I think the orginal intent was to protect TV Channel 6 from "buckshot" from FM transmitters operating in 88.1. As one can see from the FCC website, locations of 88.1 stations have to take into consideration TV Channel 6. Now that being said, Channel 6 for the most part is gone. I know here in my location we used to be able to hear Channel 6 from Orlando but no more. And surprise surprise surprise, I now can hear a God, Guns, and Guts station in central Pasco County.
From Florida Low Power Site:"87.9 MHz (LPR) unidentified, Land O Lakes/San Antonio area; confirmed still active in May, 2014 by J. Mouw. First noted by the editor in May 2013, first appearing on SR-52 eastbound, peaking around the Ehren Cutoff Road (about mid-way between US-41 and I-75), but never a great signal, and suspect this is either north or south of approximately this location which is mostly cattle ranch land. This one is “new” having never been reported by anyone I’m aware of. Format – today at least – was satellite-fed Republic Broadcasting Network, with paranoid/conspiracy “patriot” talk show, a break at the bottom of the hour with network spots for campingsurvival-dot-com and a company selling “survival seeds” to grow post-Holocaust."
Give your radio dial a look while driving around. You WILL be amazed at what you might hear on this frequency. And remember folks, 87.9 IS FM Channel 200!
Think this is certified?
To clarify the above post: For unlicensed intentional radiation under Part 15.239, 250 uV/m @ 3m, 87.7 and 87.9 are not allowed. If someone were to operate a transmitter on 87.7 or 87.9 because they think they are covered by 15.239 they would be breaking the law and subject to a NOUO.
I have seen transmitters with a FCC licensed sticker that work on 87.7 or 87.9. A sticker is cheap. If the sticker is printed in China, the people printing it probably don’t know what it means. If the sticker is put on a transmitter made in China, the people putting the sticker on the transmitter probably don’t know or don’t care they are misleading American consumers. Just because it is possible to buy transmitters that say they are part 15 compliant that work on 87.7 or 87.9 does not mean they are actually part 15 compliant.
There are quite a few Full Power Digital TV stations on VHF channel 6, 82-88 MHz. There are bunches of digital low power digital TV stations on channel 6. There are quite a few analog low power stations on channel 6. There are even some translators on channel 6. Anything licensed by the FCC is a primary user of the channel. http://transition.fcc.gov/fcc-bin/tvq?state=&call=&arn=&city=&chan=06&cha2=06&serv=&type=0&facid=&asrn=&list=1&dist=&dlat2=&mlat2=&slat2=&dlon2=&mlon2=&slon2=&size=9 Part 15 devices must not cause interference to licensed users and they must accept interference from licensed users.
So unless you want to get a NOUO, don’t use 87.7 or 87.9. It may be possible to use a wireless microphone in channel 6, but you need to be 80 miles from any CH6 broadcasters (unless you are in zone 1, in which case you need to be 65 miles from any CH6 broadcasters).
Now, if you want to drive around listening to 87.7, the audio from analog channel 6’s, there is stuff to be heard. In DC, there is a Spanish station on 87.7. On the eastern shore of MD, there is a Christian station on 87.7. http://transition.fcc.gov/fcc-bin/tvq?state=&call=&arn=&city=&chan=06&cha2=06&serv=TX&type=0&facid=&asrn=&list=1&dist=&dlat2=&mlat2=&slat2=&dlon2=&mlon2=&slon2=&size=9
Anything you hear on 87.9 is a pirate, unless you are in the bay area, CA or Reno, NV. http://transition.fcc.gov/fcc-bin/fmq?state=&call=&city=&arn=&serv=&vac=&freq=87.9&fre2=87.9&facid=&asrn=&class=&dkt=&list=0&dist=&dlat2=&mlat2=&slat2=&NS=N&dlon2=&mlon2=&slon2=&EW=W&size=9
Another problem with 87.9 is if there is a HD station on 88.1, the lower HD sideband will make a mess of 87.9. The HD 88.1 doesn’t even need to be close to you, as a noise source HD sidebands carry quite well. It can be below the point of being decodable by a HD radio and still be noise for an analog source.
The datasheet for the transmitter in John's link boasts a frequency response of 20 Hz to 20 kHz. I suppose they don't know or care about the 19 kHz pilot when they make these things up.
Neil
I've seen these transmitters too, at dollar and hardware stores and at a flea market once. They were all different brands, and made to get the sound of your mp3s to the car radio. One even takes a USB stick drive and plays the files on it, which gave me the idea for the ultimate tiny radio station that needs no mp3 player or computer to run.
I noticed two types of these transmitters, one that got to every FM frequency and one with about 6 channels on the bottom, and 6 on the top of the band. The 12 channel ones the same lineup on every transmitter, so they might all use the same chipset.
It might be misleading to say it's FCC Approved to engineers like you guys but I doubt buyers or the stores themselves even know, they probably just buy 'em off the truck. In reviews on line, some even like the out of band tuning, because none of the licensed channels in their area are free. Could the FCC let them slide because it keeps the transmitters away from bumping into licensed stations?
20-20 khz, that might be the response of the preamp, not the transmitter part, that's what I thought. My own Professional Transmitter was listed in some ads as "100-15 Khz" when it clearly has more bass than that. It is kind of low on the subbass, but I think it's hitting at least 50, and still sounds 100 times better than any licensed station on my radio!
I just took a look at the The Golden Ram transmitter, and that looks like the same thing that was in a Target blowout sale after xmas a few years ago, they had these in white and red boxes for a few dollars. I remember it because of the egg shape and temperature display.
Because I was in Part15 radio, a friend of mine got the Target transmitter and since the audio cable is an antenna, added a 6 foot audio extension cable to the player and stretched it out. Let's just say it did well for a tiny transmitter.... The output power on these things is all over the place, some have trouble getting 6 feet to a car antenna with a hissing signal, others can reach a friend's car when you're driving a convoy.
The datasheet for the transmitter in John's link boasts a frequency response of 20 Hz to 20 kHz. I suppose they don't know or care about the 19 kHz pilot when they make these things up.
Yes, that jumped right out to me as well. The audio must be screeching when highs are over 15KHZ.