That article seems to be intended to get broadcast engineers reporting on potentially illegal Part 15 broadcasters. It contains little for newbies to Part 15, and what it does contain is potentially misleading.
Range is not a suitable indicator for legality of a Part 15 FM signal. Range is almost entirely dependent on the receiving system, including the sensitivity and selectivity of the receiving radio, as well as the efficiency of the antenna. To a lesser extent it also depends on where the receiving system is located vs the transmitter (i.e., obstructions can greatly affect range).
You’re going to get a lot more range with a car radio of, say, 0.5uv sensivity, and a tuned whip antenna, as opposed to the run of the mill OEM crappy car radios, and those stubby roof antennas, and even more from a typical portable radio. You’ll also get significantly more range line of sight to the transmitter.
Certification was created specifically because most Part 15 broadcasters, AM and/or FM, don’t own the appropriate test equipment to determine whether or not their transmitters meet the field strength and other requirements. If you use an *unmodified* certified transmitter, then you can be as certain as you can be about anything in this life that you won’t run into significant issues with the FCC. Regardless of the range ‘experts’ feel you should be achieving.
I’ve gotten less than 200 feet range to a lousy receiving system (a portable radio) using a Canadian BETS-certified transmitter (the Decade MS-100 – and BETS allows 4 times the field strength than Part 15 on FM). With that same transmitter, in the same location and an excellent receiving system (sensitive car radio, whip antenna) I was able to listen to it well over 1/2 km. Some cars with different radios and antennas faded away at 100-150 meters. Again, with the same transmitter, same location.
Now, one of the arguments I’ve seen is that adding cables to an FM transmitter will increase field strength to possibly illegal levels. That may be, but the FCC isn’t comprised of dummies, and they must recognize that as well. It doesn’t take away from the fact that the transmitter is certified in a special laboratory, and deemed usable for the general public without test equipment. If you’re going to use it, you have to get power and audio to it somehow.
I find it interesting that the people that look at Part 15 FM through a microscope ignore the same obvious issues with Part 15 AM. Possibly because they run AM transmitters.
Many people get around the Part 15 3 meter AM antenna rule by elevating their transmitter, and not attaching a ground lead. Some report ranges of well over a mile with these kinds of setups, even to portable radios.
For an AM transmitter to work at all, never mind for any significant range, it has to have a ground. Something else must be being used as that ground, and it’s likely it’s the power and/or audio cables feeding the antenna. That fact tends to be ignored, particularly if the transmitter itself is certified.
The situation is exactly the same as with Part 15 FM. And just as with Part 15 FM, I’m sure that the FCC is aware of it, and takes it into consideration in the certification process.
I beieve that if the transmitter is certified, and not modified in any way shape or form, then it should be OK to use. At the very least, it demonstrates that you are attempting to abide by the rules, and not just a blatant pirate.
On a side note, both e-bay and Amazon are tightening up on allowing non certified transmitters to be sold on those venues. I’ve seen listings disappear from e-bay and Amazon on a reguar basis.
And not all those Chinese transmitters are illegal. According to RECNET, and confirmed on both the FCC and Industry Canada equipment databases, the CZE-7C and its variants have been Part 15 certified. If you look up the Signstek ST-7C on Amazon, the FCC and/or Industry Canada certification numbers can be found on the case of the transmitter.
To be sure, you can still purchase non certified, illegal transmitters. But things are getting better, and some of the manufacturers are at least making an effort to get that certification.