carrier current is near field wired/wireless. that is to say for the most part if you are within about 50 foot of the line or plugged into the line you get a usable signal level. more than that it dies into the static. cranking the power turns up the near field some but does very little to propagate the signal down the line much further. propagation down that wire depends on how the topography of the electrical grid is laid out. so long as you are within the radiation limits of 221 from any point along that propagated piece of wire (or building where signal is injected) you are legal.
to further expand on the above RFB has a little series posted here on part 15 carrier current and how to do it.
http://krocksradioone.com/forum/index.php/board,7.0.html
best explanation of carrier current you will get.
"carrier current is near field wired/wireless."
Even FCC field agents often forget about that fact, as does many radio dabblers with "years of experience" or professional consultants, to which one would wonder why something so simple of a concept of radio transmission would be so misunderstood by those decades of experienced math manipulators. (haha)
It reminds me of what my math professor told me. Numbers don't mean squat until it meshes with reality, and even then the numbers usually run into a variable to which leads to the "uncertainty principle", or better put...the "I don't know beyond this point thus here is a set stop gap until someone does".
I would take a wild guess and say that the reason for the confusion between a CC system and regular monopole center located radiator producing far field is that those who confuse think the power wiring is a monopole, or will radiate like a monopole. Well it won't, and that has been established long ago by ham's doing CC during WWII, and even long before that when the early telephone companies were using CC to transmit internal communications and control signals to switch stations located in the middle of nowhere.
Another thing some confuse is that just because the TX is running at so many watts, that instantly the operator is violating the rules and the signal is getting out too far, though they ignore that it gets out far DOWN the line, and not FROM the line. Big difference between those two points and something that EVERY radio engineer should already have a good grasp of after elementary radio 101 class..dabbling with crystal radios and wires strung everywhere.
What I have learned about CC comes from information obtained from very old ARRL publications, notes and small articles scattered in libraries (back when information was abundant in libraries), and most of it from actual doing and observation and measuring. Such information, in other fields, would be considered extremely valuable. Some people have a natural knack, or given gift like I do to figure stuff out in their head on the fly without the need of simulators. However here in radio such information seems to be ignored and revert back to the far field concepts, to which that far field concept does not apply at all, and never can. The nature of the utility grid, and it's incredibly low impedance that swings with a ratio that would make ANY monopole system come crashing down and decades of experienced engineers scratch their behinds wondering what the heck, is the reason why CC is NOT measured or set up like a typical monopole far field radiated signal. It never will be, never can be and no matter how much you mush and slush the numbers, a CC system will NEVER produce any far field like that of a monopole system, regardless of input power applied to the coupler.
By the time the coupler matches, isolates and maintains proper loading to the TX, your ERP off that power wire is less than 1/4 watt when driven by 30 watts from the TX. You would need several hundred watts just to get a mile OFF the power wire with far field..oh and in the HORIZONTAL polarization to boot. I don't see any vertical utility wires running anywhere.
There is a source of information besides what little there is on the web. And that is by doing and observing and measuring.
Sort of like what Bruce is doing! Wow! Isn't experimentation and discovery great?!! :p
RFB
The assortment of measuring tools I have been lucky to accumulate have given me the best feel I've had in this CC experience, and I'll list a few observations.
The automobile radio is very revealing when listening to a silent carrier.
In the driveway the silent carrier is so quiet I had to double check to make sure the radio was turned on. My first test was at a mere 1/4Watt which provides a strong near-field signal from house to pole, but after that the signal declines in downward steps, pole by pole.
Driving on the other side of the street going in the opposite direction the car signal already has sputtering, indicating being on the outskirts of the near field.
Driving past about the 3rd or 4th pole down the line the sputtering begins to rise abruptly and in a very short distance beyond that the signal is gone.
Trying the same thing at 1-Watt the indoor near-field measured higher, but the outside silent-carrier test was only very slightly improved at the same distances.
Testing is as much fun as programming, so I think I will view radio programs as "test audio".
Way back in 1990 a radio station ditched their Volumax 4300 and I dragged it home, not needing it at the time, since it is designed to modulate an AM transmitter and back then I was running a recording studio.
Now, out it comes. And I just printed all 33 pages of the manual, which I found online somewhere in 2005 and have saved ever since.
It's a "peak controller".
Once the Volumax is in the audio chain for the carrier current station, an Aphex Compellor will be added and tested, hopefully the combination will provide a wonderful gob of sound.
Previously, somewhere in this thread, RFB approved of the idea of this particular audio chain arrangement.
It sometimes takes me a long time to do what I say I'm going to do.
I've been meaning to say that for five years.
Last night I went to check my
modulation. Lacking a scope at the
moment (it's lent out) I decided to
try a fun experiment.
I think people have done this before.
But I'll mention it anyway. When 1020
CC is running, all the
radios in the house are distorted -
so it's hard to check modulation.
I took my Grundig S-350 out in the back
yard and retransmitted the received audio
back into the house on 88.3 MHz. It was
night, and the S-350 was about 50 feet out
from the house. The signal was not very
strong - in fact other stations on the
channel were there, too. I listened in the
house on 88.3 and adjusted the audio chain
accordingly.
This was a big help. The W 60 HZ set-up sounds
really good now.
Works well.
Bruce, W 60 HZ
Tha Dood in Poca West Virginia, a part 15 man, revealed a clever trick for setting the modulation level for a part 15 station.
He says plug the audio output of an AM radio to the input of a tape deck with VU meters, tune first to a high wattage station and set the input level of the tape deck so the meter peaks at 100%, then tune the AM radio to your station and set the audio level into your transmitter so it matches the level of the big station.
Brilliant idea.
Carl - that modulation monitor trick
is good. I've done that before, and
I will probably be doing it again.
Soon.
Bruce, W 60 HZ
"plug the audio output of an AM radio to the input of a tape deck with VU meters, tune first to a high wattage station and set the input level of the tape deck so the meter peaks at 100%, then tune the AM radio to your station and set the audio level into your transmitter so it matches the level of the big station."
Unfortunately if the AM radio has AGC..which most do, then that AGC is going to muck with the reading on those meters. What is needed for that kind of measuring is a radio with switchable AGC, or one with the AGC disabled.
Using a strong station as a reference will bump the AGC downward, and the indication on the meters will be representing what the AGC circuit is doing to the demodulated signal, same with tuning to your station in it's close proximity to the radio being used to drive the tape deck meters.
RFB
The AGC function of an AM broadcast receiver usually keeps the average r-f carrier voltage ~constant at the AM detector input when stations of different signal strengths are tuned in.
So that would keep the maximum audio output more or less constant for different stations, which is what the VU meters on an audio tape deck would display.
That would give an approximate, relative indication of modulation -- which for most commercial AM broadcast stations rarely is less then +/-98%, or even -98/+125% (except for dead air).
rich has reassured us that it WILL work and will keep us legal.
Green light.
Yeah it will work, but it won't work accurately.
I'm sure Rich knows why the modulation monitors used by licensed broadcasters for AM do not measure the modulation with an active AGC at the detector.
Good thing the FCC doesn't hold Part 15 AM to the strict specifications like that of licensed AM eh?! Let's hope another doesn't either. And the engineers over at VE are trying to figure out how I can make AM C-QUAM deliver 40hz-18khz audio response. Perhaps it has something to do with precise monitor and measuring? :p
RFB
Probably why so many AM sites are generating all that splatter across the band.
Kinda hard to determine what's actually going out when you got a monitor compensating for what's coming in. Duh.
RFB
Kinda hard to determine what's actually going out when you got a monitor compensating for what's coming in.
It doesn't.
The action of the AGC in the linked device affects the amplitudes of the AM sidebands essentially to the same extent that it affects the carrier.
Such performance does NOT change the percentage of modulation of / in the AM waveform demodulated by an AM detector.
Well regardless of what one or two does it, I perform modulation measurements the old fashioned way...the more accurate way and use measuring equipment that doesn't compensate or alter what I am attempting to measure.
Again perhaps is why the band is so splattered with garbage eh...because they are not seeing what is actually going out using a piece of gear that alters that incoming signal and what is riding on it sitting next to the transmitter. Why would you need AGC to compensate for signal degradation or anything else for that matter when your inside the same building as the TX?
I'll stick to the tried and true method. Always have, always will. FCC doesn't mind that either.
RFB