate radio station/give exclusivity to a single license-holder for that frequency. Since these devices don't violate the spirit of the law, the governing body finds it easier to carve out an informal exemption rather than explicitly write one in. It can also be tricky to correct a law that has a very valid reason for existing but may have cases where total enforcement isn't realistic[1].
The law may not have caught up to the reality on the ground and the legislatures answer to it is "enforce it when the interference is enough that someone notices." One might imagine a world where something akin to TV Detector-like Vans[2] drape the country-side in a dragnet to catch all of those pirate FM-input-devices but that usually only happens if there's a substantial amount of tax revenue to be gained ... to pay for the vans.
[0] I had one of these in the 90s (in the US, where it's not illegal if designed correctly) that connected my Discman to my ridiculously sad factory radio which lacked both external input and even a cassette deck.
[1] I do very little with regard to radio communication (if that isn't obvious) but I'd imagine most lawmakers do even less, so now you have to bring in experts to figure out "what's an acceptable amount of interference in this specific use case" and "how should a device like this be restricted." Not that government isn't famous for wildly wasting money or anything but I'd imagine the thinking is that it's not worth the effort to correct.
Heh. I drive a 2002 Chevy Suburban (don't laugh, I have a strong aversion to spending money on new vehicles) and it lacks an AUX input, so to this day I use one of those low-power FM transmitter adapters to pipe my phone's audio output to the vehicle stereo. They are amazingly handy little gadgets.
https://www.fcc.gov/media/radio/low-power-radio-general-info...
Looks like India doesn't permit it, but is looking at doing so (at least, for some purposes):
https://trai.gov.in/notifications/press-release/trai-release...
I wouldn't play at all with non-approved RF frequencies personally.
As someone who's worked in telecom for a number of years, the fines for broadcasting I've seen issued to individuals are insane. Not just radio but wireless amplification too. Different European country though.
Always check the legislation in the country of operation. Emergency frequencies are held sacred by the powers that be.
In germany its also legal to use plenty of bands in the RF Spectrcum with up to 750Watts (and potential more).
We are also allowed to do CB Funk in Channels 1-40 without anything and up to 80/85 (forgot details) when you register with Germany.
So your statement reads more like you are not allowed to do anything in germany. Its hard to believe to disturb stable systems just because someone is doing a little bit of FM on some known frequencies.
FM transmitting for private use is completely legal for UKW frequencies between 87.5 and 105 MHz and transmission powers lower than 50nW [1]. You can buy perfectly FM transmitters for your car, etch
[1] (German) https://www.autozeitung.de/fm-transmitter-bluetooth-nachrues...
[0]: https://de.wikipedia.org/wiki/Rettungsgasse?wprov=sfla1
Edit: “§ 97.403 Safety of life and protection of property. No provision of these rules prevents the use by an amateur station of any means of radio communication at its disposal to provide essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available.”
The built-in collection either didn't have songs that she liked (from the '40s), or they weren't clustered together, or were mixed up with other songs.
I could load a flash disk with her playlist to plug into that player, but it wouldn't know what to play at what time (calm songs in the early and late hours, peppier numbers on other days, festival specific numbers on some days). This was a big deal. I can even change the playlist from elsewhere (a script automatically mirrors the playlist that I maintain on a server)
Bluetooth streaming is possible with the device, but not an option for my MIL ... that would require her to learn to use a cellphone.
I haven't found the exact law in India, but looks like maybe it's legal for personal usage of FM provided power of transmitter is under 500 mW?
https://www.amazon.com/s?k=fm+transmitter&ref=nb_sb_noss
This is what he means, not some bigger pirate radio situation
Nowadays you don't even need that. You can turn the RPi itself into an FM transmitter. Search "how to FM broadcast on raspberry pi"
But yes, if you look at high-speed Pi GPIO with a Rigol it looks more like an EKG readout than the thing you might see on a logic analyser. Smoothing it enough to feed a line-amp is very lossy.
GPIO's usually looks quite squarey if you don't introduce parasitic reactances into the circuit with your test setup.
A spectrum analyser has probes!?!? This might be where I am going wrong... But the bench scope is largely in agreement about the distinct phases of a cycle at RF freq.
Never tried it, but given the way it works, you definitely need some output filtering unless you accept to pollute all harmonics of your channel (which might be licensed spectrum too, and interfere with services you don't want to interfere with in the first point)
I set this up for all my music in shuffle mode for my own radio-like always on streaming service via Tailscale.
There are lots of examples online of people doing this sort of thing. There's a simple example at https://github.com/pablodo/mpd_gpio/blob/master/main.py
Even a chapter of a book about it: https://link.springer.com/chapter/10.1007/978-1-4842-2406-9_... (I just found this, no idea if it's any good).
And also an IR version at https://www.ziemski.net/rcmpd/
[1] https://en.wikipedia.org/wiki/WFUV
[2] https://rivermontrecords.com/search?type=product&q=big+broad...
Sounds like you're about to start a Radio station for the nation.
Is this a quote / reference to something? If so, could you let us all in on what it's referring to?
You're invoking LLMs, but "benevolent AGI" was what got invoked originally. Don't conflate a hypothetical AGI with an existing LLM. Anything of the scale required to create a hypothetical AGI is going to be expensive. Period.
Is grandma really going to use a hypothetical AGI any better than she's able to use Spotify? Come on.
Unfortunately, the physics of this work out so that every playlist generated is composed of Nickelback and “Sweet Caroline” covers.
1. Never made it as a poor man
2. Never made it as a blind man stealing
3. This is how I remind you, that I’m really MOND.
Sometimes the answer is just staring you in the face. A Canadian face, that should have been from San Antonio, TX.
In a decade, it'll cost pennies a year.
Conversely, it wouldn't make a lot of sense to predict that it will always be as expensive as it is today.
Well, I guess "pennies" is a radical prediction. Cheap, anyway.
I'll give you an example: fabricating an ASIC is expensive. Using FPGAs is cheaper if the potential sales are low, but they're less performant.
If a hypothetical AGI a decade from now can do the radio gimmick, but it incurs an ongoing cost, but it's going to have wide appeal, it makes more sense to make a simple utility.
Better yet, the simple utility already exists and doesn't need a hypothetical "benevolent AGI". It doesn't even need an LLM. It's here today.
This entire sub-thread went off at a tangent of trying to shoehorn AI into somewhere it has no place being, just like the fetishizing of blockchain and attempting to shoehorn it into everywhere a database would be cheaper, more flexible and more performant.
A hypothetical "benevolent AGI" is going to be incredibly larger in scale than an LLM, thus much more expensive. You won't be running one on a laptop. We may not even have enough compute globally for a hypothetical "benevolent AGI".
Yes, let's make it so anything short of world-class creative talent (if that, even, if "AI" keeps advancing) is something that's of no monetary or social value, then wonder why people don't spend more time creating stuff. You're not motivated to play violin in your bedroom for nobody, or make paintings to hang in your own closet because nobody wants them? Or, there's no need for you to build this kind of great thing for your elderly relative because an AGI can do it instead? And now you're a couch potato struggling with depression and wondering what the point of living even is? Quelle surprise!
It's as if solipsistic intrinsic motivation is shit compared to having others want or need what you can do for them, and like maybe we need the latter in order to be healthy. But no, let's race toward further reducing our value to others as fast as we can, what could go wrong?
Just like there is no need to design and build the FM transmitter from scratch because [factory] can do it instead. Some of us still think it's fun to build things like that as a hobby, but those who don't can still have an FM transmitter to start with and create something more exciting from there.
How about a speech synthesis DJ, “that was Foo McBar from 19XX”?
* https://rancidbacon.gitlab.io/piper-tts-demos/#various_radio...
If the six speakers I selected for the demo don't match your taste in DJs, there's around 900 more in that voice model to try... :D
(The 3 audio players differ only in file format & whether I ran the output through normalization.)
Also, I was pretty impressed/surprised at the quality of their pronunciation of the meta-syntactic variables. :)
Might be cute to include some old original programming in your pirate radio!
https://archive.org/details/sherlock-holmes-1939-11-06-6-the...
She is fond of music from old classics (from the 60's and earlier), so I hooked up a Raspberry PI with an FM transmitter and created her own private radio station. She tells me what songs she likes and I create different playlists that get broadcast on her station. It preserves the surprise element of radio, and there is nothing in there she doesn't like.
The tiny FM transmitter is surprisingly powerful. Her neighbours (of similar vintage) are very happy too, so their requests have also started coming in :)
EDIT: I wanted to add that I am the UI ... she doesn't get to choose the playlist. To make my life easier, I just created different playlists for different times of the day ... calm/spiritual/slower numbers in the early and late hours, peppy during the late morning and evening etc.