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Contrary to what some would have you believe, there is no requirement, at least in the U.S., for a Part 15 broadcaster to use a Part 15 certified transmitter. You must, however, use a transmitter that is compliant with the Part 15 rules (15.209, 219, 239).
This topic tends to become a hot button when considering Part 15 FM, mostly due to anti-FM bias. 15.239 states that a compliant FM transmitter must have a maximum field strength of 250uv/m at 3 meters. There are other technical considerations as well, but that is the main one from a rule (and FCC) perspective. And it is very difficult to measure field strength without expensive test equipment. That is why the FCC published a technical bulletin, which suggested that a compliant Part 15 FM transmitter should have a range of no more than 200 feet to a typical receiver.
Exactly what a typical receiver is is of course open to debate, and the FCC didn’t define it. Ancedotal evidence from the field suggests that you’ll get up to 200 feet range to a portable with decent sensivity (around 4-5uv), and more to good car radios (which typically have sensitivity in the 1uv range or better), from a Part 15 compliant FM transmitter. Those ranges, of course, are also dependent on a number of other factors, such as antenna height, obstructions, RFI, weather, etc., and could be much less. Those signals, particularly in the case of listening in a car, would be awfully weak at the upper ends, and subject to dropouts and other interference.
So don’t let anyone tell you you’re a pirate if you’re getting that kind of range from a non certified FM transmitter. Whether you consider a range of 200 feet or so useful or not, of course, is dependent on what you’re trying to do.
The legal landscape is much different in Canada, and other countries as well, where ALL transmitting equipment needs to be certified for its intend use. BETS-1 is Canada’s equivalent to Part 15.239 and is intended for broadcasting; RSS210 is intended for non broadcasting uses. In some countries, such as the UK, you require a license for any kind of transmitting, micro powered or otherwise.
Understood
But as Artisan Radio points out, not everyone understands the situation.
A good set of rules would follow a consistent pattern of writing, so we can reasonably guess that entirely different people wrote the inconsistent AM FM sections of Part 15.
The portion about AM transmitters takes into account that home hobbyists might not be either technically adept or equipped with laboratory grade equipment.
The section on FM speaks only to the trained technician and cannot be satisfied without lab gear.
As mentioned, the Commission compensated for the imbalance of style in their published rules by issuing the field paper estimating 200-feet as the expected range for FM.
“Intentional Radiators,” otherwise known as micro-transmitters, can be an exact science or an inexact one, depending.
That would mean that in Canada the only certified AM transmitter (Procaster), is certified under RSS-210 not BETS-1 but the certification is the 100mW, 3 meter antenna and ground rule. So setting it up outdoors as per instructions and certification, it’s still not a “broadcast transmitter” so the really grey area here is how could you do the outdoor set up and say you are not broadcasting? As soon as you have the antenna mounted in an outdoor location and the signal will get to the general public, you are broadcasting.
Why doesn’t Procaster know this and just get it BETS certified?
The rule for BETS-1 which is for broadcasting transmitters isn’t different for AM or FM, if you are broadcasting, it has to be under BETS-1 as a broadcast transmitter.
I agree Mark.
And I know of at least one person who has had issues with Industry Canada because they were doing broadcasting (as Industry Canada and the CRTC defines it) with an RSS210 transmitter that wasn’t BETS certified (not me, by the way). That individual pointed out the same issue, and the Industry Canada agent stood down, but there’s no guarantee that that will happen everywhere.
There are no AM BETS certified transmitters. The only RSS210 certified transmitters I know of are the Talking Sign TS-100, and the Procaster.
On FM, I use a BETS certified Decade CM-10, and an RSS210 certified Landmark FM350. I’ve used BETS certified Decade MS-100’s in the past.
One of the issues with a BETS certified AM transmitter is that the maximum field strength is 250uv/m at 30 meters. If you classify a ‘good’ AM signal at 100uv/m, that would restrict range to slightly more than 60 meters or about 200+ feet.
Artisan is correct. In the USA you are not required to use a certified transmitter, but must operate whatever you transmit with within the rules.
However, to SELL a transmitter it must be certified. That’s sell as a business, not just a guy selling one unit to another. But to manufacture and sell as a business completed transmitters, they must be certified.
As you mentioned, it is difficult for the average person who is not an engineer and who does not have access to the equipment, to determine if their transmitter meets the rules (especially on FM) so it’s not a bad idea to buy a certified unit. On AM with a smudge of knowledge, a decent VOM and a ruler you can figure out if you meet the rules. Not so with FM.
The discussion on legal FM range will rage on forever, I suspect. However, 250 uVm at 3 meters is a given figure. This amount of power can only go so far. There are no conditions that will suddenly give you 2 blocks or more on FM with that power.
Determining realistic FM range is doable. Now I can’t remember? Did I test this? I tested a bunch of FM transmitters a couple years ago, determined that nearly every one sold as certified was well over the legal limit except, if I remember right, the C. Crane which was well under. But it was also (somewhat secretly) easy to adjust the power output, IF you have means to measure.
Perhaps this might be an idea for a good test in my wide open nearly mile long test field. (I swear I did something like this). I could measure field strength and set a C. Crane to exactly 250 uV/m at 3 meters and simply walk away with a radio to see where it dies. Of course, this test would depend on the sensitivity of the radio so it’s not really a valid range test, except to that one particular radio, but I could take FS readings as well. I remember doing something like this — I’ll have to check my old tests. But you’re not going to get even a block with a legal transmitter out in the open field, and much less where there are houses.
Many MANY places advertise their transmitters are “compliant” which sort of hints that they’re legal. But being compliant does NOT make it legal to sell them in the USA. And as I discovered claiming to be either compliant or certified also does not mean that the transmitter one buys is legal.
A lot of folks buy a certified FM transmitter and are pleased with their range — several blocks, even half a mile, and they get all excited about what a “legal” transmitter can do. Trouble is, they’re NOT legal. Now, how that happens I don’t know. Do they submit models with the output lowered to get certified then sell them with higher output on purpose? Or by accident? Or what? We’ll never know. Then of course there are those sold as certified that are not, and the certification numbers are bogus.
Can’t help with anything that has to do with Canada, however. I dug out the links to my FM transmitter tests if you’d like to see how illegal many certified transmitters are.:
http://www.ironrangecountry.com/fmfieldtests.pdf
http://www.ironrangecountry.com/failsafetransmitter.pdf
http://www.ironrangecountry.com/edmreview.pdf
http://www.ironrangecountry.com/edmantenna.pdf
http://www.ironrangecountry.com/broadcastvisiontest.pdf
These tests should give you some idea as to the legality of certified transmitters for FM!
Tim in Bovey
Tim’s FM Tests
I printed copies of all Tim’s FM tests for my engineering files, they are extremely helpful.
In fact I immediately purchased an EDM Mono FM Transmitter based on Tim’s test even though he disclosed it is NOT certified. But it is well priced and extremely good quality.
Therefore when I use it the responsibility is all mine.
In reply to artisan I’m considering getting the Talking sign from part 15 engineer as it’s certified for Canada just to have an AM transmitter on hand. By the way RSS-210 gives you a choice between the 100mW and 3 meter antenna and ground or the 250uV/M @30 meters with nothing about transmitter power or antenna length….an advantage is you can have any antenna and put the transmitter where you want.
I’n still considering because I’m figuring out if I could use it.
After all it is a “talking sign” isn’t it? Wasn’t it meant for “broadcasting” to an area so the public can tune in to hear the details of your house? The general public?
Opinions?
I don’t think you’ll have issues with the talking sign in Canada as 250 uVm @ 30 meters is far more tha our 15:209 rule allows so we use 15:219
that said you could rent or buy an FIM like the Potomac FIM 41 and you would know. I’ll bet you could do 1.5-2 miles no issue and with a longer ground lead I know it should be no issue as long as you check the field strength.
Let us know your results.
Yes you are right but it’s the broadcasting/non broadcasting thing that’s the question.
Am thinking still…..just to have an AM transmitter on hand. Don’t have transmitter yet.
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