This looks interesting, but it's also a confusing listing, the title says:
0.5W FM Transmitter Stereo 88M-108MHz Campus Radio Broadcast Station Receiver
https://www.ebay.com/itm/256320142096
So why it say "receiver at all? Anyway the description clearly says it's a transmitter:
Version: V100
Output frequency: 88-108MHz100KHz step(320 frequency transmissions)
Display mode: LCD display, the display content is the current transmitting frequency
Output power: 500mW (0.5W)
Supply voltage: 5VUSB-type-C
They're $35.99 with $14 shipping. I'm not looking for a part 15 FM transmitter, but I'm still curious what I'm looking at...
You are looking at another Chinese illegal cheap transmitter. And on the same Ebay listing as this it shows related items. A 25 watter that is only $95.00
https://www.ebay.com/itm/235694536782?_trkparms=itmf%3D1%26aid%3D1110006%26rkt%3D4%26asc%3D20231107084023%26mech%3D1%26algv%3DSimVIDwebV4WithCtxRankerV1UnifiedFeaturesV2%26pmt%3D1%26amclksrc%3DITM%26sd%3D256320142096%26sid%3DAQAKAAAAEAGjZsAmDOwkX2se35Wao9A%3D%26itm%3D235694536782%26noa%3D0%26plcampt%3D0%3A13729529012%26algo%3DHOMESPLICE.SIM%26ao%3D1%26rk%3D2%26pid%3D101875%26b%3D1%26mehot%3Dnone%26lsid%3D0%26meid%3D7b345fbc529b4a27acbd623cb7923f11%26pg%3D2332490&_trksid=p2332490.c101875.m1851&itmprp=cksum%3A2356945367827b345fbc529b4a27acbd623cb7923f11%7Cenc%3AAQAKAAABEJbOa4aZh83HAIOb9NKIclsNhJn%252F4s4LXfNtXkjfwm9ASZvqKo92rhjh8S89vOM7RPm3bMgZQU2wL3m%252BgnVCOrdw%252FsQXcygIFdNqWjEl5BZzaMaFP8YgReWJ6DMOb4C09h3VzWK0tKLbfcjKlBwsy08onwDYy0KyEj4vjWA0zU0waN8BZ2xfnxrFw%252Ft0HdT3K9h7RbrEiRUxSYyKs%252BsQx1WXWKkDG%252F4FNf%252FbWff3O%252B8LtfgGkRgRhaj1xrNBUa66B94ZeVFXk05OR9hCO9ksiVAPTE5ZTANBzxWiGK%252Bw0Otu%252BhMp7HlrJOTB0p%252FdB8EZm%252BXEBy2EwKEOWE%252FT%252Fmb23tal3SmqXdwKFKZG%252BP4HVzDl%7Campid%3APL_CLK%7Cclp%3A2332490
This is the reason that Gerry at Procaster hasn't in almost a year sold one of his new FMs.
Because everyone sees this, doesn't care about legal or not, it's cheap, and lots are being sold as we speak. And Gerry goes through all the red tape of getting it certified spending time and money doing it properly, $1000s with lab fees and people see this and say why should I spend hundreds$$$ when I can get this for $35, and stick up any antenna I want.
And for 35 bucks I get a transmitter that goes 1500 meters(close to a mile)!
Here's another a bit like the one you posted for even less.....If I was a manufacturer I would see what I am up against and would never bother except to make one for my own use. Legally?, no way I would sell any. As Gerry is finding out.
@mark It's powered by USB-type-C, like a phone, 5 volts. It's output power is 500mW max. It definitely is as compliant part 15 as anything else. No, it's not certified, and yes it Chinese or Japanese or whatever, but it's legal for operation in the U.S.
I'm curious why they describe it as a Campus Radio Broadcast Transmitter.
Took a look around, a couple bucks less on Amazon, skimmed through about 20 reviews there, most positive, primary complaints are it's tiny and delicate, has no instructions, and its not enclosed on the sides. Some bought multiple units, it's interesting reading how they were using them. One guy with a jukebox, another used multiple for a "Sonos" type setup (whatever that is), and another on his boat.. but I didn't quite get how, and others, they're apparently popular but didn't see any comments about hobby radio station broadcasting (nor campus).
This is the reason that Gerry at Procaster hasn't in almost a year sold one of his new FMs.
Feel for him, but like I asked before, who'd he expect to be his market? Presumably, since he's in Canada, he expected Canadians, and certification is a requirement there. In the U.S. compliance is all that's required, so a $35 xmtr is fine.
Of course I know you know that, but just saying.
@richpowers No he expects as with the procaster AM most of his business in the USA
As for legal yeah I guess if you could turn it down to half a block instead of the claimed km and a half range(1500 meters) you could get away with it. And 35 dollars is better than spending several hundred dollars to go that same half a block.....I see what you are saying, that it can be operated legally if you can attenuate the power enough. Question is, would anyone use this "legally"?
Mark, with the transmitter I linked and pictured, it's pretty unlikely that "attenuating the power" would be of any concern to insure it's legality. -- or rather so it seems to me. Again, it's power source is a measly USB delivered 5 volts and it's max output is 500mw! So there's nothing to attune. This one is a different creature than some of those 25 watt or whatever transmitters your referring to.
It doesn't appear this transmitter would even be capable of performing beyond part 15 limits
Putting it visually in perspective:
Size:80*48*8mm - That's roughly 3 inches x 2 inches and less than a half inch thick, so this transmitter is about the size of a matchbook.
500mw is waaaaaay over the limit for Part 15 FM. To give you some perspective, the maximum legal power would be well under 100 NANOwatts with a resonant antenna.
In Canada, it says right in the BETS rules that the expected power output for a compliant transmitter is about a MICROwatt or so. And Canada allows much more field strength than the U.S.
In New Zealand , where the allowed output is 1 watt, range (as communicated by Johny C a while ago, can be as much as 20km (line of sight), that's over 10 miles! Usually much less than that due to obstructions but still multiple miles.
When they say 1500 meters, they're really underestimating (to make the transmitter appear at least somewhat legal).
And when you're dealing with that much power, any spurs and harmonics (which I'm sure exist at that price point) would cause a lot of interference.
The supply voltage it runs on has nothing to do with it. This is no different than the other 500mW CZH 05B transmitters. 1/2 a watt is 1/2 a watt and with and a telescoping antenna that can be swapped for double the length. To put things in perspective with chips available now the whole transmitter can be on a chip that is 5*5 millimeters! and then the amplifier.
Another chip for the display and PLL for frequency.
Your phone can transmit miles if it has to to reach a receiver tower that is not near and it works on a 3.7 volt lithium battery and would just be a tiny chip as this transmitter. The whole transmitter and amplifier in the Procaster FM take up about a centimeter of space! Two tiny chips can replace the whole circuit board of conventional through hole components that make up the Decade MS-100 that is 6x9 inches! And the chips may I add work on 5 volts whether the actual supply is 12 volts. I don't think you realize how much 1/2 a watt is.
Yes you are correct that in the USA you just have to be compliant but this is not even close and is bordering on encouraging illegal operation.
@artisan-radio Johny C in New Zealand is using an outdoor(I forget what kind) antenna up on a pole or the roof of the house as the one watt can be used with any antenna and no field strength involved. That's how he is getting the 10 miles.
Ok. Guess I shouldn't have said anything - I really don't know part 15 FM issues at all, have no experience or interest in it really, but do know it's not governed by power limits like AM is. So while 100mw can prove quite effective in AM frequencies, I guess I just presumed a max 500mw output in FM frequencies couldn't amount to much and that an FM transmitter about the size of my cigarette lighter and powered by a few AA batteries could possibly produce much output...
Apparently my perceptions of part 15 FM are way off. But these transmitters being so incredibly tiny that I just have a hard time believing they could be capable of exceeding the part 15 field strength limits. So much for perceptions.
Anyway, if that particular eBay seller hadn't specifically referred to it as a "Campus Transmitter" we wouldn't even be having this discussion! That's really the only thing that prompted me to post about them.
I stand corrected about it probably being a compliant part 15 FM transmitter.
@richpowers No problem! 500mW and a telescoping antenna length 1/4 wave length with FM can get you farther than you get with AM! Johnny C in New Zealand gets as mentioned 10 miles with 1000mW(1 watt).