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FCC OET Bulletin 63 (link below) is titled UNDERSTANDING THE FCC REGULATIONS FOR LOW-POWER, NON-LICENSED TRANSMITTERS.
Page 29 of this document states:
What is the relationship between “microvolts per meter” and watts?
Watts are the units used to describe the amount of power generated by a transmitter. Microvolts per meter (µV/m) are the units used to describe the strength of an electric field created by the operation of a transmitter.
A particular transmitter that generates a constant level of power (watts) can produce electric fields of different strengths (µV/m) depending on, among other things, the type of transmission line and antenna connected to it. Because it is the electric field that causes interference to authorized radio communications, and since a particular electric field strength does not directly correspond to a particular level of transmitter power, most of the Part 15 emission limits are specified in field strength.
Page 29 goes on to develop an equation to calculate the power needed to produce a specific field intensity at a distance of three meters, assuming a transmit antenna system with a gain of zero dBi (an isotropic radiator):
P = 0.3E^2 where P= power in watts and E = field intensity in V/m
Inserting the field limit of FCC §15.239 on the right side of the equation:
P = 0.3(0.00025)^2 = 0.000 000 018 750 watts, or 18.75 nanowatts
Discussion:
There are many transmitters sold for Part 15 FM use that are rated for hundreds and even thousands of times more output power than legally can be radiated under FCC §15.239.
The FCC has issued citations to some unlicensed operators where it can be calculated that the radiated powers used fall into the range of those produced by transmittters commonly sold and used for Part 15 FM. Here is summary of some of those:
This information is not provided or intended to deter anyone from using/enjoying Part 15 FM, but to give some perspective on the operational realities permitted by FCC §15.239.
Here is a link to FCC OET Bulletin 63:
https://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf
Total posts : 45366Are these considerations or active rules?
Just kidding.
Looking at your chart, there isn’t much room to play around with and you’re right, it does sound scary. I am sure most of us are close if not a bit over when we use those devices, that would be because there isn’t much leeway or room to breath there.
The question is how much over can you unintentionally be, before the field agent decides to issue an NOUO?
I’m not asking as a testing of the waters question, I’m asking just out of curiosity as to how close or how over your device can be before you get that NOUO?
I suppose that would be up to that inspector and how his attitude is and whether he feels you weren’t doing it with the intention of breaking the law I guess.
But I’ll say it again, those numbers do sound scary.
Bruce.
Total posts : 45366I am guessing that these were driven by complaints. Signal levels that low would not automatically draw the ire of the FCC. For example, if one were broadcasting in a neighborhood with regard to the co or adjacent channel and was interfering with a licensed broadcaster, a listener might call the station and say “how come I can’t hear you” or ” am hearing you and someone else.”
Total posts : 45366Regarding: “The question is how much over can you unintentionally be, before the field agent decides to issue an NOUO?” I will comment that it depends.
One factor would be the expected error of measurement for the field strength instrument. If, for example, the error of measurement at the field strength indicated is +/- 10% (a made up n number) then a true signal of 250 uV/m could indicate from 225 to 275 uV/m. A competent operator should know the error band and allow for it. Beyond that it would be a judgement call on the part of the inspector.
That being said, from Rich’s example even the lowest reading cited was no doubt well outside the expected error band exceeding the limit by a large factor and a challenge using the accuracy of the measurement would probably fail.
Some important points are made in Rich’s post. The power out of the transmitter does not guarantee a known field strength and cannot be relied on for compliance and that a very small power can easily produce a field strength which greatly exceeds the limit.
Neil
Total posts : 45366When we buy a certified transmitter we rely on that alone because again watts mean nothing. If the FCC has certified it than we have no other recourse but to take that as scripture (Word Of God). The distance you “Might” receive the said transmitter doesn’t matter. What matters when you the consumer pick up that transmitter off the shelf or you click order now and it arrives at your doorstep is that it has that FCC ID# and the manual says its Certified. That is it to you as a consumer. Oh and that you don’t cause interference to licensed stations and don’t interfere with other radio services. Your certification is a guarantee that as long as you the operator operate the transmitter on a unused frequency far enough away from a used licensed station and your not indending to cause malicious interference. If you have been found to cause interference you the operator have to cease operation until the issue is corrected.
I can imagine some who have been cited were causing issues to other licensed stations as was mentioned several times. So too to be sure you don’t interfere you must test your frequency with very sensitive receivers around the area of which you intend on transmitting. During an inversion on FM go off air for a few seconds and be sure to check because of a distant station is coming in someone may want to hear that station NOT you. If they hear YOU it doesn’t matter their apt to call someone and that will cause a call to the FCC and a complaint will be issued.
Moral of the lecture is this:
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Always use a Certified Transmitter. If you have the certification its ¾ of the law. Keep your box and manuals to it as well. You may need it of something does come up.
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Observe common sense. If you live 200 feet or even a mile of an airport you may think twice about running any FM transmitter. If you live near a military base don’t run one of these transmitters.
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Check your intended frequency several times a day before you purchase your FM Transmitter. Use the legal FM frequencies any licensed station would use aka 88.1, 88.3, 88.5 (Do Not Use Even Numbers after the decimal). I guarantee you some who have got cited were using frequencies too adjacent to a licensed station. Always leave room for example if your using 96.3 that 96.5 and 96.1 are Blank. If your scratching peoples favorite station your gonna get complaints to your local police and or the FCC.
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At regular intervals you play an announcement that your running a FCC certified transmitter and serving (your street here). We play X format. If your receiving any interference we invite you to call (your phone number here) so we can make the necessary adjustments to our transmitter. Once again we hope you enjoy this station and thanks for listening.
All of this should help to avoid any issues as all of this other stuff is only stuff we can’t measure ourselves. This is why I don’t recommend a kit unless you have the proper tools to measure field strength (which most of don’t thus it goes back to the certified Transmitter statement. Want more range? Be sure your buying a certified transmitter reported with the most range. Follow these simple rules and you “should not” have an issue. I’m sure if you operate in a large metro area even if you do follow the rules someone is going to bitch. At that point the only thing I can tell you is that if you live in areas near a field office aka New York, New Jersey, Washington, DC, LA that you think twice about FM broadcasting. Smaller towns your probably less likely to have issues (provided you follow what was stated above).
Now its time to enjoy the hobby.
Total posts : 45366TheLegacy said, “Now its time to enjoy the hobby,” and that’s what I did when I updated a list I keep which shows every FM frequency on the dial, lists all stations on those frequencies within a two-state area including their power, and marking the channels that would be useful for hobby activity.
The last time I updated the list was 2013, so I made many changes to bring it up to date, since so many new signals have popped up and a few translators have relocated.
How amazing it is that I’ve marked NINE (9) frequencies as suitable for use by KDX Worldround Radio!
Take the rest of the week off!
Total posts : 45366Wow that should really have been interesting. These translators are popping up at an alarming rate. It is really something else.
Total posts : 45366Quoting from Reply #5 in this thread…
When we buy a certified transmitter we rely on that alone because again watts mean nothing. If the FCC has certified it than we have no other recourse but to take that as scripture… (etc)
Just a note to newcomers that in the fairly recent past, a well-known situation developed when the FCC cited an unlicensed operator for non-compliance when reportedly using transmitters that were/are Part 15 certified.
Apparently this operator believed that those transmitter/antenna systems were installed and used as recommended by the manufacturer of those transmitters, and that as the transmitters were Part 15 certified, the FCC citations were invalid.
In the end the FCC prevailed, and those operations ceased.
For more information, Google KENC Stayton OR.
Total posts : 45366TheLegacy that is a VERY WELL written statement and makes a lot of sense.
I want to thank you for taking the time to write that out.
That does shed a lot of light on the subject. I am strongly thinking about the AM broadcast band for my future endeavors. I can’t say it won’t work until I’ve been there, done it and see the results.
I have that AM C-Quam transmitter, I have my own ability to listen to my station in stereo using my Realistic TM152, that is as long as I do not go above 1615KHz or at least, I believe that’s where the analog tuner stops on the high end.
Now I have to start coming up with AM broadcast antenna ideas or if I intent to move the transmitter outside in an air tight box and a 102″ steel whip and send the audio and power out to it.
Wish me luck and I’ll take any advice you can offer, but I believe that help should be offered in a topic dedicated to AM broadcasting.
Bruce.
Total posts : 45366KENC was using 3 transmitters each going 10 to 12 blocks and they were transmitting on AM. Now for the AM folks if you want to take this certification thing not meaning anything here’s another double standard for you as I read the Commissioner’s statement. The commissioner said 98 feet in range is the legal range for AM. I guess that would mean that all AMers buying and using 10 foot antennas too are Pirates if you want to take that one as Scripture. SEE I READ THE WHOLE ARTICLE!!!!! Now keep in mind this all happened before the certification of the of the sainSonic FM transmitter. Plus I’m sure this happened before the talking House Transmitter or IAM was certified for AM. I should have copied the link to the article that was in the Oregon press about what actually did happen and the interview. This will also shed some light for those who want to hide behind the mask of part 15 AM and call FM users pirates. Now I read the other post about what certification means. But now you see we have an even larger issue which probably affects everyone of you. AM and 98 feet??? You see my point here I hope. I know everyone of you are only going 98 feet on AM you wouldn’t think of going one foot further. Again double standard one rule doesn’t fit all.
Total posts : 45366For two weeks these threads have been mainly about certified FM transmitters and field strengths relative to 15.239, Part 15 FM.
Turning attention to the KENC legend suddenly has us talking about certified AM transmitters.
At the same time, Rich’s point is that persons convinced they are on safe ground by using certified equipment sometimes find that the unforeseen can render them in violation, especially given the untold background of why KENC ended up being demolished. Proud achievement, sing the praises.
Total posts : 4536618.75 nanowatts is tiny. It is so small accurately measuring it is difficult. It is easier to design a lossy antenna system so the TPO is greater than the allowed ERP. As an example, the C Crane FM2 does not need a resonant antenna because they can get to the max allowed field strength without one. Adding wire to the C Crane’s antenna to make it resonant increases the efficiency of the transmitter thus exciding the allowed field strength.
Anyone can slap a part 15 compliant sticker on a product and sell it on ebay or amazon. If end user of the product gets a visit by the FCC, the violation falls on the end user. The FCC can issue a NOUO, and if the end user pisses off the FCC, a NAL. If the FCC wanted, they could go after the seller of the device, but the end user still could be facing a several thousand dollar fine if the FCC wants to be aggressive.
So it is important to get a transmitter that is actually part 15 certified and use it in a way that will not increase the field strength. Without a field strength meter, that is the only way the end user has some hope of not getting a NOUO.
A transmitter that can do 87.5, 87.7, or 87.9 that has a part 15 sticker is probably not actually part 15 certified.
A C Crane can’t even do 88.1; when they went to certify their transmitter and tested it on 88.1 they may have found emissions below 88MHz that exceeded 100uv/m @3m, so rather than have side band energy fall outside of the FM band they decided to limit how far down their device could transmit. So the part 15 certification of the C Crane transmitter is presumably a valid one.
Total posts : 45366How about the station in Oregon runnng a Talking House? Coincidently the same FCC agent.
Total posts : 45366@post 10/11
I started a thread on KNEC http://www.part15.us/forum/part15-forums/regulations-law/am-and-stayton-oregon
Even if KNEC’s transmitters were certified, they were not installed in compliance with 15.219’s 3m rule.
An AM operating under 15.209 can be mounted as high as the operator wants, just like an FM operating under 15.239 can be mounted as high as the operator wants. Field strength at a distance from the transmitter is the same no matter how high the transmitter is mounted, with the exception of ground reflections.
An AM operating under 15.219 has to be very careful not to break the 3m rule. Certification for 15.219 involves a meter to measure power and a tape measure. The manufacturer supplied antenna can be 3m and the transmitter will pass 15.219. If the end user adds length to the ground, the certification is gone. That is what happened to KNEC.
Total posts : 45366You know I hear talk about the 3 meter ground rule for A AM radio station. But you all are missing the even bigger banner of the picture and what the commissioner said. I will reiterate once again in case the anti FM trolls haven’t figured it out and are still hiding behind an AM radio station. This once again goes to all you 1 mile AM radio stations. The commissioner said the legal output of an AM low power station carries only 98 feet.
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