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FCC Enforcement Actions for Home FM Transmitters

In our last post we looked at enforcement actions for AM operators and discovered two things:
  1. There aren't very many enforcement actions against AM operators, only around four or five each year.
  2. Enforcement actions centered on very high power operators and the configuration of the transmitter, antenna and ground wires with a focus on the "three meter rule."
Now, a look at the Low Power Radio mailbag tells me that there is similar interest in the FCC actions regarding FM operators, so this time around we'll get an overview of the FM notices and citations.  I reviewed over 300 recent FCC actions against FM operators and there are two messages there, as well:
  1. Unlike the actions against AMers, there are several actions each month against FMers so FMers are really getting lots of enforcement attention.
  2. It's all about the field strength in microvolts per meter, folks, so that's what we really need to discuss.
     So what is field strength and what are "microvolts" per meter or uV/m? The uV/m is a way to measure the practical power output of, in this case, low power transmitters.  For AM operators, permitted uV/m is calculated based on the frequency being used with this formula: (24,000/F)/m at 30 meters, so the lower the frequency the higher the permitted power.
     In FM operations there is no formula.  FM field strength is limited to 250 uV/m at 3 meters, period.  But a hobbyist might ask "what the heck does that mean for me?  To arrive at a useful answer it's important to remember that in the FM world the field strength arises from two factors - the output power of the transmitter and the quality of the antenna match. 
     A transmitter with very low power output (in the microwatt range) could be matched with a very well constructed antenna and would probably violate the letter of the law.  On the other hand, some certified FM transmitters have a rather high power output (perhaps 10 milliwats or 1/100th of a watt) but an intentionally poor antenna system to achieve the 250 uV/m rating.  This is why FCC certified FM transmitters are usually certified as a complete unit including the antenna - and why changing anything on a certified FM transmitter voids the certification.
     My survey of the 300 recent FM enforcement actions shows blatant disregard for the FCC limits (AKA "Pirate Radio" I guess) with field strength readings in the tens of thousands of uV/m at hundreds of meters away. I found only one action that seemed to be in the realm of useful for this discussion.  The relevant portion is here:
     The operation on frequency 107.7 MHz was measured at 1,381 microvolts per meter (uV/m) at 3 meters. This exceeds the allowable unlicensed limit of 250 uV/m at 3 meters established in Part 15.
     So, at just a shade under six times the permitted field strength, we see an enforcement action.  This was the lowest field strength enforced against in my review.  But again, what does this really mean for a hobbyist?  Transmitters are advertised to us with power output in watts, no one gives us field strength until we get busted!  Here is what I have learned through experimentation and yes, I have been busted so I did get the field strength (more on that later).
     I have connected a 10 mW (10 milliwats or 1/100th of a watt) transmitter to a well matched dipole and  the absolute maximum range was 1000 meters using a car radio for reception that has a sensitivity of about 40 uV/m.  What this tells me is that as long as you stay in the sub-watt power output area (10 mW, 100 mW, maybe even 1/2 watt with a not-very-good-antenna) you will likely fall below the enforcement threshold. 
     On the other hand, should you buy one of those FM blow torches off of ebay (2 watts, 5 watts and more), the number of enforcement actions in the FM band indicate you will likely be told to turn it off in a fairly short period of time.  So, what's that like?  My experience was that the quality of the enforcement experience is really up to you.  As long as you are operating at a reasonable (even if not compliant) power level, not advocating sedition and are responsive to the FCC requests, the worst of the experience will be turning off your transmitter. 
     I received my NOUO back in 1997 so it's not online yet, but it looked just like the NOUO referenced above.  My NOUO arrived by certified mail and I responded immediately.  I shut down my transmitter and wrote back that the violation was inadvertent, that I was trying to adhere to Part 15 rules, that the transmitter was permanently off the air and that I would not violate FCC rules again in the future.  I sent that letter certified mail as well and I received a very polite letter back thanking me for my cooperation and telling me that the matter was closed.  Whew!
     So for me the worst part was turning off my transmitter - it does hurt a bit to silence something we hobbyists tend to fall in love with.  I think the message here is try to stay compliant no matter how frustrated you might be by the limited range because a silent transmitter has far less range than a compliant one!
     That, and try AM whenever possible - more range, less enforcement - win/win!


Radio Outlaw said...

If you use a well made EDM or a Ramsey FM30b FM transmitter and keep your content clean; you are highly unlikely to hear from the FCC. However if you use a HLLY transmitter you find on e-bay; you are highly likely to enjoy a visit. The reason is first they create a lot of interference from poor design; and second they put out way to much power for the average user who lacks experience in broadcasting.

We had a HLLY wipe out the video portion of ch 3 & 5; and that was with a quad shielded cable connected to our analog cable system. The HLLY was set to its low power of 1 watt, if it was to set its full 15 watt output; bad things could happen for miles around. Interfering with emergency communications would be highly likely; which could easily generate a complaint and a visit.

Radio Brandy posted images of the interference from a HLLY on its main page; it's pretty bad what a HLLY can due.

Stay away from HLLY's they are just asking for trouble.

EDM and Ramsey's FM30b are very clean RF wise and not likely to cause trouble; unless you jam a legal radio station or go try and sell time (big no no).

The enforcement actions against stock Ramsey & EDM's are nil compared with the many thousands in use across the country.

Broadcast responsibly and keep your programming clean. One more thing! Stay out of the press!

ebay said...

This Blog is great and the info is helpful but would appreciate it if someone could help me specifically.
I own a Belkin TunecastII which wouldn't transmit more than 3'. I was considering a 100mW/.5W xmitter from China on Ebay ($62)to use as a whole house xmitter when I stumbled on a Tunecast mod. Per the instructions I attached a well tuned 55.3" (1/2 wave for 101.5MHz - empty freq. recommended by www.siriusxm/frequency) piece of speaker wire before the attenuater.
Now I get a good 145' of range from the Tunecast. I wouldn't think that such a small xmitter could exceed part 15 but now I am not sure. Is this risky? I am less concerned about freq. I am broadcasting on and more concerned about spikes, transients & harmonic transmissions causing interference.

Any help would be greatly appreciated

Blog Author said...

The 145' range is about what you would expect from legal power levels and a crude antenna. That configuration does not appear to be exceeding Part 15 limits. Operating the FCC maximum of 250 uV/M at 3 M, it's generally agreed that you can expect a range of around 200'. An easy way to check for spurious output would be if you have or know someone who has a scanner - you can check the bands to see if anything shows up.

One thing that might give you some peace of mind is that the transmitter can only output a fraction of the power input. The Belkin TunecastII is designed to run on two AAA batteries so it's drawing milliamps of power and can only transmit far fewer milliamps. Whatever spurious transmissions you might be generating can only be a portion of that.

You can also download a low pass filter schematic and add the filter

You might try a 5/8ths wavelength wire, as shown in this post.

When you alter a certified transmitter the certification disappears and you have an experiment - which is not illegal, just not certified. Certification is only required for selling transmitters. The end user can make one from scratch or modify a certified unit and as long as the field strength is in the neighborhood of spec you're just a low power radio experimenter.

The 100mW/.5W xmitter from China on Ebay will put out a whole lot more mess than the TunecastII, no matter how much wire you connect to the TunecastII :-) Put a .5 watt transmitter on the air (and I certainly couldn't resist the urge to go full power if I had it) and you're not an experimenter, you’re a poor excuse for a pirate. You might as well buy the 30 watt unit and have some real fun before you get your NOUO (kidding - don’t really do that)

StillwaterTownie said...

Who knows how high the power, mabye well over a 100 watts, you can broadcast on an FM pirate station as long as you only broadcast on weekends. After all, I've noticed that the FCC seldom does enforcement activity on weekends. Also operate with a high quality transmitter. No Chinese junk. Choose a frequency not too close to locals. Don't put on obscene programming, or music. And don't try to get the local media to create a story about your station.

Blog Author said...

"Who knows how high the power... as long as you only broadcast on weekends."

Or not - please to be considering the following:

"At approximately 6:50 P.M. on Sunday, March 7, 2010, agents from the Miami Office determined that an unlicensed station was operating from the condominium. After observing the unlicensed station on the air at 10:41 P.M., agents observed the transmitting equipment and found only Mr. Myers present. The unlicensed station continued to transmit until FCC agents disconnected the transmitter, which was located in the residence, at approximately 11:10 P.M. Thus, Mr. Myers was present in the condominium when the unlicensed station was operating on Sunday, March 7, 2010."

Read the full order and see the $5,000 fine here: The Matter of Christopher M. Myers - Memorandum Opinion And Order

Your FCC - Working Nights AND Weekends...

Joe Smoo said...

Some time ago I came across an article that discussed ranges for fm transmitters, it provided the following formula for estimating the range

Assuming a fm receiver with a sensitivity of 50uVolts. The formula was square root of 30 times milliwatts power of transmitter divided by

50uvolts would provide the distance in meters. Using this distance for typical power levels was

10. Milliwatts. =. Sort of 30 x 10 x 10 -3 / 50 x 10 -6 = sqrt .3 / 50 x 10 -6 = .5 x 2000 = 1000 meters.

Now from this they stated that typically the efficiency of antenna systems was 1 to 2 percent so 1000 meters becomes 5 - 10 meters.

10 milliwatts = .54 x 2000 = 1100 meters at 1% eff that's 11 meters.

50 milliwatts. = 1.2 x 2000 = 2400 meters at 1% eff that's 24 meters

100 milliwatts = 1.7 x 2000 = 3400 meters at 1-2% eff that's about 34 meters

500 milliwatts = 3.9 x 2000 = 7800 meters. At 1-2% eff that's about 78 meters

I'm not an antenna guy but putting a high gain antenna on these all bets are off. Now fcc states 250uvolts at three meters, so what will
These trans levels with 1% efficiency be....

If I get 50uvolts at 11 meters I get 100uvolts at 5 meters at 2.5 meters its 200uvolts. So I guess I'm safe with 10 milliwatts

If I get 50uvolts at 24 meters with 50 milliwatts, that's 100uvolts at 12 meters and 200uvolts at 6 meters and 400 at 3 meters so
I may be over fcc limit here ...

If I get 50uvolts at 34 meters with 100milliwatts that's 100uvolts at 17 meters, 200uvolts at 8.5 meters, 400uvolts at 4.25 meters and 800uvolts at 2.12 meters so I'm pretty much illegal at 100milli watt transmitting level... Cause at 3 meters I'm like 400-

So 50milli watts looks barely ok and 10milli watts definitely ok.

I see a lot of low power fm transmitters on eBay using rohm. bh1415 or bh1417 fm chips, now these transmitters typically have one
Or two transistors to bring up the rohm. chip transmit level. The datasheet for this chip say output level is .12 mill I watt, with one amp level might be 1 mill I watt with two maybe 10 milliwatts or less so these should be safe. And fcc compliant assuming only 1% efficiency with antenna system.....

Frank said...

So I bought a SigNStek transmitter. It looks just like the one in the ad at the bottom of this page, except it came with a small fixed antenna. It has 0.5 watt and 0.1 watt power levels. I set it to 0.1 watt.

I'm not running a radio station. I hooked it up to my stereo so I could broadcast the music I'm listening to and pick it up on a radio in another room. I'll use it at most a few hours a week.

Am I going to get in trouble for this?

Low Power Radio Guy said...

While only the FCC can answer that question, your operation isn't in any way similar to any of the actions listed on the FCC's website. When you review enforcement actions you see operators with many times the allowed UV/M, nothing like what you describe. Also, as shown on the Enforcement page, your first contact would be a letter asking you to turn it off. Most of us check distance and harmonic spurs using our own or a friends scanner. If you know someone with a "Police scanner," walk around your property and scan the bands to make sure you're not sending out any junk. Generally accepted Part 15 FM range is a few hundred feet and your operation looks to be in line with that. Have fun!

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