Reading through the published PDF for the specs on the AMT 5K unit, it all looks great! However something in there made the hair stand on the back of my neck.
The RF power adjustment to "compensate" for antenna system losses.
Now before anyone gets their socks in a wad over what I am about to say/ask...me personally I think having this ability to adjust the final RF stage level to compensate is great..but that is my personal prospective.
However, an inspecting FCC agent might find that feature not so great. Some would argue that a certified unit also has this power adjustment feature (older versions). Very true, those do have the power adjustment. From what I understand, the newer versions do not.
As the AMT 5K is a kit, perhaps there is nothing to worry about. Then I pour over the Part 15 regulations and still cannot find any provision anywhere to allow for even a slight power adjustment of the final RF stage to compensate for antenna system losses, which btw, is inherent with a 3 meter long stick sporting a loading coil or other tuning/matching network.
So I guess the big question is this...is it safe to assume that running any Part 15 transmitter under the 219 rules above the 100mW final RF stage limit in order to compensate for antenna system losses (inherent) is "A-OK" with respect to those limits defined in the rules?
Again, to me I think it should not be any big deal as long as the power level is not so ridiculously high...say a 10 to 20 percent +/- window or so.
The second part to the big question would be has anyone with just such a transmitter, carrying a certification number or not, and the power level adjusted above the 100mW legal limit ever been inspected and passed with flying colors?
Or...has that yet to happen?
I do not wish to discourage anyone from using the AMT 5K or any other unit capable of power level adjustment above 100mW, but I believe this issue to be one that does merit attention and perhaps even clarification before someone out there ends up having a bad day.
Again I refer to the rules and the fact there is no provision for adjusting the final RF stage above the 100mW legal limit.
Now some gripe and moan about the Ramsey AM 25 and its ability to operate above 100mW...as much as up to 1 watt in some cases. And I have read over and over about how no one would buy such a unit simply because it can be operated at that higher power level. Well it will ONLY operate at that higher power level if you set it to run at that higher power level, yet there is still that attitude by some about tossing that unit aside because "it can" operate above that legal limit.
Where is that attitude for other transmitters capable of operating above that legal limit then?
Can't have it both ways or put special preference and dismissal from one unit to another when it comes to being legal IMO.
Also this point...unless you have an accurate field strength meter such as that Potomac the FCC field agents use, how is a user going to determine what power setting point to stop at to meet that expected field strength reading when compensating for antenna system losses?
I suppose we can all sit back and let it slide for now..and hope nothing comes of it.
RFB
The ability to "fine adjust" the input to the final is not forbidden in the language of Part 15, in fact the "responsibility" to make that adjustment is implied in the language.
The rules require the transmitter operator to apply no more than 100mW to the input of the final. Therefore going above 100mW is NOT allowed. But there are situations where meter readings will disclose that the final is being driven by LESS than 100mW. One of my transmitters comes to 90mW to the final. Therefore, although I am not obligated to get that power up to 100mW, I certainly have the privilege of doing so, for which a built-in adjustment would be much more convenient than soldering new parts through experimentation.
If being able to go ABOVE 100mW to the final seems like a taboo, it only becomes a taboo if cheating takes place. The rules clearly place the obligation on the equipment operator, who, if he was determined to boost power, could change some parts and add a stage.
It's like keeping the car at the speed limit. The fact that the car is able to exceed the speed limit is not an infraction of the law within itself.
"The ability to "fine adjust" the input to the final is not forbidden in the language of Part 15, in fact the "responsibility" to make that adjustment is implied in the language."
Indeed there is no "language" stating one cannot adjust the final power. But the "language" does state what that power limit is does it not?
Riding the fence is not a position the FCC takes.
"But there are situations where meter readings will disclose that the final is being driven by LESS than 100mW. One of my transmitters comes to 90mW to the final. Therefore, although I am not obligated to get that power up to 100mW, I certainly have the privilege of doing so, for which a built-in adjustment would be much more convenient than soldering new parts through experimentation."
In this case Carl, it is a completely different scenario. 100mW as we know is the absolute limit per the "language" of the rules. Therefore if your unit is running at 90mW, you can safely presume that you can adjust that to run at the maximum 100mW allowed..per the "language" of the rules...but beyond that...well what does the "language" of the rules say?
Nothing in fact. But what "language" will be applied at this point when your inspecting agent finds your above the 100mW limit? Someone will be singing a tune of "NOUO" top 40 hit.
"If being able to go ABOVE 100mW to the final seems like a taboo, it only becomes a taboo if cheating takes place. The rules clearly place the obligation on the equipment operator, who, if he was determined to boost power, could change some parts and add a stage."
Ok..so where is the line drawn at in relation to "cheating"? The "language" in the rules say nothing about adding another stage or booster. Yes its up to the operator to adhere to the rules. Now..does the rules "language" allow for a power adjustment? Nope. Nor does the rules say a transmitter for 15.219 cannot have a power adjustment.
So..with that in mind..is it safe to say that the responsibility not only lies on the end user, but also the kit maker as well? Why would a Part 15.219 transmitter need a power adjustment when the antenna systems being connected to it is INHERENTLY lossy to begin with? Or would this fall into the category of "Your on your own Jack".
Again I ask..has any station out there running a Part 15.219 transmitter with the ability to adjust that final RF stage and running above 100mW to compensate for inherent antenna losses ever passed an inspection?
Our (us out here) interpretation of the "language" of the rules may not be the correct interpretation. That is my whole point. At what point will this point I am making become valid enough for people to start putting away this "political correctness" attitudes?...when a station, possibly a member of this forum, gets tagged with a NOUO??? Will this issue then become a matter of importance?
Who will be the first to step up to the plate and test that "language" when the field agent is standing there taking measurements?
The rules are the rules. There is no "middle area". If we are to promote being legal, does that also get thrown into a middle area because of varying "language" interpretation??
Boy talk about causing confusion to a poor someone out there new to Part 15 radio reading all this!!
Now just because the car can go 180MPH and the speed limit sign says 70, does that change any of the road rule "language" of adhering to the 70MPH speed limit?
I don't think so. That state trooper is gonna nail you because you DID exceed that posted speed limit. The law does not care that your car can go 180MPH, or that you can push harder on the gas pedal. What the law cares about is you going faster than the posted speed limit.
Isn't it safe to say that the same would apply to the laws in Part 15.219 regarding the speed limit set on the grand highway of license free radio airwaves??
The law is not going to care that your Part 15 transmitter can be adjusted above the 100mW rule. They will care when they "radar/laser/clock" your signal as being above that established speed limit...yes???
YES!!
THAT is my point!
Isn't it better to compensate for an antenna system which has inherent losses by working with the antenna system itself, which is where the problem is anyway..instead of taking the (in my opinion) "cheating" way via a power increase??
As I stated, me personally I see no reason why there should not be a provision in there for allowance to have a little bit of wiggle room. But I know for a fact that the FCC's prospective is this. When that wiggle room allowance becomes not enough wiggle room, that opens up a can of worms for even more wiggle room, and even more potential for interference.
Given the fact that an increase in power to the main carrier will also increase the level of the unit's harmonics, a filter put into a transmitter meant to filter harmonics by at least 20db from a mean power level of 100mW will not be effective if that mean power level is increased. It would require a better filter for the higher power level to make those harmonics meet that 20db in band harmonic rejection requirement, as well as meeting the harmonic rejection minimums for out of band stuff.
A whole new can of worms alright.
Given the fact that not every installation will be the same, how is the standard going to be established for this power adjustment provision with the vast variety of environment conditions, antenna system design and implementation, and other factors?
Now throw in the fact that MOST Part 15 operations cannot afford a Potomac or even a used fancy Motorola RD2012 analyzer to make proper measurements. We can get close with approximation with the use of a typical field strength meter, or just a plain old radio and listen for a fade out point at some distance. Granted that shows the attempt to comply with the rules...ahh the rules...again it says 100mW.
I think it is a very tricky and very dangerous path to be walking on..taking chances and praying that the 110mW power setting or more will not be any issue to an inspecting field agent because of an attempt to compensate for an inherently lossy antenna system.
I examine all angles when it comes to those rules and license free broadcasting. I never take the grey blindfolded fly by luck approach. But that is just me.
With all due respect to the maker, and to everyone here, I find this bleh approach and semi-quasi adherence to the rules as taking a big risk which no matter what "language" path you want to take, are quite clear and requires no slide rule to understand what they say and mean.
Fair warning is what I toss out here. Indeed....its up to the end user to comply.
And I wish all the best of success to the new AMT 5K! I may just get one myself just to say I have one. Maybe see how well it works going into a TCU-30 coupler. Which btw, hooking that AMT 5K up to a CC system, then it wont matter if the TX has a power level adjustment feature! 🙂
RFB
It is interesting to compare technical language with legal language.
Technical language is based on total precision, being very precise in stating even the smallest pertinent facts, down to the size of washers and the color of a wire.
Legal language is something else. It is "codified," put in code familiar mostly to attorneys with four years of law school. With law we hear people say, "If it isn't specifically banned then it's o.k." But a lawyer might not agree; or a court might overrule the lawyer.
RFB is right in cautioning against that final acid test of getting a NOUO, which, to be fair, is contestable, if we have $24k to take it to court with the burden of proof being ours.
And with that dark shadow of violation always in the air, we need also to worry if we are entirely compliant. The installation that meets the closest micro-meter measurement of compliance could be hit with a NOUO.
Using the airwaves is dangerous.
Driving on roadways is dangerous.
Deep sea diving is dangerous.
But holding these discussions, back and forth, is our civilized way of taking seriously the Part 15 opportunity. Please keep agreeing and disagreeing while we sort it all out.
Well the features of this model sound good. I think that instead of a regular compressor/limiter, it should have had an asymmetrical processor. Maybe in the next model that can be implemented? Or perhaps a whole new unit itself as an added product to the lineup!
RFB