Post by part15engineer on Mar 22, 2020 10:52:17 GMT
RFB About AM Stereo 1670 KROCKS Zero Point Radio Part 1
The Following is part one of a two part carrier current tutorial authored by RFB
The Following is part two of a two part carrier current tutorial authored by RFB
Original Article over at K-ROCKS Website complete with links
Part 1
AM Stereo 1670 is a Carrier Current AM radio broadcast station which uses the neutral power grid line to transmit a low level AM radio signal to nearby AM radio receivers. Although this might sound extremely limited in range, the neutral power grid line could cover an entire community or several city blocks. Any typical power socket in a home or business that is also on this same neutral power grid line will be capable of receiving the transmitted signal since these power outlets are connected with one wire to the neutral power grid line to complete the power circuit.
This type of radio service is regulated by the Federal Communications Commision (F.C.C.) in the United States. The section of the FCC Rules that contains these regulations are located in Title 47, Part 15 of the Federal Code. Specific information regarding the Part 15 rules can be found in a public release PDF document and can be accessed by following THIS LINK. The specific sub-part within the document is Pt. 15.221.
During the late 60’s and well into the mid 90’s, Carrier Current AM broadcasting was very common with colleges and universities where students had the opportunity to learn everything involved with radio broadcasting. Although rarely found operating in communities during those years, there were and continue to exist Part 15 low power stations.
Some low power community stations operate under the Part 15.209 rule which allows for an unlicensed radio transmitter in the AM broadcast band using a short antenna and very low transmit power of 100 miliwatts (.01 watt). The antenna, feedline and ground lead if any is used cannot exceed 3 meters in length (aprox 9.6 feet). With a good ground system and no obstructions near the antenna, this flea power signal can extend well beyond 1 and 1/2 miles, with some reports of coverage as much as 3 miles with good conditions!
However even with this range, the signal can experience interference easily and often only receivable in very sensitive radios often found in vehicles and portables in open areas. It is difficult to receive these weak transmitted signals on a typical table top radio inside a home, especially a mobile home where the outer walls are metal, creating a shield preventing good reception. One way to avoid this problem is for the listener to attach an external AM radio antenna such as a “loop” antenna or outside “long-wire” antenna. However the outside long-wire antenna is not always possible due to space limitations, neighbor-friendly issues or hazards.
Carrier Current broadcasting, operated under Part 15.221, is very different from the Part 15.209 specifications. In Part 15.209, the transmitted signal is emitted from an “Intentional” radiator, meaning that the signal is emitted by a conductor such as a rod or wire less than 9.6 feet in length placed into open space, and with a maximum power permitted of 100 miliwatts (.01 watt).
In Part 15.221, the transmitted signal is “Injected” into the electrical utility service wires on the power grid. This forms a “wired” wireless radio transmitting system. Since the power wires have a very low impedance (1 ohm or less), far more transmitting power is needed to effectively send the signal through the power lines. 100 miliwatts would not drive the power lines enough to pick up the signal on a radio a few rooms away. Power levels up to 50 watts are permitted and most Carrier Current stations can provide effective coverage with as little as 10 watts and even 5 watts.
With this method, the radio signal is sent right into any AM radio receiver that is either plugged into a wall outlet, or a portable radio within 200 feet of the power lines. Although the power grid system consists of transformers mounted at various points and will block the transmitted signal by internal shielding, this is overcome by “Injecting” the signal into the power grid neutral wire, which does not pass through the transformers. The neutral wire can be the same neutral wire that is extending for several blocks to several miles delivering the transmitted signal right into the listener’s AM radio.
AM Stereo 1670 KROCKS ZeroPointRadio operates under Part 15.221 into the Casper Wyoming power grid system, injecting the AM 1670 signal onto the neutral power grid line at a nominal power output of 15 watts and a maximum of 50 watts. AM Stereo 1670 KROCKS ZeroPointRadio uses two LPB AM 25 transmitters with the CCUFF C-QUAM and ASMAX C-QUAM exciters and two LBP TCU-30 power line coupling units. One serves as full time operation while the other serves as a standby backup.
In Part 2 of About AM Stereo 1670 KROCKS ZeroPointRadio, we will examine more closely the transmitter systems and power line coupling units as well as go over some basics and history of Carrier Current broadcasting.
RFB
Part 1
AM Stereo 1670 is a Carrier Current AM radio broadcast station which uses the neutral power grid line to transmit a low level AM radio signal to nearby AM radio receivers. Although this might sound extremely limited in range, the neutral power grid line could cover an entire community or several city blocks. Any typical power socket in a home or business that is also on this same neutral power grid line will be capable of receiving the transmitted signal since these power outlets are connected with one wire to the neutral power grid line to complete the power circuit.
This type of radio service is regulated by the Federal Communications Commision (F.C.C.) in the United States. The section of the FCC Rules that contains these regulations are located in Title 47, Part 15 of the Federal Code. Specific information regarding the Part 15 rules can be found in a public release PDF document and can be accessed by following THIS LINK. The specific sub-part within the document is Pt. 15.221.
During the late 60’s and well into the mid 90’s, Carrier Current AM broadcasting was very common with colleges and universities where students had the opportunity to learn everything involved with radio broadcasting. Although rarely found operating in communities during those years, there were and continue to exist Part 15 low power stations.
Some low power community stations operate under the Part 15.209 rule which allows for an unlicensed radio transmitter in the AM broadcast band using a short antenna and very low transmit power of 100 miliwatts (.01 watt). The antenna, feedline and ground lead if any is used cannot exceed 3 meters in length (aprox 9.6 feet). With a good ground system and no obstructions near the antenna, this flea power signal can extend well beyond 1 and 1/2 miles, with some reports of coverage as much as 3 miles with good conditions!
However even with this range, the signal can experience interference easily and often only receivable in very sensitive radios often found in vehicles and portables in open areas. It is difficult to receive these weak transmitted signals on a typical table top radio inside a home, especially a mobile home where the outer walls are metal, creating a shield preventing good reception. One way to avoid this problem is for the listener to attach an external AM radio antenna such as a “loop” antenna or outside “long-wire” antenna. However the outside long-wire antenna is not always possible due to space limitations, neighbor-friendly issues or hazards.
Carrier Current broadcasting, operated under Part 15.221, is very different from the Part 15.209 specifications. In Part 15.209, the transmitted signal is emitted from an “Intentional” radiator, meaning that the signal is emitted by a conductor such as a rod or wire less than 9.6 feet in length placed into open space, and with a maximum power permitted of 100 miliwatts (.01 watt).
In Part 15.221, the transmitted signal is “Injected” into the electrical utility service wires on the power grid. This forms a “wired” wireless radio transmitting system. Since the power wires have a very low impedance (1 ohm or less), far more transmitting power is needed to effectively send the signal through the power lines. 100 miliwatts would not drive the power lines enough to pick up the signal on a radio a few rooms away. Power levels up to 50 watts are permitted and most Carrier Current stations can provide effective coverage with as little as 10 watts and even 5 watts.
With this method, the radio signal is sent right into any AM radio receiver that is either plugged into a wall outlet, or a portable radio within 200 feet of the power lines. Although the power grid system consists of transformers mounted at various points and will block the transmitted signal by internal shielding, this is overcome by “Injecting” the signal into the power grid neutral wire, which does not pass through the transformers. The neutral wire can be the same neutral wire that is extending for several blocks to several miles delivering the transmitted signal right into the listener’s AM radio.
AM Stereo 1670 KROCKS ZeroPointRadio operates under Part 15.221 into the Casper Wyoming power grid system, injecting the AM 1670 signal onto the neutral power grid line at a nominal power output of 15 watts and a maximum of 50 watts. AM Stereo 1670 KROCKS ZeroPointRadio uses two LPB AM 25 transmitters with the CCUFF C-QUAM and ASMAX C-QUAM exciters and two LBP TCU-30 power line coupling units. One serves as full time operation while the other serves as a standby backup.
In Part 2 of About AM Stereo 1670 KROCKS ZeroPointRadio, we will examine more closely the transmitter systems and power line coupling units as well as go over some basics and history of Carrier Current broadcasting.
RFB
The Following is part one of a two part carrier current tutorial authored by RFB
Hello fellow low power broadcasters!
I will begin to describe and outline the details of a Carrier Current broadcast system in this thread.
These series of threads are more instructional and introduction. They will be "sticky" threads and locked so that each part will contain only the provided information. If anyone wishes to reply or ask questions, please do so by starting a new thread with the series part within the title and answers will be provided there. This is to avoid the primary instructional and introduction threads from becoming long with responses and replies.
Although I have posted about my station's Carrier Current system before, those threads and posts mainly focus on my station's setup specifically.
In here will be more detailed information about setting up a Carrier Current system, as well as outlying the many obstacles and solutions that come along with it.
I have installed over 175 Carrier Current systems in the 30+ years as a broadcast television and radio engineer. Many of them were systems for churches, mobile home parks, campgrounds like KOA locations and parks and recreation facilities. I have even installed some systems for businesses like shopping malls and large event arena parking lots like football fields and racing car facilities.
Carrier Current..or CC for short, is a very unique method of broadcasting to a limited area. CC is regulated under FCC Part 15.221 of the Telecommunications Act of 1934. It is a license free radio broadcasting service and can generate revenue through commercial advertising.
CC has been around for a very long time. In the 1920's, early electric power companies and telephone companies used CC to communicate with their remote switch stations, and even used as early voice carrier systems on single wires for the telephone companies of the time, prior to the establishment of POTS..(Plain Old Telephone Service) two-wire DC systems. In those years, which industries were still establishing standards, long distance communication was very difficult for voice and the most reliable communications at the time was teletype or Morse Code sent via DC pulses down long runs of wires.
In the 1940's during World War II in the United States, over the air radio transmissions were strictly regulated and no personal two way radio communications were permitted during the war. That left many licensed HAM operators without the means to communicate with over the air signals sent via an antenna. Their only choice open was to experiment and work with the CC technique. And they were successful!
In the 1960's a company was born to produce the only options to broadcasting for CC operations. That company was called Low Power Broadcasting Inc, or LPB. They were the mainstay and primary source for CC equipment for years. They also produced low power AM transmitters for licensed Part 73 broadcasters who had to operate at low power levels below 250 watts at night, and some of those licensed stations are still using their LPB gear today!
That company went out of business in 1998 after being bought by a group who really had no idea what the business was about. It was literally shredded and ground to dust according to the former engineers who had worked with that company since it began.
Very little information is available regarding CC systems and operations. However tid bits of information have dripped out over time. Many of the ground level engineers who designed and built
CC stations are gone and have passed on their knowledge to others, who are now either retired or also passed on. The big gap in available information is because CC was considered as a trivial or side subject to the likes of a footnote in an article. However even with that, the dedicated people of CC continued and expanded on the technology..enough so that a new company called Radio Systems began and started selling their own version of CC equipment!
Today the gap still remains in available information. I am one of the lucky ones who was there in the very early years of CC and have retained all of the information and experience with CC systems, and am happy to pass that on in a more open and public way..right here at my station's forum!
Let's not take it for granted. CC is a very unique and often very difficult system to understand. However it is also an incredibly easy system to maintain and operate, and can generate income only limited by one's imagination. A CC station can generate thousands of dollars of monthly income. The possibilities are indeed endless.
The equipment however is no longer manufactured and can only be found at auction sites or at estate sales or perhaps found at a commercial station's transmitter site being unused. Over the last 10 years I have seen LPB gear being auctioned on ebay on a regular basis. However that should not
be a discouragement as the company Radio Systems still manufactures CC equipment, though it is rather pricey.
In Part two I will begin to describe the in's and out's of how the CC system works and the methods of coupling to the power grid.
Stay tuned!
RFB
I will begin to describe and outline the details of a Carrier Current broadcast system in this thread.
These series of threads are more instructional and introduction. They will be "sticky" threads and locked so that each part will contain only the provided information. If anyone wishes to reply or ask questions, please do so by starting a new thread with the series part within the title and answers will be provided there. This is to avoid the primary instructional and introduction threads from becoming long with responses and replies.
Although I have posted about my station's Carrier Current system before, those threads and posts mainly focus on my station's setup specifically.
In here will be more detailed information about setting up a Carrier Current system, as well as outlying the many obstacles and solutions that come along with it.
I have installed over 175 Carrier Current systems in the 30+ years as a broadcast television and radio engineer. Many of them were systems for churches, mobile home parks, campgrounds like KOA locations and parks and recreation facilities. I have even installed some systems for businesses like shopping malls and large event arena parking lots like football fields and racing car facilities.
Carrier Current..or CC for short, is a very unique method of broadcasting to a limited area. CC is regulated under FCC Part 15.221 of the Telecommunications Act of 1934. It is a license free radio broadcasting service and can generate revenue through commercial advertising.
CC has been around for a very long time. In the 1920's, early electric power companies and telephone companies used CC to communicate with their remote switch stations, and even used as early voice carrier systems on single wires for the telephone companies of the time, prior to the establishment of POTS..(Plain Old Telephone Service) two-wire DC systems. In those years, which industries were still establishing standards, long distance communication was very difficult for voice and the most reliable communications at the time was teletype or Morse Code sent via DC pulses down long runs of wires.
In the 1940's during World War II in the United States, over the air radio transmissions were strictly regulated and no personal two way radio communications were permitted during the war. That left many licensed HAM operators without the means to communicate with over the air signals sent via an antenna. Their only choice open was to experiment and work with the CC technique. And they were successful!
In the 1960's a company was born to produce the only options to broadcasting for CC operations. That company was called Low Power Broadcasting Inc, or LPB. They were the mainstay and primary source for CC equipment for years. They also produced low power AM transmitters for licensed Part 73 broadcasters who had to operate at low power levels below 250 watts at night, and some of those licensed stations are still using their LPB gear today!
That company went out of business in 1998 after being bought by a group who really had no idea what the business was about. It was literally shredded and ground to dust according to the former engineers who had worked with that company since it began.
Very little information is available regarding CC systems and operations. However tid bits of information have dripped out over time. Many of the ground level engineers who designed and built
CC stations are gone and have passed on their knowledge to others, who are now either retired or also passed on. The big gap in available information is because CC was considered as a trivial or side subject to the likes of a footnote in an article. However even with that, the dedicated people of CC continued and expanded on the technology..enough so that a new company called Radio Systems began and started selling their own version of CC equipment!
Today the gap still remains in available information. I am one of the lucky ones who was there in the very early years of CC and have retained all of the information and experience with CC systems, and am happy to pass that on in a more open and public way..right here at my station's forum!
Let's not take it for granted. CC is a very unique and often very difficult system to understand. However it is also an incredibly easy system to maintain and operate, and can generate income only limited by one's imagination. A CC station can generate thousands of dollars of monthly income. The possibilities are indeed endless.
The equipment however is no longer manufactured and can only be found at auction sites or at estate sales or perhaps found at a commercial station's transmitter site being unused. Over the last 10 years I have seen LPB gear being auctioned on ebay on a regular basis. However that should not
be a discouragement as the company Radio Systems still manufactures CC equipment, though it is rather pricey.
In Part two I will begin to describe the in's and out's of how the CC system works and the methods of coupling to the power grid.
Stay tuned!
RFB
The Following is part two of a two part carrier current tutorial authored by RFB
In this part I will explain the basic function of a Carrier Current system and what's involved in making it work.
A Carrier Current system is nothing more than a "Closed Loop" system, meaning our radio signal is confined within a loop comprising of a buildings electrical wiring, or a leaky coax, or a simple wire.
The most easiest way to understand this is thinking of a lasso loop, or cowboy's lasso rope. The lasso rope has a certain size, and our signal is injected onto this lasso loop. The loop is confined to a specific area, just as the cowboy's lasso loop is of a certain size. The signal injected onto this loop will remain on the loop and only emit away from the loop a specific distance.
The distance in which the signal can emit away from the loop is determined by the formula 157,000 divided by frequency of operation equals the distance away the signal must be at 15 microvolts field strength, which is pretty much in the noise floor of the AM band. A Carrier Current signal works in the near field/induction field. We do not want our signal to produce a far field signal like traditional systems feeding a monopole antenna system. We want to confine our signal on the loop and within the maximum allowed signal strength away from the loop per the formula.
In order to achieve this, it is absolutely necessary to use a proper coupling device to inject the signal onto the electrical wiring or single wire forming the loop, for a couple of good reasons. When injecting a signal onto power wires, the power wires are constantly changing inductance due to electrical loading from appliances, lights and other electrical loads. When this happens, the power wiring introduces a big shift in loading inductance which the transmitter will most likely not agree with, causing serious loading mismatches.
A proper coupler will keep the changing load from affecting the transmitter, as well as maximize the signal injection during the load inductance changes. A proper coupler also prevents any return AC currents from going back into the transmitter which otherwise a very annoying hum would be heard in the signal. The LPB TCU-30 coupler for example, has a 3000:1 isolation ratio in the reverse direction, practically eliminating any return AC currents from re-entering the transmitter output and inducing 60 cycle hum onto the final output of the transmitter. If the isolation was not there, the 60 cycle hum would literally modulate the final circuit of the transmitter and be amplified by the transmitter's final amplifier and pass it on to the listener's radio.
Some information on the web suggests using a simple high voltage capacitor and fuse to inject the signal onto the power wires. This is not recommended as this quickie coupler is very dangerous, and does not provide proper matching for the transmitter, nor does it provide return 60 cycle hum rejection. It can also cause our confined signal to emit much further off the line than legally allowed. It can also cause unwanted spurs and harmonics to pass onto the power wiring and fill the AM band with a lot of unwanted junk. And when the power lines change inductance due to loading changes in a given day, those unwanted signals and junk can increase tremendously and cause interference across the AM band, as well as into other segments of the radio spectrum, something we certainly do not want!!
Besides the traditional method of coupling to the power lines, neutral loading is another method to couple the signal onto the power lines and is not a new concept. Neutral loading was widely used in cases where the other methods would not work satisfactorily due to intense inductive changes and/or excessive 60 cycle return hum. Neutral loading is also creating a lasso loop just like coupling to the main hot lines, with the exception that we introduce an isolated Earth ground to complete the loop.
In a traditional configuration, the coupler is connected between the hot wires and neutral wire, where the loop completes via the mains step down transformer winding. In neutral loading, the loop is formed between the grid neutral wire and the isolated Earth ground. This may not seem like a loop, but is because the dirt is conductive with a certain amount of resistance. When a ground rod is pounded into the dirt, that forms one side of the loop, and the neutral line where our signal is injected, completes the other end of the loop. The dirt itself becomes the final connection between the two points of the ground rod and neutral line. Basically it becomes a very WIDE lasso loop, and can carry our signal for blocks or even miles depending on the power grid configuration in a given area.
The maximum signal emission with neutral coupling must follow the same maximum limits in the formula given above. It means our signal cannot travel away, or off the line any further than the maximum distance given in the formula, but that does not prevent our signal from traveling DOWN RANGE on the line for as far as it can go. Depending upon the grid configuration, that signal could travel DOWN RANGE on that line for miles! Since every home and business has a neutral wire ran into them for AC power return, our signal will go into every home and business tied to that neutral line!
Nearby induction can take place if the power lines are in close proximity, helping our signal couple through the air gap between these runs of power lines and onto the next set of lines! Though the signal will be quite weak, it does couple enough for the signal to be detected, and even listened to like listening to a distant station. Added couplers are used to join to the next set of power lines and neutral by running a 2nd transmitter and coupler, or feeding the 2nd coupler from a coax carrying the main signal.
Because we are working inside and within a certain distance off the loop, we do not want to shove too much signal onto that loop otherwise the signal will over-saturate radio receivers and make our station sound nasty, and no one wants to listen to a nasty signal! Also injecting too much signal onto the lines can make the signal travel much farther away from the line than permitted by Part 15.221 rules. The system should be adjusted so that adequate coverage is obtained while keeping it within the 15.221 limits for non-licensed operations.
Using proper field strength measuring equipment to check for the system's limits is often outside of most budgets as those field strength measuring equipment can cost thousands of dollars and more. However a much cheaper and simpler method can be used to approximate the system's compliance to 15.221.
The best simpler method is to use a battery powered pocket radio and listen for our signal to drop into the noise floor at the given distance from the formula.
For example..a CC system is operating at 600Khz. The formula is 157,000 divided by 600 equals 261.66 feet, or rounded out to 262 feet. This means that at 262 feet AWAY from the line, our signal must be in the noise floor or just barely detectable by the radio. Again this does not mean our signal can only travel DOWN the wire 262 feet. It means our signal cannot emit AWAY or OFF that line no further than 262 feet.
The signal picked up by the portable radio should sound like your tuned to a very distant station with some noise. Although this method is not nth degree accurate, it is a very close approximate method that demonstrates your attempt at making the system Part 15.221 compliant.
After the revision of the FCC Part 15 rules in 1989, any new Carrier Current system must have the system checked by a qualified radio technician with recognized measuring equipment, and all measurements must be kept on file at the station's transmitter location. Any system set up prior to 1989 are "grandfathered" and do not have to maintain these measuring records, however they still must meet the signal limit requirements. It is a good practice to maintain records anyway for peace of mind.
There is this misconception by many that the only measuring equipment recognized by the FCC is the Potomac FIM 21 and 41. This is NOT TRUE!! There are thousands of two way radio shops and cell phone technicians that use other measuring equipment than the Potomac instruments and are just as accurate and reliable in FCC field strength measuring, and quite acceptable by the FCC field agents as well as recognized as being adequate enough. If those other instruments were not recognized by the FCC as adequate, the rules would specify a particular type of measuring gear throughout the entire Title 47 of the Code of Federal Regulations, to which it does not.
Plus on top of that, these two way radio shops and cell tower technicians and companies would have had to invest in millions of dollars in Potomac field strength meters and no doubt they would be quite worried all the time with tower climbers who might accidentally drop one of those 10 grand field strength meters from atop a tower! Though this is a remote possibility, it can happen as I personally have seen tower climbers accidentally drop tools and other things while working at those elevated levels. Nothing is 100 percent perfect, even tower workers and things do get dropped from time to time.
Look out below!
In any case, there are good engineering practices that can be used to ensure your CC system is meeting compliance with 15.221, without the nay saying and preaching by stuck in stone age mentalities. I use a Motorola R 2012 D and an HP 8590 to measure my system's compliance, and I even have a senior FCC field agent's blessing and recognition to the use of those two pieces of equipment that he describes as "proper and adequate for measuring" my system's compliance. Needless to say, he was quite impressed how accurate they were compared to his Potomac meters when my stations were inspected less than a year ago, and two other times prior to that, spanning a total of 4 years. My test equipment was within 1 percent accuracy to his Potomac!
In the next installment I will go into detail on the various lasso loop configurations in detail, specifically the most safe and best CC coupling method..neutral coupling.
Low Power Hour #7 (RFB on Carrier Current)
Low Power Hour #13 (RFB on Carrier Current)
Low Power Hour #14 (RFB on Carrier Current)
RFB
A Carrier Current system is nothing more than a "Closed Loop" system, meaning our radio signal is confined within a loop comprising of a buildings electrical wiring, or a leaky coax, or a simple wire.
The most easiest way to understand this is thinking of a lasso loop, or cowboy's lasso rope. The lasso rope has a certain size, and our signal is injected onto this lasso loop. The loop is confined to a specific area, just as the cowboy's lasso loop is of a certain size. The signal injected onto this loop will remain on the loop and only emit away from the loop a specific distance.
The distance in which the signal can emit away from the loop is determined by the formula 157,000 divided by frequency of operation equals the distance away the signal must be at 15 microvolts field strength, which is pretty much in the noise floor of the AM band. A Carrier Current signal works in the near field/induction field. We do not want our signal to produce a far field signal like traditional systems feeding a monopole antenna system. We want to confine our signal on the loop and within the maximum allowed signal strength away from the loop per the formula.
In order to achieve this, it is absolutely necessary to use a proper coupling device to inject the signal onto the electrical wiring or single wire forming the loop, for a couple of good reasons. When injecting a signal onto power wires, the power wires are constantly changing inductance due to electrical loading from appliances, lights and other electrical loads. When this happens, the power wiring introduces a big shift in loading inductance which the transmitter will most likely not agree with, causing serious loading mismatches.
A proper coupler will keep the changing load from affecting the transmitter, as well as maximize the signal injection during the load inductance changes. A proper coupler also prevents any return AC currents from going back into the transmitter which otherwise a very annoying hum would be heard in the signal. The LPB TCU-30 coupler for example, has a 3000:1 isolation ratio in the reverse direction, practically eliminating any return AC currents from re-entering the transmitter output and inducing 60 cycle hum onto the final output of the transmitter. If the isolation was not there, the 60 cycle hum would literally modulate the final circuit of the transmitter and be amplified by the transmitter's final amplifier and pass it on to the listener's radio.
Some information on the web suggests using a simple high voltage capacitor and fuse to inject the signal onto the power wires. This is not recommended as this quickie coupler is very dangerous, and does not provide proper matching for the transmitter, nor does it provide return 60 cycle hum rejection. It can also cause our confined signal to emit much further off the line than legally allowed. It can also cause unwanted spurs and harmonics to pass onto the power wiring and fill the AM band with a lot of unwanted junk. And when the power lines change inductance due to loading changes in a given day, those unwanted signals and junk can increase tremendously and cause interference across the AM band, as well as into other segments of the radio spectrum, something we certainly do not want!!
Besides the traditional method of coupling to the power lines, neutral loading is another method to couple the signal onto the power lines and is not a new concept. Neutral loading was widely used in cases where the other methods would not work satisfactorily due to intense inductive changes and/or excessive 60 cycle return hum. Neutral loading is also creating a lasso loop just like coupling to the main hot lines, with the exception that we introduce an isolated Earth ground to complete the loop.
In a traditional configuration, the coupler is connected between the hot wires and neutral wire, where the loop completes via the mains step down transformer winding. In neutral loading, the loop is formed between the grid neutral wire and the isolated Earth ground. This may not seem like a loop, but is because the dirt is conductive with a certain amount of resistance. When a ground rod is pounded into the dirt, that forms one side of the loop, and the neutral line where our signal is injected, completes the other end of the loop. The dirt itself becomes the final connection between the two points of the ground rod and neutral line. Basically it becomes a very WIDE lasso loop, and can carry our signal for blocks or even miles depending on the power grid configuration in a given area.
The maximum signal emission with neutral coupling must follow the same maximum limits in the formula given above. It means our signal cannot travel away, or off the line any further than the maximum distance given in the formula, but that does not prevent our signal from traveling DOWN RANGE on the line for as far as it can go. Depending upon the grid configuration, that signal could travel DOWN RANGE on that line for miles! Since every home and business has a neutral wire ran into them for AC power return, our signal will go into every home and business tied to that neutral line!
Nearby induction can take place if the power lines are in close proximity, helping our signal couple through the air gap between these runs of power lines and onto the next set of lines! Though the signal will be quite weak, it does couple enough for the signal to be detected, and even listened to like listening to a distant station. Added couplers are used to join to the next set of power lines and neutral by running a 2nd transmitter and coupler, or feeding the 2nd coupler from a coax carrying the main signal.
Because we are working inside and within a certain distance off the loop, we do not want to shove too much signal onto that loop otherwise the signal will over-saturate radio receivers and make our station sound nasty, and no one wants to listen to a nasty signal! Also injecting too much signal onto the lines can make the signal travel much farther away from the line than permitted by Part 15.221 rules. The system should be adjusted so that adequate coverage is obtained while keeping it within the 15.221 limits for non-licensed operations.
Using proper field strength measuring equipment to check for the system's limits is often outside of most budgets as those field strength measuring equipment can cost thousands of dollars and more. However a much cheaper and simpler method can be used to approximate the system's compliance to 15.221.
The best simpler method is to use a battery powered pocket radio and listen for our signal to drop into the noise floor at the given distance from the formula.
For example..a CC system is operating at 600Khz. The formula is 157,000 divided by 600 equals 261.66 feet, or rounded out to 262 feet. This means that at 262 feet AWAY from the line, our signal must be in the noise floor or just barely detectable by the radio. Again this does not mean our signal can only travel DOWN the wire 262 feet. It means our signal cannot emit AWAY or OFF that line no further than 262 feet.
The signal picked up by the portable radio should sound like your tuned to a very distant station with some noise. Although this method is not nth degree accurate, it is a very close approximate method that demonstrates your attempt at making the system Part 15.221 compliant.
After the revision of the FCC Part 15 rules in 1989, any new Carrier Current system must have the system checked by a qualified radio technician with recognized measuring equipment, and all measurements must be kept on file at the station's transmitter location. Any system set up prior to 1989 are "grandfathered" and do not have to maintain these measuring records, however they still must meet the signal limit requirements. It is a good practice to maintain records anyway for peace of mind.
There is this misconception by many that the only measuring equipment recognized by the FCC is the Potomac FIM 21 and 41. This is NOT TRUE!! There are thousands of two way radio shops and cell phone technicians that use other measuring equipment than the Potomac instruments and are just as accurate and reliable in FCC field strength measuring, and quite acceptable by the FCC field agents as well as recognized as being adequate enough. If those other instruments were not recognized by the FCC as adequate, the rules would specify a particular type of measuring gear throughout the entire Title 47 of the Code of Federal Regulations, to which it does not.
Plus on top of that, these two way radio shops and cell tower technicians and companies would have had to invest in millions of dollars in Potomac field strength meters and no doubt they would be quite worried all the time with tower climbers who might accidentally drop one of those 10 grand field strength meters from atop a tower! Though this is a remote possibility, it can happen as I personally have seen tower climbers accidentally drop tools and other things while working at those elevated levels. Nothing is 100 percent perfect, even tower workers and things do get dropped from time to time.
Look out below!
In any case, there are good engineering practices that can be used to ensure your CC system is meeting compliance with 15.221, without the nay saying and preaching by stuck in stone age mentalities. I use a Motorola R 2012 D and an HP 8590 to measure my system's compliance, and I even have a senior FCC field agent's blessing and recognition to the use of those two pieces of equipment that he describes as "proper and adequate for measuring" my system's compliance. Needless to say, he was quite impressed how accurate they were compared to his Potomac meters when my stations were inspected less than a year ago, and two other times prior to that, spanning a total of 4 years. My test equipment was within 1 percent accuracy to his Potomac!
In the next installment I will go into detail on the various lasso loop configurations in detail, specifically the most safe and best CC coupling method..neutral coupling.
Low Power Hour #7 (RFB on Carrier Current)
Low Power Hour #13 (RFB on Carrier Current)
Low Power Hour #14 (RFB on Carrier Current)
RFB
