RFB / Krocks Radio One who is a very knowledgeable broadcast engineer and runs a fully FCC verified (FCC has visited several times and given him a clean bill of health) carrier current system and 15.219 and 15.239 system and who is also in close contact with FCC Denver says part 15 carrier current and leaky cable fm is in fact legal under 15.239 and he mentions as much on this very website in the archives. CCFM is in fact a feasible and viable form of broadcasting. lets not beat this horse to death like we have the ground lead issue!!!!!
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.
Just to note that if there was zero r-f radiation from power lines having CC signals then radio receivers would be unable to receive such signals.
The entry point of the receiver for useful reception of r-f energy is via its antenna, not its power supply.
Like all government agencies, the FCC writes ambiguity into the rules to provide wiggle room for them, not you.
Part 97 is a fine example.
wait.. so.. are ground leads illegal for CCFM? I need to know... :/
Ground leads are of no concern at VHF
i was being a smartass.
Talking about ground leads and CCFM is very significant, because a carrier current system is very much affected by having a firm and substantial electrical ground rod and there is always a ground-lead between RF output and the ground rod.
For CCFM the ground lead CAN'T BE SHORT ENOUGH to produce some result.
+1 Carl - thank you for pointing this out.
I would still love to see the system that abmedia1 put together..
The Transcendent Court is in Session, Judge Carl Blare recusing himself so as to appear as Witness in a Freedom of Information Request from Member Rich.
In Posts # 56 and 58, Rich calls into question Carl's use of the expressions 1.) "...seems very reasonable..."; 2.) "...likely made possible..."; and 3.) "...the other day I reasoned that...".
Further, in Post # 58 Mr. Rich refers to a statement made by Carl in Post # 57: "...the other half of the time I may be leaning on details already given in previous posts within the same thread..."
Following up, Mr. Rich states in Post # 58: "I looked back in this thread to find any such posts relating to your Post # 55 but not sure I did. Would you mind listing them here by Post Number?"
The single Post Number in which the related remarks occur is Post # 55, a self inclusive post, which contains its own answers.
May it further be noted that in Post # 57 Carl said "I may be leaning on details already given." The words "may and be" can be viewed conversely as "may not be."
There being no higher court, this matter is Resolved!
Carl Blare wrote: " ... There being no higher court, this matter is Resolved!"
___________
However the real subjects prompting the post clip above have not been addressed, even though such replies might be amusing to some.
The Member Rich, having presented a provacative argument to the Transcendent Court, has stimulated A Reopened Court, as has never occured in over 3-months of this court's existence.
Let it be said that further discussions depend on presentations and arguments brought before the court by Member Rich.
What say you?
Apparently not covered in this thread is Leaky Coax. Some people may think CC and Leaky Coax are the same because they are mentioned together in 15.221, but they are very different. In one of my previous threads, I quoted LPB as saying CC doesn't work at the FM band frequencies. I should have also quoted the very next paragraph in LPBs document:
"Recently LPB has installed successful unlicensed radiating cable stereo FM systems in colleges. These operate under Section 15.239 of the Rules as revised in 1989. Since these systems are not carrier current, they are not treated further in this document but are covered in LPB Tech Note #6, UNLICENSED FM STEREO RADIATING (LEAKY) CABLE."
Leaky coax is widely available from manufacturers in high quantity. Hopefully there are some distributors that will provide reasonable lengths. Most leaky cables are specified for very high frequencies (uhf and microwave) but some have specified loss ratings going down to 1 MHz. It seems that RG59 leaky cable stands out as being suitable for both 1 MHz (MW band) and 100 MHz (FM band)
Leaky coax works independently of the power lines. It acts just like regular coax except it has apertures in the shield to allow signal to leak out and radiate. It has characteristic impedances of either 50 ohms or 75 ohms, so it can be driven by a 50 or 75 ohm transmitter with adequate low pass filters. The far end of the cable is terminated in a load resistance equal to the characteristic impedance. I assume that for it to be legal, the FM FS limit of 250 uV/m at 3 meters limit would apply to any point along the cable measured at a point perpendicular to the cable. Leaky coax tends to radiate uniformly along its length.
In addition to suggested uses for tunnels and along roadways, it is also suggested for around a building perimeter and inside a building. On campuses, higher FS limits can be used as long as the 250/3 limit isn't exceeded outside the campus property. So it seems leaky coax can be a very practical solution for FM on a campus . Not so much for neighborhood broadcasting, although I can think of one possibility. Suppose you want FM and you live on a fairly sizeable property that is surrounded on all sides with densely spaced houses. Running a leaky coax around the entire perimeter of your property would reach a lot more of those houses than a single legal FM transmitter with a whip antenna.
This would require a lot of experimentation, but at least the concept is backed up by radio theory.
PhilB wrote: "On campuses, higher FS limits can be used as long as the 250/3 limit isn't exceeded outside the campus property."
FCC §15.221(b)(2) permits higher fields on a campus than allowed by §15.209 as long as the §15.209 limit is met at the perimeter of that campus.
FCC §15.221(b) describes the physical area where the limits of §15.209 may be exceeded as "...a college or university campus or on the campus of any other education institution..." It would be unlikely that this definition would be met by the majority of private citizens wanting to exceed the legal field strength limit on their own property.
Another requirement for campus broadcasting is defined for unlicensed AM systems in FCC §15.221(c) -- bold font added for this post. This provision for on-site measurements would require calibrated test equipment and skills that relatively few unlicensed operators would have.
FCC §15.221(c): "A grant of equipment authorization is not required for intentional radiators operated under the provisions of this section. In lieu thereof, the intentional radiator shall be verified for compliance with the regulations in accordance with subpart J of part 2 of this chapter. This data shall be kept on file at the location of the studio, office or control room associated with the transmitting equipment. In some cases, this may correspond to the location of the transmitting equipment."
But all of the above rules apply to radiation in the AM broadcast band, not the FM broadcast band.
Unfortunately there is no explicit provision in Part 15 (so far) for unlicensed FM systems to exceed the 250 µV/m at 3-meter limit of §15.239, even on a legitimate campus.
FCC §15.221(b) describes the physical area where the limits of §15.209 may be exceeded as "...a college or university campus or on the campus of any other education institution..." It would be unlikely that this definition would be met by the majority of private citizens wanting to exceed the legal field strength limit on their own property.
Again I mention FCC ambiguity. "...other education institution..." could include the Madam Garp School of Beauty, John's Neighborhood Radio Training Ranch,... You get the idea. So that being said, if private citizen John includes the Bible Verse of the Day and includes an explication of that verse,he will be legal running CC or leaky cable so long as the prescribe limits are not exceeded.
So.. Any chance of seeing how the ccfm is actually running? I really don't care to nitpick rules... I wanna see cool technology.