Lately, there seems to be a resurgence of interest in Carrier Current transmission. This is a technology that goes back to the 1940s. There seems to be perception that Carrier Current offers a way to achieve a much wider coverage area within the confines of the Part 15 rules.
In the heyday of Carrier Current (1950s - 1970s), it was widely used on college campuses. A typical configuration involved distribution of RF from a central source over coax lines to individual amplifiers located in each building. The output of the amplifiers was then coupled into the power wiring in each building. It was well known that the signal would not go much beyond each building due to blocking by the AC power distribution transformer, but was very strong within the building. More often than not, the signal had an annoyingly high level of AC hum, but that was generally tolerated because the concept of actually having a college radio station was more important. Subsequently, AM carrier current was replaced with an FM transmitter and/or by on-campus distribution over TV cable.
Until recently, there were only two remaining manufacturers of carrier current equipment in the US: LPB Communications and Radio Systems Inc. Since LPB has stopped sales, Radio Systems is the only one left. Obviously demand has waned.
A Google search for Carrier Current doesn't turn up any information that supports the idea that a wonderful new expanded coverage area is actually achievable. In fact, documents from LPB that still linger on the web specifically state that reception beyond the AC distribution transformer falls off greatly and coverage of more than one campus building from a single injection point is unlikely.
The present-day scenario for Part 15 carrier current mainly focuses on the transmitter being located in a single home served by an AC distribution transformer which also serves a small cluster of maybe 10 to 15 other nearby homes. The transformer blocks the signal beyond those homes, so coverage is limited to those homes at best. A 5 to 10 watt transmitter is required to overcome the extreme losses encountered in the AC wiring.
Often, it is mentioned optimistically that the power company may have RF bypass devices across the transformers that would allow the signal to propagate over a wider area. These are called "CT Couplers", www.narucmeetings.org/Presentations/current-telecom0704.pdf, and are part of the Access BPL (Broadband over Power Line) system. BPL has been deployed in a limited number of areas for test, has proven to cause RF interference, and in many cases has been taken out of service. It is not likely to continue into widespread deployment.
So, this new interest in Carrier Current doesn't seem to make much sense. Of course, it has been proven to work within its known constraints, but it doesn't sensibly offer expanded range relative to a good single Part 15.219 transmitter installation. In fact, given the typical single-home scenario, it seems to offer a smaller or, at best, equivalent range.
..of encouragement.
NOT.
Let me do some more clarifying to add to the above encouragement.
It is correct that BPL has been a concern for cause of interference, mostly by HAM radio operators within their operating bands. BPL is used across a wide range of frequencies including the MW and HF bands..well up to 70Mhz in some locations.
The BPL service was originally intended to deliver high speed broadband internet service to remote areas where DSL and Cable were impractical or not profitable..such as in locations with very low population.
However, even with the "cry wolf" from the HAM's, CC on the MW band DOES NOT CAUSE ANY interference to ANY of the HAM bands...unless a setup is installed incorrectly or the transmitter is spitting out tons of spurious junk.
Rest assured, the units manufactured by LPB and Radio Systems DO NOT output any junk, especially the LPB units. Although designated as Carrier Current transmitters, every single LPB unit made, both tube and solid state units, exceed Part 73 specifications. In fact, since the first series of solid state units, every single LPB transmitter uses the same designs and components for the CC systems AND the Part 73 systems for pre sunrise and post sunset/overnight reduced power operations.
There are quite a few licensed AM stations that must reduce power at night lower than 250 watts that use LPB transmitters, the same designs and components found in the CC transmitters.
It is also true that very little information can be found on the web about CC. However there are community stations and their owners today who can provide plenty of information.
Another "myth" about CC is that it is only permitted on college campuses. BS. It has only been "tradition" that CC systems would be found on college campuses in the early years of CC.
CC systems have been used in mobile home parks, drive in movie theaters, churches, tourist parks like Carlsbad Caverns, and even used as early "TIS" systems by running leaky coax along segments of interstate highways and some state highways. And yes, even in those years, neighborhood CC stations were around, though not common, they were there and did provide a valuable service.
CC systems require a lot more than simply hooking up a wire tacked to the ceiling by a thumb tack or tuning up an outdoor 3 meter antenna system. CC requires intensive frequency search and study to avoid interference to licensed stations, especially taking into consideration night time "skywave". Although CC pipes the signal via the power wires into the power socket, radios can still pick up over the air signals from skywave and care must be taken to ensure those stations are not interfered with, as there may be a listener within a CC system's coverage that listens to that station. Something that 219 doesn't really have to worry about because skywave totally wipes out 219 transmissions to the point where consideration of interfering with a station coming in via skywave would be within just a few houses or few hundred feet.
Moral is...don't be intimidated by false premise or persuasion. CC is a highly viable platform and if done right, can work together with a 219 system to form a very effective Part 15 AM station.
I've been involved with CC systems, along side with television and radio engineering for 30+ years and never has any system I have installed or worked with EVER been such a problem as described above in the OP post.
For more information, [email protected]
And someone said I post counterproductive posts? :/
"So, this new interest in Carrier Current doesn't seem to make much sense. Of course, it has been proven to work within its known constraints, but it doesn't sensibly offer expanded range relative to a good single Part 15.219 transmitter installation. In fact, given the typical single-home scenario, it seems to offer a smaller or, at best, equivalent range."
The above statement comes from obvious inexperience..or too much reliance on simulation instead of real world application. But since it's approaching the holiday gift giving time, it in a sense makes sense if one were to read between the lines of a car salesman's pitch.
"This is a technology that goes back to the 1940s.
BZZZZ..WRONG!
CC goes back to the 1920's when early telephone and power companies used CC to communicate to distant power switch stations and early telephone switch hub stations.
"There seems to be perception that Carrier Current offers a way to achieve a much wider coverage area within the confines of the Part 15 rules."
It does, and can. Some CC installations can cover an entire town spanning 4 or 5 miles across and wide, all depending upon how the power grid system is configured in said town or village. Far exceeding the 1 or 2 mile at most 219 system even with an "ultimate" 3 meter antenna system.
And even if the grid system was wired up in such a way that a single CC system would not cover the entire community, multiple CC systems fed through power splitters to multiple couplers comes into play..even feeding leaky coax from those splitters.
Now put a well designed and installed CC system together with a well designed and installed 219 system, single systems or multiple systems, you got one hell of a Part 15 AM station.
RFB
I have a few comments of
my own when I get back.
Best Wishes,
Bruce, W 60 HZ
Good Carrier Current introduction...
http://krocksradioone.com/forum/index.php/board,7.0.html
another good carrier current story...
http://www.gregssandbox.com/wocr/
For my point of view on carrier current I present a boiled down set of opinions and findings, based on having installed and now operating an experimental CC AM radio system.
THE MAIN THING IS THAT ONLY PERSONS WITH SOUND ELECTRICAL/ELECTRONIC BACKGROUNDS SHOULD DARE TO DO ANYTHING MORE THAN CHANGE A FUSE AT THE POWER PANEL WHERE THE RISK OF DEATH IS INCHES AWAY!!
Local electrical service conditions vary so widely that no outcome is ever the same with different CC installs.
My system was unable to get an acceptable match into the power wiring for reasons that are not understood.
By comparison, it turns out that neutral injection works magnificently on my wiring, but this may not be true in someone else's situation.
In most locations within my coverage area the AC hum on the AM carrier is not a problem, except that rotating a radio finds positions where hum increases.
On the western boundary of my coverage area, less than 100' away, there is about a 10' wall of hum where the AM signal is overcome by a buzzing blast.
The eastern extent of the signal is perhaps 1,000' along the power lines fed from my local power transformer up on the pole, with signal strength dropping at each pole along the way, this judging by an auto radio directly along the wire route.
My general coverage area is more or less exactly the same as that from my free-radiate system, which itself will be upgraded when an outdoor antenna is added.
The main comparison between a free-radiate system and a CC system has to do with segments of the medium wave band, where a free-radiate transmitter is most efficient from about 1300 to 1700kHz, whereas a CC system enables efficient use of frequencies 530 to 1300kHz.
Although CC systems can work all the way up to 1700kHz, it would be far more efficient to use free radiance in this upper band, in my opinion.
I love the passion when I read everyone's comments versus CC & free radiate systems. I have no doubt that the SSTran is an amazing product - I have certainly read many many awesome reviews about it. My experience is with the rangemaster (and now talking houses) yet there is a part of me that knows the SSTran is going to be in my stable soon. I can't wait to experiment with it for free radiate.
However, back to CC - with neutral loading there could be some success. if the SSTran was to match, couple and send a dozen or so watts into an AC system, I bet there would be buyers. I know I would scramble to have one. Especially with entry prices for CC being around 1500. Or- how about a hybrid transmitter like I have seen hinted about - something where you could do both - CC and free radiate a beat timed PLL signal to both free radiate & CC.
my whole goal is not to get as much signal as I can legal radiate to as many people as I can. they are all good systems... I hope to integrate them into a great radio station.
Sorry if I stepped on anyone's toes... just thinking maybe everyone can make a ton of money off a great idea while I get what I want as well... a decent broadcast station coupled with a big net stream... to effectively serve this market. I honestly believe that with enough willpower... it will happen.
I am grateful to all of you!
bet RFB could design a good low power CC tuner and CC Transmitter. my guess is for him to do so it would need to made made worth his time and expertise IE: Monetary Compen$ation. you would have to contact him about that though. can't say either way if he would or wouldn't but prototype designs don't come cheap that is for sure.
It has been many years since I worked with CC at a college but it did work as intended, namely to cover the dormitories. There was hum in some receiving locations but in general the signals were usable and hum free. The transmitters involved were tube units and ranged in power from 5 to 25 watts DC input depending on the size of the dorm. and all operated on the same frequency. The signal was barely readable outside the dorms past 50 feet or so and we never heard mutual interference. The only disappointment was the audio quality which was limited by the leased phone lines used to distribute the audio signal. The college couldn't (wouldn't) afford broadcast quality equalized lines.
The programming was provided by students at the College Conservatory of Music and there were listeners as demonstrated by one of our phone-in fund raisers.
Now, to the present. I live in an area where only two houses are served by each transformer so it would seem that CC is not worth it if the signal is blocked by the transformer. Yet RFB reports neutral injection with a separate ground works past the transformers. There is also the possibility to inject into the coax shield of cable TV wiring but this may be risky in that it may interfere with the cable service.
Phil's point about comparative range between CC and a 15.219 optimized system may or may not be valid but the big unknown is how listenable are the two signals within dwellings. It could be that CC would have the advantage because of free wave absorption in building materials or it could suffer from QRM which affects both modes.
It remains to be seen in each installation how well it performs. Beware however that sometimes projects fail because of sub-optimum engineering such as poor matching to the load. My take is we should keep experimenting with CC and gather experience so meaningful discussion can happen.
Neil
" if the SSTran was to match, couple and send a dozen or so watts into an AC system, I bet there would be buyers."
Probably. However, and unfortunately, and according to it's maker, the AMT5K cannot match up to 50 ohms as is, not if said unit is to hit that "sweet spot".
But given a linear amp would be required, at that point who care's about the efficiency of the "exciter" anyway because your not trying to maximize signal transfer from the output elements to the wire antenna.
If the linear has good input sensitivity and appropriate loading, a AMT5K would work driving a linear for a CC system.
But I will let the maker chime in on that one, I'm just giving my opinion based on connecting dozens of different types of low power AM transmitters to linear amps for CC systems.
"Sorry if I stepped on anyone's toes"
You didn't. Only CC was and not by you.
RFB
"There was hum in some receiving locations but in general the signals were usable and hum free. The transmitters involved were tube units and ranged in power from 5 to 25 watts DC input depending on the size of the dorm."
In the hey day of tube based TX's for CC, the couplers used did not have very good isolation nor return AC isolation. Hum was caused by AC energy returning back into the transmitter output element (tube) and would modulate the carrier with that 60 cycle hum.
The couplers TCU-30 and CP-15 couplers are basically a high pass, low notch brick wall tunable filter allowing RF signals from about 130Khz up to 30Mhz to pass through, while brick walling anything below that, including 60 cycle AC. They offer a 3000:1 return isolation ratio, something the old style lump inductor/capacitor couplers could never achieve. Those were a nightmare to keep tuned up as those old time couplers could not self compensate for the wide varying inductance on the lines when load conditions changed. They constantly needed tuning to maintain peak coupling, and quite often they were left alone once tuned up, which is why on some days/hours the system would work well with very little hum and on others the signal would be plagued with hum and other problems.
"Yet RFB reports neutral injection with a separate ground works past the transformers."
Neutral injection does bypass those transformers, allowing the CC signal further down the line. Depending on the size and configuration of the grid, that could mean the signal goes down line a couple blocks or a couple of miles or more.
Don't expect huge down line range in a jammed packed urban setting as those grid systems are so chopped up into small segments your lucky if that signal get's a down line range of a couple of blocks..if even that.
However in a small town, it is a high probability that the grid is not as segmented as it is in a large city, and that CC signal will get several blocks if not the whole town with just one TX and coupler.
The power grid systems are laid out and connected based on the size and population density of the location. With more residents/businesses loading down the grid in a large city, they have to segment it so as to not overload a single main circuit, whereas in a small town, it's not such a burden on the main circuit so the grid won't be as segmented.
And as said even 30 plus years ago with CC systems, it all depends on how that grid system is configured which determines your "millage". This is why in some locations, multiple couplers fed through power splitters and coaxes were used to couple to the next segmented grid and so on.
One thing about CC vs 219 free radiate systems. A CC system is NOT subject to being drowned out by night skywave like 219 free radiate systems are. While a 219's signal get's overtaken by the skywave noise and signals, a CC systems signal remains constant and present on the lines, and will continue to have solid clear coverage even at the tail end of the line.
There are cases where the grid system is so stubborn that a CC system may not be the way to go. Same is true with a 219 system where there may not be adequate access to dirt ground, like an apartment dwelling or hi-rise building, or so much neon sign, AC buzz saw noise a flea signal wouldn't stand a chance even making it down the street let alone a 1/2 mile.
So if comparisons are to be made, then the comparisons should be made on an even keel of equal circumstance, not the one blanket rules all approach.
RFB
"prototype designs don't come cheap that is for sure."
One thing I have discovered when prototyping is the numbers and reality rarely mesh, especially prototyping a CC system. It took me several days to build that small TH coupler after simulating it and crunching numbers for hours, after which only to find that the numbers and simulator was WAY off from reality when it was connected up to the lines.
At that point, it came down to trial and error, as usually does happen with prototyping without super-cray computers and simulator programs that still won't quite fit reality into the calculations, particularly working with a load impedance/inductance that constantly changes.
As to the TX itself, heck any transmitter will do, of any make be it home made or manufactured. It is the coupler that is the nightmare. Look how long it took LPB to design and perfect that TCU coupler from the day LPB came into being! 15 years or thereabouts. Thank goodness for ferrite toroid cores. Those are what made the TCU and CP couplers possible.
RFB
RFB, your comment about the 60 Hz AC getting back into the final is interesting and it is not surprising that this can happen. Though the details have faded in memory I designed and built the 25 watt transmitter the campus used. The output was filtered by means of a B&W L and a series C tuned to the carrier frequency. The signal monitored at the transmitter (with a portable radio) indicated no hum and confirmed the intent of the LC filter which was to pass only the RF. I don't recall that any matching network was used other than the LC filter so the transfer efficiency was probably very low. It makes me wonder where the 25W DC input was going.
The other transmitters were built by other students, usually ham operators or engineering students and these were built before I came on board so I don't know the details. Many years after I left the station received a six figure gift and replaced most of the studio equipment and all the transmitters with commercial units.
Neil
is very important.
When it comes down to actual data, I
really only know a few things:
1) Ground returns are very important
at distances from your transmitter
with Part 15.219.
I was able to make a Part 15.219
installation that could be heard well
1/2 mile to 2 miles out on a good car
radio. But one of the most important
things I found out is that - it was
heard very well in my downtown area,
which is 1/2 miles from my house.
(That's the south edge of downtown.)
Now, that downtown area is at least a
mile wide. In most of the downtown,
the car radio signal would come UP and get louder
near large buildings. I think the
ground returns were better there - hence
the signal increase. As mentioned
before, one friend of mine who did
errands in the downtown area everyday
would listen to my station all over the
place there on his car radio. So I
think there is something to be said
about an increased ground return path
in a downtown area with a lot of
buildings.
2) My neighbors were able to hear my
Part 15.219 on good radios in their
houses 500 to 1000 feet away.
So, despite electrical interference, and such,
a .219 signal will get into houses
in the neighborhood. Granted, the
houses in my neighborhood are close
together.
I was never able to check that further out.
Oh - except, one mile out - a friend
could just barely detect the presence
of my station on a good portable radio
in his living room. Had he gone near
a window, he might have gotten it
clearly, who knows? But anyway -
a 15.219 transmission can penetrate
in houses with 500 to 1000 feet. With
fairly good radios. One radio was an
unknown boombox and the other was a
GE Superadio. (Admittedly, the
Superadio is very sensitive.) That's
all I've learned about that. I wish I
had done more when I could have.
3) You guys know my CC data so far.
This is all just starting for me,
and so is the 13.560 Part 15.225
experiment. Oh yeah - with CC, if
your local area is wired "right"
(luck being with you) your CC signal
might get into those really really
insensitive horribly performing
clock radios because they are plugged
into the AC line. (In some nearby
houses. I believe RFB had a clock
radio reception very very very far
away. But that's his data, and not
mine. I would love to know more
about that.)
Carrier Current experimentation is
also potentially dangerous or lethal.
And we must never ever ever forget
that.
4) A strict Part 15.239 FM set-up
is limited, but I would not rule
it out in some situations. There has been tons
of debate on this. I think FM might
work well in part of an apartment
building. (Your station would have
to be inside the apartment building, though.)
That's all I've learned. Plus I've learned
many things about electronics.
There is so much that needs to be done
and we are all doing it. Better Part 15.219
set-ups, CC, clustered set-ups, repeaters,
WiFi work, etc. Some of these are very
very difficult, and only a few may
have success. But we keep trying. Then,
there is the whole audio processing
issue for Part 15 AM, which I don't understand at all
because I do not have the gear.
I really regret that I am moving and
will probably never again have an
outside .219 AM installation. So
that's why I'm working on a portable
one. And that's another experiment.
Well, anyway, let's keep going!
Bruce, W 60 HZ, X-13, GNAT 90.9, SLUG 88.3
Imagine if there was a device that could...
tune & transmit 15.219
amplify & couple carrier current to the AC line through it's plug
do em both at the same time pre-synced
seems legal to me... and could have range. I wonder if it could pass certification at the FCC inside a weather proof case?
what if it also had a 20 or 30 foot leaky cable to span out for added milliwatts.
all tuned to the same PLL. just plug in a TH unit or other transmitter and go.
I bet the only thing they have to worry about is some of us cowboys who find a way to put the CC watts into an antenna. but it's not like we cant do that any way.
I might have to start a company.
"I bet the only thing they have to worry about is some of us cowboys who find a way to put the CC watts into an antenna. but it's not like we cant do that any way."
Disclaimer: If you do the following..you are responsible.
The TCU and CP couplers can tune up to a monopole over a ground system..even a 3 meter monopole.
No special connections are required except to tie the couplers neutral return to the same ground as the couplers input. Then tie one of the "line" outputs to your monopole, and connect the ground of the coupler to the ground system.
Again, if you do this, only perform very short transmission tests to see how it works. It is experimenting and not intended to broadcast for hours or days as such a setup is highly illegal.
Results: TX TPO 5 watts 1670Khz inductance 32 capacitive bank 1300pF 3 meter monopole over radial system of ten 10 foot long wires laid on surface of ground with 3 meter monopole 1 meter off the ground, coupler at the base (puppy hut). Range was 4 miles solid, 5-6 begins to get noisy, 7 and beyond well into the noise floor. Ground conductivity 15, dry day.
RFB