Well, your words are very kind and
always good to hear!
The signal on the car radio IS weak.
It sounds like the old DOGGRADIO 1690
Part 15.219 100mW DC in, 3 meter stick -
as heard a mile or two away. And our
car radio is very sensitive, so I wonder
if a regular portable radio under the
power lines would even hear the transmission.
This does make me think that I am
probably not violating the RF field strength
formula/regulation for the power lines.
Then my mind still has to grasp the
fact that, in the houses, at the A.C.
outlets, the signal will be strong
enough to listen to clearly.
I will eventually get into a friend's
house on the grid to check. But these
people have busy lives, and even though
they know I am a real radio guy, and
not a crazy nut, this will still have
to be done in a low key way.
Thanks again, Carl and best wishes,
Bruce, DRS 2
P.S. And you're right about relating to
other people about this thing. Nobody
understands it. But my wife was kind
enough to drive me around. (Then again,
i don't completely understand it either.)
Interesting idea Neil. I may consider doing that and submit it for entry in the resource library.
The newest CC system/experiment...let's not get too ahead of things just yet.
Once the LC/Coupler circuit is enclosed and shielded and checked for RF leakage, it cannot be ruled out that it's acting like a transmitting loop with some coupling going into the AC lines via the extension cord. Adding the system's location (upstairs) could also add to the results your getting.
The only ground involved here is the TX ground potential tied to the radiator. It won't radiate, but could be getting strong near field induction from the LC loop and embedding the signal onto that and other pipes within the home, in turn making them radiate.
It's too early to really tell how well the custom coupler is actually doing it's thing while it is in the open, unshielded and with no SWR bridge across the output. So far the primary of the LC is tuning up ok with low VSWR, and that is good for the TX's sake in seeing a constant load impedance. But that could change a little with more or less inductive coupling on the secondary..ie more wraps of the extension cord around the form, or less wraps.
In all I believe your experiencing a little of both CC and emission right off the LC loop itself, and a third effect, the strong near field inductive coupling to nearby wiring and/or piping coming off the LC loop since it is unshielded.
Your on the right track. Conduct the tests again after enclosing the custom coupler and moving the system to where you intend to have it for normal operations. As Carl found out, being away from the breaker panel didn't work out too well until moving the whole setup right next to it. And you will want to be right at the breaker panel so as to make the coupling link (extension cord wrapped around the LC form) to be as short as possible to maximize the coupling onto the grid lines.
Another thing to remember is CC is an inductive system and works with the near field and very little far field. It takes less than a half watt ERP off the grid to obtain the needed near field strength to make the CC system viable. Since the grid lines are very low impedance, and since the CC system relies on inductive coupling onto the grid lines, it takes a little RF power to get to that half watt ERP off the grid lines. Depending upon the overall load factors on the grid lines, and it's load impedance, often only a watt or two up to 5 or 10 watts (TX RF output) is sufficient for an effective CC system.
Also remember the goal is NOT obtaining a long far field!!! 15.221 does not allow for a long distance far field!!! CC systems are not measured in the far field!!! If the CC system is working properly, that signal will drop like flies at the 157000/F distance, which is the noise floor or 15uV. This is not easy to measure when you have a cluster of power grid lines at every half block or full block. But the signal will not fade gradually, or linearly with increased distance from the lines. It should drop suddenly, like hitting a brick wall.
RFB
Within my limited experience, everything you
are saying makes sense to me.
I will check your formula with the near field
"RF falloff" and see what's up there. If I
am not understanding - just bear with me.
I will do the checks regarding the formula
and Part 15.221. (My eyes are not cooperating,
so I have to keep reading this stuff over
and over.)
I agree with everything that you say I need
to do. It will not be easy to get close to
the breaker panel - it is right behind the
furnace. But I'll see what I can accomplish.
This is really foreign to me. I'm glad (and I'm
sure a lot of other people are also) that you
are here!
Now I'm going to step back and take a good long
hard look at this thing - and reread your posts -
and a bunch of other related information.
I can't thank you enough!
Bruce, DOGGRADIO STUDIO 2
I just read your last post again.
I think I'm getting the idea now.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2
A good way to determine the drop off point is to use a small 9 volt powered AM radio and move away from the line till you reach your 157k/F point. At about 15 feet before reaching that distance point the signal should begin it's change from near field to far field. Around 8 feet it will seem like picking up a 219 stick with an 80/20 signal to noise ratio (aprox) and drop sharply as you approach the distance point.
Ex: TX Freq-710Khz
157k/710=221 feet aprox. drop off start 216
(meter formula)47715/F
47715/710=67 meters aprox. drop off start 65 meters
RFB
From what you say, I don't think
I was that far off the mark regarding
the transition from near to far field.
As far as distance from the transmitter
is concerned. Of course, without measuring
the distance exactly it's hard to really
know for sure. But the change over point
from near field to far field isn't drastically
off, anyway.
BUT SOMETHING BROKE AND IT DOESN'T WORK
ANYMORE. RF and SWR readings are off, and
the LC won't peak.
No matter. It's an experiment and I'm having
fun anyway.
I hope I can get it back to the way it was before.
Then we'll go on from there.
I can't really see the words on this laptop I'm on -
but I'll be back.
Best Wishes, Bruce, DRS2
I still can't believe it worked
in the first place. (Or - worked
as well or poorly as it did.)
How could we jump all at once from everything working beyond expectations to something being broken and not working anymore?
There must be an in-between moment when something happened that might explain the change, like Hoover the dog chewing on the LC or the neighbor from clear channel doing a jamming signal.
Give us a theory to work with.
Hi RFB! We'll I'll have to
take the whole thing apart
and start over, in order to
trouble shoot it, but again,
to me this is all fun!
I used your formula for 1020 kHz.
The distance came out to about
150 feet for the near field.
Conveniently, the property
lots on my street are about 75 feet
wide. So, looking back at walking
out of the house with a radio a
couple days ago - I'm trying to
remember when the strength fell off
like a cliff. I do think it was
before 150 feet, based on the width
of the properties as I walked down
the sidewalk.
This is a very cool experiment.
Best Wishes,
Bruce, DRS2
Hi Guys!
I took the experimental carrier current
coupler apart and put it back together
again.
It is working now.
There is a field coming off of the coil.
RFB is right. This cannot be used unless
it is near the breaker box and shielded.
Now I know why people look for commercial
couplers. If you can get one, it's just
plain easier to plug it in and have it
work.
However, I am still drawn to this experiment
like a magnet. I find it to be very interesting
and I am learning more. Learning more about
RF and RF circuits. As someone who was never
a real RF engineer, there is a lot of interesting
radio theory coming together in my head.
Yup, it is still a lot of fun. I might build another
10 dB pad (or more) and put it in the
line. That way the
power going into the coupler will
only be 50 mW (or less)
That will probably pass the field strength regs
for the near field. Then I can just observe
and experiment, and figure out how to shield
this thing. (And listen to this wonderful
antique transmitter in the house without
worrying about being in violation.)
The experiment in it's present form is over. It
cannot be used this way.
Bruce, DRS2
Your experiment was exactly what a good experiment is.....informative and instructional..... you have learned from it and can now plan a better experiment, Doggstudio2.
Because I am getting such good results from only 2-Watts, I am not surprised that you are finding it necessary to dump much of your Wattage.
What I suspect is that LPB and now Radio Systems found that having a variable power transmitter is necessary to deal with the extreme variation of results from different power-line situations.
On the one hand it seems undesirable to change a legacy device such as your 6-Watt transmitter, but on the other hand modifying it with variable power makes a lot of sense, and perhaps you could engage Mr. RFB to design the modification.
There is a modification for the RC-6A to have variable power. I just can't remember certain specifics, but it involved adding a variable biasing voltage somewhere in the final circuit. I had the notes to the modification and circuit diagram and circuit modifications on the stock unit. Unfortunately those notes cannot be found.
A schematic of the RC-6A would be helpful. Again unfortunate that I no longer have the manual and schematic to the RC-6A either. TIS what happens when you move several times across several states and cities over a 35 year period!
RFB
I'm on my daughter's laptop, which
I can barely see, because the screen
is too small, even if I wear magnifying
goggles. I cannot get the mag
software to run.
I appreciate your input, RFB and Carl!
I'll be back here from the "nice big"
computer later on. My wife is watching
TV shows on it. (She works really hard
and deserves to watch fer stuff.)
As you know, the Doggradio computer went
down.
So thsnnkd you guyd snf I'll be back as
soon as I can.
Best wishes
Bruce, drs2
"What I suspect is that LPB and now Radio Systems found that having a variable power transmitter is necessary to deal with the extreme variation of results from different power-line situations."
You are correct. In early CC history and for the typical setup situations (dorms etc), and because of the less than optimum coupling techniques and gear around at that time, power level adjustment was not really an issue. But with the far better couplers it became clear that power adjustment was needed to ensure compliance as well as prevent close proximity receiver saturation issues.
As you have discovered, it does not take a whole lot of power to get the signal down the line. It is a balancing act between good coverage and prevention of receiver saturation and interference issues, thus without the ability to adjust that power level, the balancing act would be impossible.
RFB
We'll, all I can say about these
makeshift carrier current experiments
is that - in the few days I ran this
experimental setup - I had one of
the most wonderful and perplexing
experiences I've ever had in Part 15
radio or any radio for that matter.
(B.R.O.S. - Big Run On Sentence.)
There is no way to get any meaningful
data unless the experimental set-up
is shielded. Also, it had been moved
around on the test bench, and that might
have changed the results, too.
I do not have the eyesight to go poking
around inside the RC-6A unit. (At least
not right now.) But building attenuators
is easy. Even I can do that.
I am not done with this thing, but I am
at a temporary wall now.
RFB and Carl - thanks for all of the great
comments!
Bruce, DRS2
Hi Guys:
As you know, I've been experimenting
with carrier current. I have been
using a 1971 LPB RC-6A transmitter
and a homemade coupler that couples -
but doesn't have a direct connection
to the power line.
These experiments will continue when I
can shield the homemade experimental
coupler.
A great friend here in town who is a
broadcast engineer has a commercial
coupler. He will be lending it to
me probably in the not too distant
future.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2