Even though there is no field strength limit in the part 15.219 rule, the field strength measurement can be used as a "trigger" by the FCC to determine if further investigation and a possible NOUO is warranted.
Suppose a measurement is above some hypothetical "trigger" level. There are two possible reasons. The first is an elevated antenna, and the second is too much transmitter power. After observing a field strength above his trigger level, the inspector will then look for the antenna. If it is observed to violate the 3 meter rule, he is finished and he can go back to the office and issue an NOUO. If he sees no antenna or observes a compliant 3 meter antenna, he may possibly knock on the door to do an inspection. He will be looking for a transmitter running at a significantly higher power than the 100mW limit, or try to determine the nature of the antenna that is causing the higher than expected field strength. Likely if the power is OK, he will find the antenna violates the 3 meter rule.
What is the "trigger" field strength that would cause the inspector to look for the antenna and possibly do an inspection? Consider a "best-case" upper-limit situation for a legal part 15.219 installation:
- 3 meter antenna at ground level
- a very good ground radial system (16 quarter-wavelength radials, each 46.8 meters long at 1600 kHz)
- A highly efficient transmitter (say 95%)
- A super efficient loading coil (say 10 ohms)
- Best ground conductivity possible (salt water, 5000 mS/m)
With this elaborate setup, the field strength at 100 meters will be about 2,650 uV/m. Remember, this is an extreme best-case setup. Also, be sure to note the actual distance of the measurement in the NOUO. Field strength is inversely proportional to distance. The inspector would factor the actual distance before deciding if the measurement exceeds his "trigger" level. He will also likely factor in the actual local ground conductivity. For example if the local ground conductivity is .005 mS/m (Average: pastoral, heavy clay), the maximum expected field strength would drop to 1,350 uV/m.
That's it. There are no other factors. It doesn't matter if the transmitter is certified or not. NOUOs have never contained any information about the transmitter in use. In fact, they have never contained any information about the actual power level.
If you are part 15.219 compliant, you might as well install your transmitter/antenna in your front yard so the FCC agent can easily observe it and drive on.
I don't understand why there is constant controversy and confusion surrounding AM NOUOs. It all seems clear to me. All the discussion and speculation just serves to deter newcomers who want to build a station. Many, probably most, newcomers don't care about microvolts and watts. They only need to understand 100mW and 3 meters.
PhilB posted: Many, probably most, newcomers don't care about microvolts and watts. They only need to understand 100mW and 3 meters.
Unfortunately, these issues are not that simplistic.
Newcomers to Part 15, especially, may not recognize that installing a MW AM transmitter with an attached 3-meter whip at some elevation above the earth, and even with that transmitter operating at 100 mW d-c input power or less to the final r-f stage still can be non-compliant with §15.219(b), depending on the sum of the radiating lengths of the conductors in the antenna system they use.
This sum includes the conductor(s) leading from an elevated transmitter to a functional r-f ground, which for a given transmitter output power can radiate more energy than the 3-meter whip, itself.
Mr. Rich has described a problem.
Now we must find a solution.
Well, I somewhat simplistically stated that all a newcomer needs to understand are 100mW and 3 meters. I was referring to the part 15.219 rule where it states 100 mW max input power and the total length of the antenna, transmission line and ground wire cannot exceed 3 meters. I also discussed only ground mounted antennas in the examples.
Over the years, forums have been flooded with speculation about whether coax feeds are really transmission lines and whether metal masts and audio shields are really ground wires. At this point, these discussions only serve to confuse a newcomer. I am simply stating that a newcomer can feel safe, if he follows the words in 15.219 and need not worry about NOUOs.
A bit of a quibble. Certified transmitters do have a function - if you don't understand microvolts and the like, then you if you are using a certified transmitter, you know that your power is 100mw. All you really have to worry about then is the 3 meters. Even simpler.
The quibble referred to by Artisan Radio is the whole story of Part 15.
What tiny little nibbles of RF opportunity the Part 15 Rules allow.
How petty some of the sticklers for precise adherence.
There is a dimension on the otherside of the happy hobby known as Negative Part 15.
My job as Carl Blare, acting lord, is to bring the negative side out in the open.
But for tonight, back to the dance.
Not quite true. The Rangemaster is certified and has a power adjustment control that is to be adjusted by the user during the tuning procedure. I've never seen any hard data on what the maximum power is, but I've seen anecdotal postings that say it's significantly higher than 100 mW.
On the subtler side, the TH is certified, has no power adjustment, but has an OUTPUT power somewhat over 100 mW as posted on the web by several people who have measured the output power into a 50 ohm resistor. I personally don't look at that as a real problem because the extra power is likely absorbed by losses in the coax and ATU to the point where the field strength would likely be under the hypothetical FCC "trigger" level.
PhilB wrote: ... I am simply stating that a newcomer can feel safe, if he follows the words in 15.219 and need not worry about NOUOs.
Note that to "feel" safe may not equate to being safe from FCC citations to unlicensed operators in the AM/FM broadcast bands.
The FCC legitimately/legally cannot cite unlicensed operators actually complying with Part 15. Part 15 operations are legal, as long as such operators and systems comply with Part 15.
The onus here for those wanting to avoid such FCC actions is fully to understand what is needed to avoid them.
Especially in the case of unlicensed AM operators/operations, that takes more technical backgound than is needed just from reading the words included in FCC §15.219.
Otherwise there would be fewer FCC citations to unlicensed operators in the AM broadcast band.
+ +
Later, Carl Blare posted: ... How petty some of the sticklers for precise adherence. ...
There are no posts about "precise" adherence on this or any other board I've read. Probably you meant to write accurate, rather than precise.
Nevertheless, and as I have posted several time before, unlicensed operators using the AM/FM broadcast bands are free to operate whatever systems they wish, at their own risk.
When a pundit is overly concerned about a small problem he comes to notice.
The one which caused the most controversy and discussion here is the Talking House with ATU antenna system.
The FCC OET test data clearly states the transmitter was connected to the ATU with 8 meters of coax, about 28 feet. This was part of the Certification that was accepted.
Information Station Specialists sells the INFOSPOT system built around the Talking House/I AM Radio transmitter and ATU. Their advertisement states you can use up to 300 feet of coax, not to say putting the ATU 300 feet high, but none the less a vertical separation which they show in their advertisement.
They maintain it is perfectly legal so long as no separate ground wire from the ATU to earth ground is used.
One of our members at Part15 maintains the FCC inspected his elevated ATU installation, smiled and told him to have a nice day as they drove away.
So the question is, Talking House with ATU: Elevated is OK? It would seem too be.
Improperly adjusted, the Rangemaster input to the final stage is around 400mw (at least for my older example).
But the Rangemaster is rather unique (and also garners its share of citations from the FCC, some I'm sure for that very reason).
My point was that if newcomers choose to use a certified transmitter, then (except for the Rangemaster) they only have to worry about the 3 meter rule. I don't see any great technical issues with that rule. You just need to ensure that your feedline + antenna + ground wire doesn't exceed that 3 meters. And recognize that when grounding your transmitter in an elevated install to a metal object, the length of that metal object is considered in the length of the ground wire. This was not always the case in the past, but it is now. It also goes to show that there's an element of interpretation as to how the FCC applies the rules, that trumps the science involved.
Giving front page attention to AM NOUOs is essentially a waste of time and a needless deterrent to newcomers to Part 15 AM.
The FCC database ( http://transition.fcc.gov/eb/FieldNotices/2013.html ) shows a total of 2 AM NOUOs issued so far in 2013 and a total of 2 AM NOUOs issued in all of 2012. I didn't count duplicates and NOUOs issued for operation at 1710 kHz. Does anyone actually believe that these 4 people are the only ones that aren't precisely compliant with part 15.219? Four people in the entire country in a year and a half!
I vote for letting this thread die and leaving the sleeping dogs alone.
...recognize that when grounding your transmitter in an elevated install to a metal object, the length of that metal object is considered in the length of the ground wire. This was not always the case in the past, but it is now. It also goes to show that there's an element of interpretation as to how the FCC applies the rules, that trumps the science involved.
However it is science showing that the top of a long, metal conductor used as a "lightning ground" in an elevated Part 15 AM install is not an electrical ground, and that such a conductor radiates r-f energy over its entire length until it connects to a true r-f ground buried in the earth. This is why that conductor is part of the length of the ground lead included in the 3-meter limit shown in FCC §15.219(b).
A ground lead includes all of the conductors needed to connect to a true r-f ground, in the earth. It is an interpretation/mis-understanding of science to believe otherwise.
As rich says, in fact just about the sole thing he ever says,
"A ground lead includes all of the conductors needed to connect to a true r-f ground, in the earth. It is an interpretation/mis-understanding of science to believe otherwise."
And I ask again, who are you telling? Who are these imaginary people who "believe otherwise?"
But if you run the Rangemaster at 400 mw the audio goes to crap.