"Either he was running at 11 MW or 73 MW"
Wait a minute ... It's a field strength thing which is way over, not input power to final stage, which is also different than output power at the antenna.
It means the antenna had to be longer than legal as well, it's just physics, but they didn't even need to call that into question because that much field strength has the potential for causing interference.
Having said that, it seems a shame they have to shut down a puny little station for small infractions, and let the big boys get away with so much.
For an electrically short vertical monopole above ground, 1 kW of radiated power produces a field strength of 300 mV/m at 1 km. To avoid confusion, I want to point out that I am talking about radiated power from the antenna, not transmitter power applied to the antenna. The radiated power and the transmitter output power are the same only if the antenna system is 100% efficient.
Field strength varies as the square root of the radiated power, and in inverse proportion to distance. We can calculate that 100 mW of radiated power produces a field strength of 100,000 uV/m at 30 m. This is the field strength that can be obtained if the Part 15 AM transmitter and antenna system were 100% efficient.
1 mW of radiated power, which represents 1% transmitter and antenna system efficiency, produces a field strength of 10,000 uV/m at 30 m. This high a field strength usually requires an elevated antenna installation.
10 uW (i.e 10 microwatts)of radiated power, which is very realistic for a ground level Part 15 AM system) represents 0.01% transmitter and antenna system efficiency. This amount of radiated power produces a field strength of 1000 uV/m at 30 m, which is still pretty high compared to the 14 or so uV/m allowed by 15.209.
No need for inspection for 15.219 in this case if Ermi's calculations are correct since the measured field strength cannot be produced by a 15.219 compliant system.
That being said it is unfortunate, as mentioned earlier here, that further details regarding the installation are not available. It appears that the FCC wants to keep the enforcement vague with the less said the better (for them). It is the old saw about not making enough rope to hang yourself.
Neil
Well, I'm not really from Missouri but with all due respect to the several slide rule specialists who insist otherwise, I don't think so. After many years of trying to bring calculated results into the real world in a different field, I remain unconvinced.
Unless someone puts down the pencil, picks up the soldering iron and actually builds a real world circuit that can demonstrate the 100mW DC input transmitter that achieves a consistent 900 microvolts per meter (uV/m) at 1132 meters at 1620 kHz using a 3 meter antenna and a legal, real world ground, I'm not even close to persuaded.
And if you do build a transmitter that achieves those results, the users here at part15.us will line up around the block to buy it from you - I'll even loan you the money to get the production version of the kit to market!
I don't think anyone with or without a slide rule said or implied 900uV/m at 1132m is achievable with a Part 15.219 legal transmitter/antenna.
I'm actually in Missouri, but I don't know what to look for so I'm not sure what should be shown.
Can someone with a slide-rule work backward from the reported power violation and estimate either how much wattage or how much of an antenna was involved?
I still have the second slide rule I used in college. I had lost my first slide rule, and I had to buy another one from the university bookstore for the enormous cost of $16. My lunch in those days was a soft pretzel I regularly purchased near the campus from a street vendor popular with the students. I went without lunch for several days until I made up for the loss of the slide rule. When I finally purchased my next pretzel, the vendor asked, "where were you?"
So here goes: I already said that 1kW of radiated power from an electrically short vertical monopole over ground produces (exactly) 300 mV/m at 1 km. Perfect ground conductivity is assumed. This is a published result. Terman's "Radio Engineering" expressed this rule equivalenly as 186 mV/m at 1 mile. I have calculated this equivalaently as 100,000 uV/m at 30 m to make it more useful for Part 15 AM.
900 uV/m at 1132 m is equivalent to (1132/30)(900) = 33,960 uV/m at 30 m. [(33,960/100,000)^2](100) = 15.5 mW of radiated power, which I reported in a previous post in this thread.
A lot depends on antenna efficiency. I don't have a good antenna calculation program I've been able to use, but there are formulas which should be be able to determine TPO vs. ERP, and thence back to antenna efficiency, which, in turn, should give some values from which we might be able to estimate antenna length and power ratio.
I'd bet it's a long one 😉 ... although the NOUO doesn't state the antenna length. If Ermi's calculations are correct, with the measured FS stated in the NOUO at nearly 30x the legal amount under 15.209(a), it should be possible to figure out a ratio between antenna length and ERP.
If the tuning circuit of the transmitter were modified so that it could feed a quarter wave monopole, the field strength reading can be easily achieved. A long enough ground lead should also be able to obtain the stated field strength, but this would be a very long ground lead indeed.
The NOUO suggests that the FCC has decided that a field strength reading above some limit (maybe above 15,000 uV/m at 30 m -- just a guess)is prima facie evidence that the requirements of Section 15.219 are not met, regardless of what the ground lead length is. In case someone is using a, say, Class EE+ transmitter with a superconductive loading coil, he can argue his claim that he is compliant with 15.219 in his response to the NOUO.
Heh-heh ... Blue sky dream of a lifetime ... OK I'm game ... Maybe Phil B can build us a kit for a Class EE+ transmitter. Then all we need is a few hundred feet of silver/ceramic flexible wire and a few gallons of liquid nitrogen for the superconducting coil 😉
I said in a previous post that the 3m antenna would need to be elevated 20 to 30 ft in order to get 900uV/m at 1132m, using conservative coil and ground resistances and a 100mW input power with a 75% transistor efficiency.
The following results answer the question "what input power is required to get 900uV/m at 1132m with a real world, ground mounted 3m antenna?"
The answer depends a lot on the coil and ground loss resistance of the antenna system.
Results for two different loss resistances:
Coil loss resistance 20 ohms
Ground loss resistance 10 ohms
Required power into the coil: 3.34 watts
Coil loss resistance 5 ohms
Ground loss resistance 2 ohms
Required power into the coil: 788 mW
The first result has loss resistances that would be realistic for a typical coil and an above average ground system with a fairly extensive, but practical ground radial system
The second result could be achieved by using a well designed large air core loading coil and a commercial broadcast quality ground radial system (360 quarter-wavelength wires).
The bottom line is you can't get 900uV/m at 1132m legally.
Although not stated in the NOUO, I think the most likely scenario is that the victim was using a legal 100mW transmitter with an antenna elevated 20 to 30 ft. The FS measurement in this NOUO was a creative way to skirt the elevation issue. This measured FS is higher than can be theoretically achieved with any transmitter that is legal according to 15.209 or 15.219.
That's why I said it was a sad day for Part 15 AM. The FCC is persisting to bust AM operators that are marginally illegal when flagrant pirates are still on the loose.
"That's why I said it was a sad day for Part 15 AM. The FCC is persisting to bust AM operators that are marginally illegal when flagrant pirates are still on the loose."
Yeah. Plus there seems to be questionable practices in commercially licensed stations as well, which are under the gun to make profits in a waning industry or to avoid them for tax purposes as the case may be.
FWIW, I think the FCC is under fire too. A slick-looking website is not going to solve the issues they have with budget cuts, under-staffing, very few monitoring stations. etc. This map isn't particularly reliable, put together about 2.5 years ago:
http://www.0xdecafbad.com/fcc/
... but it looks like a lot fewer than there used to be. Perhaps it means they are taking the shorter path, avoiding the more difficult task of chasing down 'flagrant pirates' on the move. We're much easier targets, and we're likely to give up much quicker rather than run away somewhere else and start up again, like pirates do.
All it takes is a battery pack, a WiFi-connected laptop computer plugged into one of those eBay flamethrowers, and an antenna-in-a-tree. You can pick up the whole package and move it across town in a few minutes, turn it back on and 'Pump Up The Volume' (hmm, I guess I'm assuming everybody has seen that 1990 Christian Slater flick).
Throughout discussions of this kind, talking about "official" field strength findings, we tend to assume the numbers claimed are true and correct, and that the violation is that of the radio operator.
But, for whatever reason, it is possible for field strength numbers to be "incorrect," but the equipment operator could only stand up against such a "mistake" by having an independent measurement by an RF engineer.
The expression "fish in a barrel" fits the Part 15 situation.
it's simple. Licensed Broadcasters Dont Want us there NAB is the mob boss, and fcc is the mob enforcement arm. they have long abandoned protecting spectrum in the public interest and are protecting it for those who can pay
Folks, don't lose sight of what happened here.
"The New York Office received information..." means that the Part 15 station drew enough attention to itself that it incensed someone to the point that they wrote a letter to the FCC.
It takes a lot to motivate someone to write a letter like that. I'm guessing that the station was offensive, or cutting into someone's revenue stream.
And the FCC took it seriously enough to send someone out.
Don't lose sight of where it happened, either. The footprint of that station covered thousands of people. Queens is one of the most densly populated areas of the country.
Maybe I'm naive to believe that someone who is broadcasting as a hobby, soliciting no contributions, selling no ads, and providing quality non-controversial content will continue to broadcast with impunity. But I do.
Steve