Mr. Russell Johnson Sr.,
I believe there is more room for part 15 carrier current operation than you allow. For openers, the Part 15 Regulations do not limit carrier current to any particular users. Next, On Page 30 of his publication, Mr. Cunningham states that "the largest amount of power the FCC allows you to run into your power lines is 50-watts." However, and this is key, he ads the caveat that "at 100 feet from the building ( and I think elsewhere he also says at 100-feet from the electric wire) YOU MUST COMPLY WITH THE FCC FIELD STRENGTH LIMITATIONS FOR YOUR FREQUENCY OF OPERATION."
Therefore complying with field strength limitations will probably preclude using as much as 50-watts. But in no case is more than 50-watts allowed, regardless of the field readings.
For the individual home it is likely that very little transmitter power would be necessary to reach the allowed radiation limit. The higher powers most likely become necessary in large scale industrial/educational applications. An apartment complex or high rise might increase the amount of necessary power.
The equalizing factor that makes carrier current universally possible is that field reading.
First off, my mother wants to know why I'm called Russell now. LOL.
I do find the comments on this thread fascinating. They range from the rules to publications 20 years old and equipment/projects aimed at international and inner city Christian missionaries. It's a great primer on radio theory and practice while consistently warning that there are FCC rules which are not to be thwarted.
Near the end of the publication it points out that the FCC will not condone using a transmitter that has the potential of operating with excessive output for the intended radio service, even though it is operating legally by having the output attenuated by some means. The FCC doesn't trust everybody to operate "big boy" transmitters in a lesser service. That federal policy remains in effect today in the U.S. Too much box for the intended use equals a citation.
The FCC, in the late 1990's, re-wrote the regulations for Part 15. Not all the staff recommendations were adopted in the final language, hence there are some inconsistencies in the flow of all the Part 15 rules. In other parts of the rules, those inconsistencies in the rules have been update and made whole. Part 15 has not been a priority with the Congress or the FCC.
Bottom line, FCC policy does not allow the use of this transmitter (LPB AM-30) in Part 15 service, ever. It was "type accepted" at manufacture and that fact will not allow it to be used in Part 15 service. Read the label on "type accepted" equipment for further reference. The AM-30 was apparently approved for Part 73 service; a licensed radio service. (note: This site has consistently stayed away from the appearance of support radio piracy.)
Carrier current radio was never intended to be allowed to compete or supplant the licensed services of the Communications Act, even in its present form. Field strength remains the final determining factor of rules compliance in carrier current service. Most users of this service are well acquainted with a radio engineer and his test equipment to ensure compliance.
In 1990, the rules were remarkably different than now. However, many of the tenets and threads of thought of the past regarding federal policy continue today. Part 15 rules of today were never intended to establish a community based micro-broadcast service. But, here we are leading the way in just such a service.
I appreciate your good advice Marshall Johnson, Sr., and I recognize that an especially important point is how rules have changed, and much of the reference material we have comes to us from another time.
Where I am still unconvinced is the question of allowed transmitter power in the design of carrier-current and coaxial cable systems, where the required power to reach legal limits can vary widely from one system to another. 100-milliwatts into a power line won't do the job.
In the case of a cable distribution system it's the 100-milliwatt repeater/antennas that determine compliance, whereas driving the cable sufficiently to maintain needed levels can require a watt or more.
I think the LPB Tech Notes linked up above are of somewhat recent vintage, but may be a little sketchy regarding specifics of power, although they do mention that power may need to be varied depending on individual installations.
More than being a practitioner of these technologies, who knows whether I'll ever build a C-C experiment, I am certainly a student and would hope to be properly informed, so these academic conversations are very welcome.
It has been "traditional" for CC systems to be found on college campuses and so forth. However tradition is not the bottom line when it comes to rules.
Until the rules clearly state CC stations are not allowed to be operated by an individual or operated in a residential setting, CC remains perfectly legal for ANYONE...period.
As long as the station adheres to the emission limits set forth in Part 15 section 221 of 15mv/30m (47.715/f). This measurement must also be on record and kept on site. There is NO rule preventing a CC system from coupling to the neutral or ground. Coupling to the neutral and/or ground of the power grid is the best method to accomplish two things:
1. Drastically reduce or eliminate completely the annoying 60 cycle hum issue.
2. Extend the range beyond the brick wall blocking of utility transformers.
All other technical standards also apply in as far as spurious emissions both in band and out of band (at least 20 db below fundamental). It is also advisable to meet the splatter limitations as well as follow the NRSC curve.
Now the power debate.
100 mW simply cannot push an AM signal through a power grid or building electrical wiring system at all. At most you end up with a very noisy signal 1 room over from where the coupler unit connects to the electrical wiring. Lets also not forget that a building's electrical wiring and the power grid is incredibly low in impedance...typically 1 ohm or less. Now imagine a mere 100 mW trying to shove itself down a 1 ohm or less pipe...be like trying to shove a golfball down a slurpee straw as well as that 100 mW signal being absorbed by the wiring only a few feet down the conduits.
LPB made a number of units for CC setups. The TX-30 is NOT one of them. That model is specifically a PART 73 type accepted unit for licensed use, and ranged in power from 30, 60, and 80-100 watts. Intended for those stations with pre-sunrise and post sunset power requirements.
The most famous LPB unit for CC operation is their TX-2-20 and AM-25 unit. Basically these units, including the TX-30 Part 73 units, all utilized the same power amplifier module and filtering. The final elements were the SD1407 power transistors set up in a push-pull configuration. Other than some component changes on the output filter, and bias settings, they are essentially the same.
My station now operates a carrier current system using an LPB TX-2-20 with a CCUFF C-QUAM exciter board (w/o the added rf power stage), coupling to the neutral AND ground via an LPB TCU-30 coupler. 3 earth grounds and a connection to the cold water pipe at the water meter serves as the grounding.
Output is 5 watts (30 max) with a VSWR of 1:21:1. It covers the entire town with a nice clean AM stereo signal on 1670 Khz. More than enough to provide the coverage and not shoving so much power onto the grid that it is well below the 15.221 emission limit.
Also lets not forget that CC systems work on INDUCTION, not RADIATED EMISSION. CC systems do not use an intentional radiator.
Results vary because of the power grid system and how its configured in a given area. Ground conductivity is also an important factor just as it is for intentional radiator systems (3 meter carrot on the stick).
Carrier current is a viable alternative to extend your Part 15 station's coverage LEGALLY. There are many options to building a CC system that do not require any LPB type gear. Any one of the advertised transmitters on this site can be used followed by an adequate linear amplifier and filtering/coupling circuit, which plans and schematics are abundant across the web.
Injecting the signal into the neutral and/or ground leads is also much safer. Though the neutral wire can have return currents on it, this is not of any major concern unless your trying to couple to a point where the power system is feeding large induction loads, which in turn will induce heavy return currents on the neutral, as well as induce some hum back into the system, and requires frequent coupler peaking. It is best to couple to a low inductive load power feed.
Here's to your success!!
RFB
Thanks for the nice writeup about carrier current. I hope this stimulates some interest in this mode of operation.
In your cite of 15.221 of the rules you must have meant the field strength is limited to 15 microvolts/meter at a distance of 47,715/f(kHz) meters. At 1670 kHz this would be 15 microvolts/meter at 28.6 meters.
I am surprised that the impedance of the power line conductors at RF would be as low as you cited though the power injected does get dispersed quite a bit. When I was involved with campus CC the transmitters used operated from 5 to 25 watts DC final input but I have no idea how much power was delivered to the hot line of the power system. The signals were adequate for in dorm room use.
We had no means of measuring the field strength at the boundaries of the campus but a check with a car radio indicated very weak signals at about 30 feet from the building at the street for the 25 watt unit. Indeed, the power distribution transformers effectively blocked the signals to the point that they were not audible in adjacent dorms just 60 feet away.
I never had the chance to try CC in a residential neighborhood such as where I grew up where one transformer served many homes separated by hundreds of feet. Unfortunately for me my current residence is in a neighborhood with underground power drops and just two homes on the secondary of the distribution transformers.
Carrier current is a relatively easy mode to experiment with but verifying compliance is difficult for most of us.
Neil
The continuance of this thread is welcome, and RFburns comments are resonant with my own beliefs about what the rules say and don't say, what they allow and disallow.
It seems to me Neil's experience of making a document simply describing listening tests at given distances from the power lines would at least demonstrate to the authority that you were taking the best precaution available to you.
In very slow motion I am headed toward an eventual "laboratory" experiment with CC, using some of the circuits published by Ernest G. Wilson, found on this site.
Maybe soon I'll describe exactly what's planned, since this isn't an industrial secret.
I have a Radio Systems model Phase II transmitter (up to 20 watts.) I purchased an LPB Transmitter Coupling Unit (TCU-30) for carrier current coupling to the power line.
I haven't taken the time to really get into it. I did couple to the AC line but found my coverage to be far less than my Talking House with the remote ATU antenna.
The TCU-30 will allow coupling to the AC neutral/ground and up to 3 phases. I've only connected between the HOT and NEUTRAL of a conventional 110 vac outlet.
The TCU-30 GROUND connection is common to the chassi so you can't just reverse the leads to inject into the AC ground. That would put the AC HOT right to the chassi.
Connecting between the NEUTRAL and GROUND wouldn't seem to be a good choice either as these are bonded in the circuit breaker box.
Also, the TCU-30 is connected to the AC ground through the coax jumper to the transmitter so it would seem to be a short when connecting one of the outputs to the AC neutral which is bonded to ground. The branch circuit is only 25 feet from the breaker box.
What would be the correct way to accomplish injecting signal into the neutral?
Thank me for spending 15-minutes digging out 3 references about "neutral loading" into the power line.
1.) Elsewhere on this site, in the Library, look for "Low Power Radio Broadcasting" by James R. Cunningham. Go to Page 34 which describes: UNIQUE METHOD OF CARRIER CURRENT CONNECTION;
2.) Try to locate the LPB Technical Sheet "NEUTRAL LOADING OPTION FOR CARRIER CURRENT INSTALLATIONS";
3.) Search for the LPB Technical Note # 2 and check Page 5 "NEUTRAL LOADING".
Well, I had looked at the LPB method some time ago. They suggest connecting the coupler ground to an earth ground other than the AC power ground and connecting the RF to the AC neutral.
My point is that a good earth ground IS connected to the AC ground which is bonded (connected) to the AC neutral at various points, in my case less than 25 feet between the coupler and the bonding point. Seems that doesn't work in my case.
Running a separate ground wire some distance to a unique ground point would be similar to the old discussion about long ground wires (KENC) to elevated antennas. It would serve more as an antenna than a carrier current delivery system which like a balanced antenna line, doesn't radiate very well.
To MRAM and others, before concluding your judgment on neutral-loading check out "No.1" on my list, the James R. Cunningham method. It is different than that of LPB, and might make a difference. It is the one I have in mind to try.
There is a difference between the power grid neutral and the earth ground connected to it, as well as differences in how power is distributed in various locations.
Here is some info on various earthing and ground configurations in power distribution systems. http://en.wikipedia.org/wiki/Earthing_system
Taken from the article : "The neutral must be connected to the earth (ground) conductor only on the supply side of the customer's disconnecting switch. Additional connections of neutral to ground within the customer's wiring are prohibited."
This means the power company and electrical installers cannot combine the EARTH ground and power grid NEUTRAL at your breaker box or meter. It also means that the physical connection of these two only occurs at the supply point...ie power pole. That wire that runs down every utility pole and into the ground...that is where they are connected..at the top of the utility pole and to the center, highest line..which is the power grid neutral.
Most utility poles are at a distance enough from your coupling point to not be of any significance to actually making a good signal injection of the neutral line with your CC signal at the breaker box. 25 feet distance is more than what I am working with and I am able to inject the signal into the neutral line at the breaker box and get excellent coverage as well as meet the field strength limit of 15 micro volts per meter at 30m (approx 93 feet at 1670).
The neutral line connection of the coupler unit is NOT connected to the chassis in LPB couplers, neither is any of the 3 "hot" connection points. If you examine a schematic, as well as simply look at the PCB board in them, or take a ohm meter and measure across chassis and the neutral connection..you will find there is not a physical or electrical connection.
The neutral line connection on the output side of the coupler is isolated from chassis ground via the toroid transformer, works in the same manner as a service bench isolation power transformer, isolating the source from the load of any direct physical or electrical connection.
I have seen some get so confused on how a short stub across an RF output connection could serve as a coupler to another coupler with another stub across the connection, yet transfer RF energy. Sure at DC you have a SHORT..but at AC...which is what RF is...an AC signal, that stub short is NOT a short. :p
I think this is where your getting confused and thinking that loading the neutral line on the power grid would just dump your signal into ground. Because of the incredibly low resistance of the line, and the nature of the design of the coupler unit, your "INDUCING" an RF signal "ONTO" the neutral wire. This is the BIG difference between "intentional radiator" and a carrier current system.
The Earth ground you should use is a simple copper strap or ground wire ran to a ground rod very close by to the coupler. Extending that ground from the ground rod connection over to another ground rod or more in very close proximity improves the ground return of the signal as well as coupler efficiency.
My set up has the coupler sitting right next to and on top of (in a weather proof enclosure) the main ground rod. Two others are also connected and at a distance of 3 feet from the main ground rod. The power grid neutral connection runs through a short length of conduit which is also earth grounded at the ground rods and back into the wall and up to the breaker box. The connection is made directly to the neutral buss terminal strip as close to the large power grid neutral wire as possible. One wire also connects to the breaker box ground which has the power grid "green" earth ground wire attached. I found this configuration to work best and also improve the VSWR on the coupler, including adding more 60 cycle hum neutralization.
Taking a typical field strength meter by hand and placing its input whip next to the ground system reveals next to no reading even with a direct contact. But take it near the neutral wire of the power grid or that ground wire running down the utility pole and I get a reading on my station's signal. Using a IFR 3000 and Motorola 2200 communications analyzer, the station's compliance measures 13.6 micro volts at 93 feet from the closest neutral wire at the nearest utility pole. Taking all that test gear with a generator 15 blocks down the street, I measure about 8 micro volts at 93 feet from the neutral wire. This is with the transmitter operating at 19 watts RMS.
Obviously inducing an RF signal onto such a low impedance load requires a lot more than 100 mW. It follows through with any circuit, whereas the lower the impedance, the lower the resistance is between signal and ground/neutral and in turn, the more energy required to transfer through it. Like shoving a baseball down a garden hose..would require a bit of "pushing".
Along with the information that can be found here at this site's library on CC configurations, I highly recommend reading up on the power grid distribution configurations and find out which particular one you are dealing with because for each different power grid distribution configuration that is in use..there is a different way to couple a CC system to those varying power grid configurations.
As one writer noted in the information.."Carrier Current is NOT an exact science". This means that experimentation is required, trial and error, by guess by golly. Only two things to remember, keep in mind that it is not an exact science and keep one hand in your pocket while working around energized electrical power systems.
RFB
Unfortunately for me, the local electrical codes allowed bonding the neutral and ground in the breaker box at which point the system earth gound is connected. Perhaps this practice has been changed since 1974.
That being the case, my neutral only runs about 25 feet before connecting to the earth ground.
Aside from the Main breaker in my box, the only "disconnect" would be to pull the meter from its socket. The meter is about five feet from the breaker box. The meter socket has no separate ground connection, rather the neutral is bonded to the meter socket box.
So, in my case neutral loading doesn't seem to work as the bonding point leaves me with a very short neutral.
MRAM, that has always been my understanding. The neutral and service ground are connected to the earth ground rod at the service entrance. That presents a significant short for RF to ground before it reaches out to the power lines.
But, I also know the overhead power lines can radiated significantly, even with a more conventional Part 15 AM transmitter and antenna. The signal can be radiated via the RF ground current flowing in the transmitter ground when the transmitter ground is connected to the AC outlet, either via the neutral or ground wire. The signal usually drops to zero shortly after the point where a pole transformer is located.
The following is not directed to MRAM, but is a more general description of the circumstances.
The ground rod connection is far from perfect. The earth ground rod may have an RF impedance of 30 ohms or more, so that leaves some wiggle room for higher powered, neutral loaded CC transmitters to overcome.
Carrier Current, even with its promise of legal, high power, has never been a factor in the part 15 world. One reason is the rules governing CC require each individual installation to be tested for compliance. That rule is there for a reason. The variables involved with RF ground impedance at the service transformer are so widely variable as to require individual installation verification.
Part of LPBs focus was on carrier current AM transmission. They have gone out of business. There was a heyday for CC many years ago, roughly before FM came into acceptance on the college campuses in the 1960s. Back then, AM CC installations were plagued by hum, but it was a price to be paid for a low-budget college radio station which provided a training venue in addition to having some listeners.
A 5-watt CC transmitter coupled to the neutral of the outlet it happens to be plugged into without further analysis could be a wonderful thing to behold. In a big building with maybe a 100 ft run to the breaker box, the 100 ft antenna, along with the 5 watts and imperfect RF impedance to ground at the box, could radiate immensely. Only installation-specific measurements and verification will determine the actual legality.
On the other hand, if anyone is getting away with it, I say go for it!
Phil
That does present an interesting challenge with such a short run neutral. As I pointed out earlier...power distribution configurations vary slightly even within a few block radius and from one city or town to another.
Its like rolling the dice...take a chance the configurations of the distribution grid will work for you.
One thing I did not mention in my earlier post is that the different configurations of the power grid system will affect how well a CC system functions depending on the frequency used.
You might try a different frequency..perhaps the upper band, which I have found for my installation works far better than using a frequency in the lower portion of the band. That seems to go against the research and documented information in the various reports, but even those reports state that carrier current is not an exact science and that plenty of experimentation is necessary to obtain good results. Nothing different from the experimentation necessary to get good results out of a carrot on a stick.
It is possible that if I were to relocate to another part of town, that my current configuration would not work at the new location and I would have to reconfigure and experiment again to find the best method. My current setup took several days of trial and error to get the good results.
I would also say that just because CC can work for some and not for others does not mean CC is a waste of time or useless. It just so happens to follow what can take place with an intentional radiator with taking a chance on a good ground conductivity rating or poor rating, having to add a ground system etc etc. It will take some work and patience to get that carrot on the stick to do something.
Not every location will be the same and not every installation will be configured the same..even for the carrot on the stick. That being said...it should be taken into account the same variables for CC installations.
It may work...(3 meter stick/CC)....or it may not work. But that is the fun part....finding out what will work....and learn something along the way. 🙂
RFB
Yes, the -20 was replaced by the TR-6000, which will make 30 watts; order the CC version to get max power. On the RS website, look under "Camp Radio" for price info.
The -20's PA transistors are now unobtanium, and RS support was less than helpful in trying to suggest alternates. However, I've run across a couple of possibles - the sticking point is that since the final is Class AB amplifier, the transistors have to be pretty closely matched. I have a couple of -20s, one with a blown PA... I have a couple of ideas about replacements which should work.