After reading your post Doggradio 2 I set the dial at 1020 kHz and a very loud, clear, big band theme was playing, followed by Jim Bohannon and his show, probably on KDKA, Pittsburgh, PA. The signal is fading almost totally away, then back in very loud, like rolling crests on the ocean.
I am hoping on one of the fade outs to hear Hartford, Connecticut.
I really enjoy the way you write,
Carl.
One paragraph makes the reader feel
good.
I hope to have some more real data
on this coupling issue soon.
The secondary (AC cord) has been
wrapped around the primary (LC) with
different amounts of turns.
First I started with two turns. That
worked pretty well - but there are so
many variables to consider.
Then I went to
about 8. That didn't work at all.
Then I went to one. Actually one
secondary turn hasn't been as good
as two. However, my data shows that
tine of day is an issue. Things do
not seem to work very well when
people come home at dinner time and
turn on all of their appliances.
(But that's only speculation.)
I also had to move to an outlet on
the other end of the room. That's
a whole other variable.
So it's going to be test test test.
And write down everything. And the
tests will be extremely brief.
Then the whole thing has to be shielded.
But the shielding will effect everything
else.
I am also tinkering with a coil
for the 1690 Part 15.219 transmitter.
It will be like the one I had before, with
many taps. But there will be some kind of
variable section.
Thanks again for the cool message.
Best Wishes,
Bruce, DRS2
When I first reported that our CC transmitter could be heard on the auto radio for a strong 2.5 blocks before dropping into the noise, RFB suggested walking up to a power pole just beyond the signal drop-off point and holding a portable radio against the ground wire, which he estimated would probably reveal that the signal was till following the neutral path into homes further on down.
I was reluctant to do that, because of the time my wife and I took a nice walk to the gasoline station to get a can of gasoline for the power mower. As we walked home we were tailed by a police car that hung back about 150-feet, as a neighbor had "reported" us for carrying gasoline on the public sidewalk. I certainly do not want to be reported for "holding a box against the power pole."
But today while driving I noticed that there are indeed two poles just beyond the signal drop off point, so I ran the car right alongside each pole and bongo! 670 AM surged up just near the ground wires!
"my wife and I took a nice walk to the gasoline station to get a can of gasoline for the power mower. As we walked home we were tailed by a police car that hung back about 150-feet, as a neighbor had "reported" us for carrying gasoline on the public sidewalk. I certainly do not want to be reported for "holding a box against the power pole."
Imagine that. Being reported to police for carrying a gas can from the gas station back home to put into the mower. So watch out everyone...you are a terrorist if you run out of gas and end up walking to the gas station carrying that red gas can with you!! :/
What's next...tattle tale on anyone who eats too many beans and alters the carbon footprint offset for the elites?
Pathetic. So much for home of the brave.
For the pole test, simply pretend your out for a walk sporting your radio to listen to, and go up to the pole and act as if your resting..leaning against the pole to relax.
Unless the American flag came down and the Swastika flag went up, there is no law saying ye cannot rest up against utility pole...or carry a gas can filled with gas to put into your empty gas tank..on a car or power mower.
GET REAL SHEEPLE!!!
"But today while driving I noticed that there are indeed two poles just beyond the signal drop off point, so I ran the car right alongside each pole and bongo! 670 AM surged up just near the ground wires!"
Back on topic...now you understand how a CC system works. And your CC system is doing EXACTLY what it is supposed to be doing, keeping that signal on the line and producing enough inductive field (near) for radios plugged into the grid to pick up the signal past the drop off point.
This is the BIG difference between a 219 setup and 221 setup. There is NO far field beyond that drop off point. It's all inductive, near field EM propagation. Now for the bigger test, go much further past the drop off point, do the same test and see if that signal is still on the wire 4 blocks away, then 5 blocks, 6 and so on.
RFB
The Carrier Current transmitter is in the basement, way over on the other side. Turning it on and turning it off requires a major days trek to go up and down. In the morning I don't mind at all, but at night I would rather not bother.
Somewhere way in the future is a remote control method to turn it off from up here in a convenient location. But I didn't do that today and I won't do it tomorrow.
Last Saturday night 670kHz CC was left ON all night, dead carrier.
My motivation at the present moment for presenting here is the old saw that "one thing leads to another." We already know what the "one thing" is, namely, avoidance of turning off the CC transmitter. What would be the "another"? That's easy. NOT turning it off!
Solution: stay on the air 24-hours a day. What? Oh, no! I'd hate that. Yet, what a relief it would be not to go down there every night.
The lesser of two evils. Just like voting in an election.
I took the coil apart and tightened up
the primary. The I expanded the
secondary from one turn to two, and
coupled it very tightly, tighter than
any windings I did before.
I powered up. Previously, there had
been a HUGE external field off of the
LC coupler. It is now much much weaker.
by a very significant amount. Peaking
the RF was easy. Finding the low
SWR on the transmitter side was not.
I do not have the capability to build
an SWR indicator on the AC line side
as of now. But who knows what the
future holds.
There is no way to measure the results
until tomorrow, when the channel is
quiet.
I am also trying to figure out how
to shield this thing.
That's a whole other ballgame.
Carl, I think RFB and I (and probably
a bunch of other people who are reading
this) will agree that your system is
working correctly.
I haven't heard from my friend about that
commercial coupler. But he's very busy.
I have no problem doing these experiments
until the real coupler comes along. This
is a lot of fun.
Best Wishes,
Bruce, DRS2
I mentioned before that I had made
a crude device to detect my transmitter
RF energy on the AC line. I believe
it works - in that - it shows there is
RF present on the line. It does not
show how the RF got there. So in other
words, it does not tell you that the
CC system is operating correctly. It is
just a very crude indicator.
It is an AC extension cord terminated
in a wall wart. The wall wart is just
a load for the extension cord to feed.
This cord is then wrapped many many times
around the whip antenna of an inexpensive
(cheap) CB/ham field strength meter. It is really
the CC RF coupler operating in reverse.
In both cases, there is no direct connection
to the AC line.
As mentioned before, this meter probably
uses something like a 1N34 diode that
has to get enough RF voltage to turn on.
(Probably about 0.2 or 0.3 volts.)
The energy drives the meter, and hopefully,
causes it to give some kind of indication -
which is supposed to say, "Hey! There's
RF here!"
Granted, only 500 miliwatts is going into
the coupler after the 10 dB attenuator,
which is there to protect the transmitter
final amp tube. But I had some
disappointing observations from this meter.
In my daughter's room upstairs, and in the
actual outlet being fed, there is a
significant reading on the meter (about
one third scale.) However,
as RFB indicated before, this could be just
from RF coupling through the air, because
nothing is shielded.
At the other end of the house, and in the
kitchen, there is a very tiny indication
on the meter that you can barely see.
However, it does take 0.2 or 0.3 volts
to turn on the diode, so some RF is
there. Again, the RF appearing there might
be coupled through the air. And not through
the line at all. I also received a small RF
reading in the cellar. (In all cases, if the
transmitter is turned off, these readings
go away.)
There was no RF indication whatsoever in our
bathroom. (We only have one.) The bathroom
outlet is a GFI, so I'm not sure what that
means. But if there is no RF in our bathroom,
how can it be going down the street or
down the block?
I'm also wondering how my initial test seemed to
go so well. We heard the signal very weakly
around 15 different city blocks the very first
time I put this thing together. It was our
very first trip out in the car. Perhaps
a connection is broken that I can not find
or see.
I'm not complaining. This is a lot of fun.
But I can see that a simple home made CC
coupler is not necessarily a viable project.
However, I'll still get my wife to drive me
around in the morning. Perhaps we will get
some interesting results.
And I'm sure I'll keep tinkering with this thing.
Probably for a long time. I wish we all knew
how those CC 160 kHz FM intercoms work.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
Those just coupled up to the power through capacitors, usually .01uf 3kv ceramics. The ones I have torn apart never had any real matching network to speak of. But there were various makes and coupling approaches.
The earlier results Bruce were indeed from free radiating RF coming off the homemade coupler. Probably a combination of both CC and direct radiation.
Once the homemade coupler is shielded, the task of perfecting the coupler itself will become much easier as the majority of the signal will have but one way to escape..via the secondary winding of the coupler core.
RFB
Hi RFB, thanks for popping in. I
completely agree with everything
you say, but I have a few questions.
I do not have the eyesight to
build big structures out of metal.
And that LC section is pretty big.
The best I can do right now is
probably a big cardboard box wrapped
in lots of aluminum foil. I still
see this as a "science fair" experiment
anyway. And a temporary one.
Then I thought:
Get a good high voltage .01uf cap,
put a low amperage fuse on it, and
then hook it into the hottest RF
section of the LC. (The transmitter
is isolated by the attenuator, so I
don't think it's final RF stage will
have a problem.) Then take the fused
end, and hook it to the neutral wire
of an AC cord. And plug it into the
the AC outlet. (Actually, I would
do this LAST.) Then take the RF ground
from the transmitter, take another good
.01uf cap, and a fuse, put them in the
line, and ground it to an earth ground.
(Maybe you don't need the .01uf and the
fuse in the ground line - but you
would know. You're the real RF
engineer, and I'm just an uneducated
dude.) Would this put more energy into
the AC power line? (Who knows?)
Then I thought, do you need the LC at all?
The transmitter RF final is isolated by
the 10 db attenuator. There might be
more transfer of actual power without
the LC, and the shielding job will be
so much easier because the enclosure
can just be a small metal box.
Those of you out there who are reading
this that we do not know - don't try this
idea mentioned above.
I don't know if it's a good idea yet.
It might be good, might be OK, might be
horrible.
RFB, my friend, do you have any comments
on this?
Best Wishes,
Bruce, DOGGRADIO STUDIO 2
Well the problem I see with coupling in that manner is the lack of proper isolation as well as proper matching. Remember that the attenuator is providing your TX with a constant load of 50 ohms, attenuating the RF power level, but does it convert down to the much lower impedance of the grid?
When inductance changes happen on the line, these inductive changes will be seen by the TX due to lack of isolation from input to output. Your air coupler coil has a better isolation factor than what would be given by a simple capacitor/fuse connection directly to the lines/neutral.
It's worth experimenting with that approach to see the effects of the line changes vs loading and coupling. It would make a very good learning tool!
RFB
I think you said the impedance of the AC
line is something like 0.2 ohms?
For an experiment, if I put a jumper
directly across the output of my attenuator,
and the SWR on the transmit side is still
good, then the transmitter is safe. However,
that does not answer the problem about
power transfer, that's a whole different
animal of course. (And I would be removing
that jumper first before I did anything else.)
OK. I'm going to proceed with the cap/fuse
experiment very slowly. Very slowly. This
house was built in 1931, and I am willing to
bet that some of the AC outlets might be
wired backwards. But I have a tester to
check that.
Thanks RFB. This will be fun, too, which
for me is what it's all about.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2
In most cases the line impedance off the grid (post step-down transformer winding) is usually 2 ohms or so, sometimes a little higher. This impedance is also dependent upon how many homes are tied to that secondary of the step down transformer and loads on each utility drop. I have seen the impedance on some grids lower than 1 ohm, but in most neighborhood situations that impedance is anywhere between 5 and 2 ohms.
Once in a while you get the very strange impedance like Carl encountered. His "hot" sides were showing up as high as 18 ohms! What was even more strange is the coupler was not able to tune out the excess capacitance thus the high vswr. It was not until he coupled to the neutral and ran an isolated ground rod for the return could he tune the system to hit a 1:5:1 vswr.
Remember Bruce, that the coupling methods in the hey day used LC type circuits and tubes for the finals which were far more capable of handling mis-matches than solid state units. There was more room for error in those setups and far less inductive loading on the grids than today.
If after installing the shunt resistor on the output of the attenuator shows the transmitter to still see a consistent load and does not change when removing the shunt resistor or installing it, then the TX will be fine and the attenuator is indeed maintaining the proper impedance to the TX no matter what the output does..next to a direct dead short. This is important to keep a constant load to the TX which in turn helps maximize the coupling efficiency to the grid no matter what changes take place on that grid.
Let us know how it goes!
RFB
This will be a fun experiment.
I will try some resistors in the 2 to
5 ohm range across the attenuator.
Then I will remove the test resistor
and go to the next step if the transmitter
SWR results look good.
And that will be going from the
attenuator right
to the cap/fuse/neutral. For this
experiment, I will not use the LC,
because I just want to observe the
external RF radiation, or lack thereof,
hopefully.
I have to put this together slowly. I
want to get some real good caps for
this, too. Radio Shack may or may not
have the caps I need. I may have to
go somewhere else.
Thanks again, and stand by.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
I have two stories from recent experience, and one of them has to do with carrier current.
But first I must say I am following Doggradio2's CC experiments with great interest. Now that I have CC in my life I will never be without it.
I've described the complaint I have that I must trek down into the far reaches of the basement to shut off 670kHz at the end of the broadcast day, and have already left the carrier on all night which violates my own station policy.
This weekend I went on strike regarding the basement and solved the problem by scheduling programming for 24-hours a day for the whole weekend.
The second story from experience will appear in the AMT5000 Review column.
I have comments for both of you.
First for RFB, a couple of minor
questions. For the .01 uf cap or
caps I need - Radio Shack only has
1 KV disc ceramic types. These cost
about a buck. I was hoping they
would have something made of better
material. I'm making the assumption
that these would be OK for temporary
experimentation, but that something
better would be needed for permanent
use. Also, I've been looking at fuses.
Do you have any kind that you would
recommend?
And for you Carl, I'm very glad your
CC set-up is working so well. I
wish we could figure out some way
to turn on and off your transmitter by
remote control. The LF carrier current
remote controls, or even the radio
controlled remotes would be over loaded
by all of that RF. I know, because
I have both kinds. Either can be used
to turn lamps or appliances on or off,
but they sure don't work when there is
a lot of RF floating around. For instance,
I can use the radio controlled remote to
turn on my CC transmitter, but then I
cannot turn the transmitter off. The
simple receiver is overloaded at that
point, and cannot receive the command
to go off signal.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2