First, the facts.
Both the FCC and ISED (Industry Canada) publish the regulations and technical specifications that unlicensed intentional radiators must adhere to. This is in the form of Part 15 in the U.S. and RSS210/BETS in Canada.
Most users of this equipment do not have the means to test for compliance. Therefore, both regulatory bodies require that all these devices must be certified, i.e., tested for compliance under a set of standard conditions in an accredited laboratory, before being either marketed or used. There is one exception in the U.S., which allows a small number of homemade devices (but Canada doesn't!).
Being compliant in the lab does not necessarily mean that the device is compliant in the real world. This is has been demonstrated with real world tests that have been conducted by one member of this site who owns the necessary test equipment.
The certification labs are climate and radio wave reflection controlled, do not use applied audio, tests are conducted at consistent heights, etc.; in essence, they just ensure that all these intentional radiators at least start out being compliant under identical conditions, particularly for FM.
In the real world, with audio (as opposed to dead carrier), it is highly unlikely that any certified transmitter is truly compliant, even those from reputable manufacturers. As soon as you add that audio cable and audio (if you're using FM), you're likely way over the field strength limit. In addition, the orientation of the antenna, antenna height and many other factors play large roles in determining field strength. This was also demonstrated in those transmitter tests by one of our site members.
In the case of AM, if you have any sort of elevated transmitter, and most do, for the transmitter to work at all it has to have a connection to ground, which violates the ground lead rule.
Now for the logic and educated guesses.
The FCC has to understand all these things. You're not going to duplicate laboratory results outside that laboratory. It's why, if you are ever visited by an FCC inspector, the first thing they do is to ask to see the certification label of the transmitter. That, at least, gives them a baseline that the transmitter was compliant under the controlled conditions of the lab.
An FCC (or ISED) inspector can shut down any radio station, which, in their judgement, is exhibiting bad behavior. But using a certified transmitter alleviates many of the issues such an inspector might have. Only if the transmitter has hugely excessive field strength, usually indicating modifications (and thus, voiding certification), will that inspector take action.
It's why driving around, looking for non compliant transmitters, is essentially meaningless. If these vigilantes are overly concerned about non compliance, they'd be better served lobbying the FCC to tighten up certification requirements, and to not just blindly accept certification results for transmitters that are dubious (such as those that have multiple power levels in the milliwatt or even watt level). They might also suggest that the FCC clean up at the laboratory level as well, if those guys are contributing to the problem. And if it's suspected that some certifications are bogus, lobby the FCC to remove them from their databases, and the devices from circulation.
Yes we should get along with other forums. But they talk but do nothing about it.
I actually got a music chain here in Canada to take a transmitter off the market that was misleadingly advertised as compliant with RSS-210.
Here's what I have found in actual use. Adding audio cables does add to field strength as you are adding more antenna. As Timinbovey saw in his tests. But the transmitter was intended to have audio cables. The testing just looks at the transmitter itself. I was at a lab here near Toronto and saw first hand at how the testing is done. So every certified transmitter is going to operate in the real world at above the legal limit.
The rules state carrier with no modulation in the test process as a carrier by itself is a stronger signal than when you add modulation and this can be seen on the spectrum analyzer. In other words in FM particularly you will get more range with a dead carrier than with audio applied. But no one is using a transmitter without audio. But the audio cables compensate for the loss when audio is applied and add more field strength than the modulation lessens it, depending on how you have the audio cables positioned and how long they are it can make a big difference. So it makes sense that there is adjustments made to compensate for the variables as Artisan pointed out in the real world when an agent is determining whether you are compliant. For AM also for the same reason compliance is done with no modulation. And also...output varies with frequency choice. That has to be considered also. Decade told me that the MS-100 is not power controlled over the band and compliance is taken at 98.5 center of the band so it's understood that frequencies above or below that can be over.
By the way I should point out that the Hamilton Rangemaster is certified but the user can adjust it to operate higher than the legal limit as it is adjustable and a little light tells you when it is 100mW as in the manual. But you never hear about that at the other forum. How did it get approval if the user in the instructions can up it to over legal limits?
Based on what I found out at my visit to the lab in November that would never get an approval today like that. At least here in Canada.
Here's the page in the Rangemaster manual that shows the user has a power control and can with a control increase the power over legal limits.
https://www.manualslib.com/manual/138104/Hamilton-Hamilton-Am1000.html?page=13#manual
I have nothing new to say about the SnobbyHobby boys at their 'Home of the Transmitter Challenge". As has been said: There is a grammar stumble when calling "measurements" a "challenge". Finding a hair-width of difference between one compliant transmitter and another is more of a 'head challenge"; "did your mother drop you on your head?"
But when it comes to nit-picking, I wonder how many more inches of range can be squeezed out of a 12-foot AM antenna as compared with the more literal 3-meter (10-footer). Probably 2 or 3 inches. A small advance into an empty yard with no radios, unless you are near a homeless tent-camp.
I view the FCC Part 15 rules as 'ballpark' estimates; plus-or-minus tiny numbers; itsy-bitsy distances. If you want to be "caught" and "investigated" you've got to really try to annoy a thin-skinned upholder of neighborhood standards.