Carrier Current

Carl Blare wrote, "If ABMedia1's ("carrier-current") FM station had no output at all, there would be nothing to talk about. But he finds it to be working to his satisfaction."

Just to note that an unlicensed AM-FM system working to the satisfaction of its operator does not necessarily mean that such a system meets the legal basis for it permitted in the U.S. by FCC Part 15.

If such was true, then the FCC would have no basis to cite unlicensed operators who were non-compliant with Part 15 -- even if they were radiating many kilowatts in those bands.

But there are many examples of such citations, shown as NOUOs on the FCC Enforcement Bureau website linked below.

http://transition.fcc.gov/eb/FieldNotices/

It can be shown mathematically that the radiated powers for such cited systems were in the range of very small fractions of one watt, rather than many kilowatts.

The above is offered as a "heads up" to those who might be interested or affected.

Yes, Rich is agreed with by me that simply being "satisfied" with one's Part 15 station does not guarantee FCC approval.

The case of ABMedia1 is approved by the FCC, as ABMedia1 himself has shared with us. That explains part of why I am so supportive of the way he is operating.

ABMedia1 also told us that since getting a thumbs up from the FCC nothing has been changed, therefore ABMedia1's compliant FM station is safe.

The Part 15 rules do describe conditions for operating carrier current radio in the 88-216MHz region, therefore it's not a freak idea, but, as PhilB has shown, referencing the LPB Technical Data Sheet, it is not (generally) considered practical for carrier current broadcasting (the word "generally" is added by me).

But the experimentation idea is what's called for by anyone who cares to set-up and analyze methods of carrier current FM so we can have a report on the results.

ABMedia1 would be the first to admit his is not a laboratory experiment, for the reason that he does not have the expensive field measurement equipment that would be required in documenting his station's performance.

http://www.rfcafe.com/references/electrical/FCC/Part-15/fcc-part-15-radio-frequency-devices-15p611.htm

Very good John WDCX, the BPL Section is very much to the points being discussed.

My print-out of the Part 15 Rules did not include 15.611, so this contributes to my library of knowledge on the subject.

There is more in Part 15 than many users realize, plenty to explore.

With all of the recent statements appearing here on this topic, I decided to ask the FCC directly about whether or not such was authorized.

 Here is their response:

Office of Engineering and Technology

Attachment Details: (none)

Thank you Rich for

A.)  Finding that AFTER ALL carrier current FM is legally possible,

and that

B.)  ABMedia1 is doing fine using a certified transmitter in his station,

and

C.) I was on target by suggesting that ABMedia1's CC FM was legal under 15.239 (field strength being correctly maintained).

It would seem to me that a certified FM modulator could provide a means of very professionally building a CC FM station.

The FCC response in Post #50 here didn't refer to any specific paragraph or snippets of Part 15 defining the limits for carrier current or leaky cable systems for FM, as Part 15 does for AM in §15.221.

FCC §15.209 and §15.219 apply to AM systems using either limited field intensity or limited transmitter power+antenna configuration.  But still the FCC added §15.221 specifically to cover AM systems using carrier-current, and leaky cable radiators.

As the FCC did not add a specific rule to Part 15 for carrier-current and leaky cable radiators in the FM band, this may be an indication that such configurations are not authorized.

This needs more research before reaching the conclusions given in Post #51.  I'll pursue that with the FCC more specifically, and post what develops.

Probably most of us want to know their exact their position on this topic.

Part 15.23 addresses home built Part 15 transmitters.  Quote from FCC OET Bulletin 63:

"Home-Built Transmitters that are Not for Sale

Hobbyists, inventors and other parties that design and build Part 15 transmitters with 
no intention of ever marketing them may construct and operate up to five such 
transmitters for their own personal use without having to obtain FCC equipment 
authorization. If possible, these transmitters should be tested for compliance with the 
Commission's rules. If such testing is not practicable, their designers and builders are 
required to employ good engineering practices in order to ensure compliance with the 
Part 15 standards."

This section would seem to blanket cover ANY Part 15 device as it makes no distinction with  regard to frequency or mode of operation.  If so, certification for an FM transmitter, home  built, would not be necessary.

Part 15.209 seems to agree with that line of reasoning and I quote:

"Radiated emission limits

Section 15.209 contains general radiated emission (signal strength) limits that apply 
to all Part 15 transmitters using frequencies at 9 kHz and above. There are also a 
number of restricted bands in which low power, non-licensed transmitters are not 
allowed to operate because of potential interference to sensitive radio communications 
such as aircraft radionavigation, radio astronomy and search and rescue operations. If 
a particular transmitter can comply with the general radiated limits, and at the same 
time avoid operating in one of the restricted bands, then it can use any type of 
modulation (AM, FM, PCM, etc.) for any purpose."

So although this does not specify carrier current operation it also does not restrict it.

Why they say operation in the 88-108 MHz band must be 15.239 contradicts the chart of info in OET 63 which shows 4 specifications:

88-108 MHz

Intermittent Control Signals 1,250 µV/m@ 3 m A or Q 15.231

Periodic Transmissions 500 µV/m @ 3 m A or Q 15.231

Any (< 200 kHz bandwidth) 250 µV/m @ 3 m A 15.239

Any 150 µV/m @ 3 m Q 15.209 

"...If such testing is not practicable, their designers and builders are required to employ good engineering practices in order to ensure compliance with the Part 15 standards." etc.

But in the case of this thread, do we really know (yet) what configurations will "ensure compliance with the Part 15 standards" for CC/leaky-cable FM, if such standards exist?

Another issue here is that even when a commercial transmitter having FCC certification under §15.239 is modified and used to drive a CC/leaky-cable FM distribution network, this would not mean that such systems automatically were compliant with Part 15 -- because that modified configuration differs from the one used during its certification process.

There are science projects in print showing small circuits for FM wireless mics and other types of transmitters for the FM band, and they are likely made possible by 15.23.

And the other day I reasoned that 15.23 also opens the door on home-building an AM carrier current transmitter, some of them are printed in older papers released by engineers, some of which were linked on this website.

"Seems very reasonable"

"likely made possible"

"the other day I reasoned that"

While such deductions might be true, it would add an immense amount of credibility to such if the bases for those deductions were included in that post, to support its conclusions.

Yes, many times the language used is not unlike that heard on late night radio where the guest will answer a question like, "Do angels really exist," by saying, "Yes, they probably do."

However, the other half of the time I may be leaning on details already given in previous posts within the same thread, in which case I leave it to the reader to keep track of everything.

From Post #56:

"the other half of the time I may be leaning on details already given in previous posts within the same thread, in which case I leave it to the reader to keep track of everything."

I looked back in this thread trying to find any such posts relating to your Post #55, Carl, but not sure I did.

Would you mind listing them here by Post Number?

Many thanks.

That's a huge undertaking, as seen from here looking back over almost 60 posts, but I will follow through and provide that information.

Could we say, maybe, 24-hours?

If anyone wants to post something in the interim go ahead, I'll just not include that in the reconstruction.

Rich, I understand that Part 15.209 is much more restrictive in terms of radiated signal but it is a blanket that covers ANY part 15 device in the AM BCB or FM BCB in lieu of other exceptions such as Part 15.219 and 15.239.  

Part 15.209 doesn't make reference to free radiate, carrier current or other.  So, if a home built FM carrier current installation meets Part 15.209 would that not satisfy the issue of compliance?

Verifying the field strength is the stumbling block.

And since this is carrier current the free radiate field strength is an undesired by-product anyway.  The conducted signal, if power lines would carry it, is where its at.

So, just as Part 15.221 places limits on free radiate field strength for AM BCB carrier current, it is well known that a carrier current station can work.