I sort of worry about the
weather you have out there.
The obnoxious weather hasn't
started for us, yet.
There is one thing I like about
it though - although technically
there is no direct correlation,
crummy weather in the spring and
summer is usually followed by
e-skip.
I always get a kick out of E
openings.
I think it is amazing when a semi-local
station gets covered up by a
station that is 1200 miles away,
for an hour or so.
I do not have the time to FM DX like
I used to, be it still is fun
once in a while.
I'm sorry that you have to deal with
that variable weather.
It's also good you didn't get blasted
this time.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2
The severe weather here in the middle of the continent seems to skip around, even in close areas.....
The last time this exact neighborhood was impacted very severely was about 1955 when a funnel ripped right around here and took out the tower of channel 2, which was at the southwest corner of Forest Park. The mangled wreckage was strewn over some apartment houses and parking lots.
The very base of the tower was preserved, it may still be there, as a mounting spot for microwave to the new tower down by the Mississippi in south city.
This particular building has been here since the 1920s, so that funnel must have skimmed by.
Since then the tornadoes have hit x number of miles southwest of here, north of here, northwest of here and a lot of other skips.
My verbal skills are an exaggeration. By that I mean, I may not possess verbal skills of a normal kind. That prefix "ex" always makes me think something is past-tense. For example, an "exaggeration" is a former aggeration; an "example" is a past ample; "excitement is a previous citement; my "explanation", well, you get the idea.
Anyway, I am presently "cited" about the fact that the MICA RF capacitors have officially been ordered from Mouser to convert the carrier current transmitter to mid-band, at 970kHz, a good open frequency where I will spend all retirement.
That's strange, "retirement" has a different prefix: "re." Like doing something a second time. First I was tired, then I retired.
Carl, your last message is a hard act to
follow. I hope you don't have any trouble
with weather over your way. Keep us posted.
OK. Here's my question.
I have a partial understanding of how
to phase out hum on a CC signal.
One friend told me you can take some
AC from a low voltage power transformer,
and put some attenuators on it. When
you get the potential down to about
100 mV with the attenuators - then you can
inject it into your audio line. Somehow,
then the hum will cancel itself out. I suppose
you may have to adjust the level of the
hum you are injecting. I also understand
it is best to try to phase out the 120 Hz
component, and not the 60 Hz. But I don't
understand how the "phasing out" part fits
in. Something seems to be missing here.
This was a quick conversation just in passing.
Do any of you guys have any comments on this?
I have read about this before. If it was on
Part15.US and I'm rehashing it, I apologize.
I just can't seem to find any more info about
it.
Bruce, DOGGRADIO STUDIO 2
Bruce, you have used many of the correct words to discuss the process of eliminating the AC 60 Hz hum and of course 120 Hz hum, etc., but this is one of electronics thorny tricks.
It is thorny because it is simple, but hard to put into words.
My explanation won't help, I hope someone can present it in a better way, a picture could be good....
A toroid transformer or other "matching" type transformer with identical but opposite windings causes the AC side to "phase-out", which also means "cancel," so it cannot back-flow into the audio....
The same method is used in a telephone to separate the incoming signal from the sending signal...
To get more esoteric the same method is used to convert left channel and right channel stereo into L+R / L-R for FM stereo transmission.
Let me look around for a diagram that might help.....
Carrier Current (CC) broadcasting under part 15 deserves equal interest to that of radiant-antenna operation, because of how neatly they complement each other.
Using the baby monitors and home intercoms as an example, part 15 AM transmitters could be easily manufactured for general home use.
Or, a simple add-on to the available part 15 transmitters could be offered, making the equipment interchangeable.
For several days I've been rummaging through CC links located by a Start Page search, and although a few of them are worth visiting, many are dead links. Despite it's great history spanning decades the CC subject is weakly represented on the web.
Especially lacking are circuit data showing how to build couplers.
The method I discussed earlier of using phase-cancelation to eliminate 60 Hz hum is apparently hampered by the fact that electric loads cause the hum to increase and decrease as electric appliances are switched on and off, making the phase-matching very difficult to maintain.
I spent an hour this morning sketching a simplified version of the LPB TCU-30 and realize it does not use the phase-canceling technique, but rather has an elaborate set of transformer/capacitor matching/filtering as a way of tuning for maximum result.
RFB has mentioned operating both CC and radiated signals at the same time, and indeed, using a method described in a manual within the part15.us library, it would indeed be possible to broadcast on the power lines and antenna using the same frequency.
Doing this might pose the problem that the CC field readings would appear to be higher than allowed because of the influence of the radiated version of the signal coming from a 3-meter antenna. In such a situation two parts of the rules would literally collide.
Well, the problem with my experimental
coupling CC set-up was that it was
going into the power line - but it also
was radiating. I haven't given up on
that experiment, but it will be set aside
for the time being. What is nice about
that approach is that - there is no
direct connection to the AC line. I don't
believe the RF radiation was violating FCC
regs, but then again, the thing wasn't
working as it was intended to, either.
This next try WILL be a direct connection
into the AC line. RFB said it would be a
good learning tool, and I'm sure it will be.
This will be coming soon. By the way, I
love listening to the LPB RC-6A transmitter.
I have been running it into the attenuator
and a small antenna. Just enough to cover
the house.
I does sound very good.
This is sort of what you mention - a simple
"add on" to get the transmitter to do
carrier current. Will, it work well?
Who knows? I enjoy the experimenting regardless.
So I will report what happens.
Bruce, DRS2
It's just a prototype.
The first test will be tonight.
Bruce, DRS2
Dear Doggradio Studio 2
As you test your next carrier current experiment I invite all part 15 members everywhere to toast your launch and wish you the very best.
I don't think this coupler is
working either.
However, I tested it at night
when KDKA/1020 was bombing in.
We are almost out of the "critical
hours" time block here in Connecticut.
I'm going to take a radio out and
go around the block.
I'll Be Back!
Bruce, DRS2
Well it seems as if this direct
coupler is working to some degree.
There is the near field, which
tapers off at a reasonable distance -
I believe - to satisfy the FCC regs.
I walked up my street about 1000 feet.
The signal was weak under the power
lines. But in two places where I
held the receiver up to ground wires
on telephone poles, the signal came
in with greater strength. This did
not happen with the previous external
coupler - instead, I just received more
noise. (The power lines are noisy
around here, which doesn't help.)
So this new result with
this second coupler design shows a
small but significant change for the better.
This coupler is just a prototype, but
I think we might be getting somewhere.
I do not have a good ground and the
power into the line is only 1/2 a watt.
One step at a time. If this experiment
gives me further proof that it is
working as it should, I will go see
my neighborhood friends in their home
about 8 houses down the street. I will
have no problem getting in there with
a radio. But I want further proof first
that this is working right - and the
prototype might have to be tweaked. This all
will take time.
Bruce, DRS2
I decided to put a jumper around
the attenuator and run the full
5 watts into the line.
I did this for about 5 seconds.
The SWR reading only went up a
little bit. In the short time
it was running, everything seemed to be OK.
(However, I know there are many
many variables.) The transmitter
seemed to be fine. It was happy with
the low SWR.
The 100 uH RFCs in the coupler are only
rated at 2 watts, hence the five second test.
Under the higher wattage, I don't know if
they would just saturate or be destroyed.
The ratings for the RFCs are specified for
I kHz, in the audio range. I'm not sure
what this means. Also, there are two in
series. I'm not sure what that means, either.
However, in this "high power" 5 watt test that
lasted only 5 seconds, the SWR was very very low,
only slightly higher than it was with the
attenuator in line.
I realize the low SWR might mean nothing, because
there are so many variables.
Still, it was interesting.
Bruce, DOGGRADIO STUDIO 2
In trying that 5 second 5 watts into
the AC line CC test, I may have
put the jumper over the wrong place
in the attenuation network. Meaning
I still had full or partial attenuation -
instead of none at all - which is what
I wanted.
I just can't believe that low SWR could
be true. It's too easy. I must have made
a mistake with the jumper.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2
Where's RFB?
Didn't I say that already?
Bruce, DRS2
My CC coupler that is going directly
into the AC line fooled me.
I thought I had a low SWR, and that
there was a good power transfer.
I couldn't have been more incorrect.
I had decided to briefly put a 5 watt
signal into the line. I previously had a
low SWR reading
because part of the 10 dB attenuator
was connected, and I didn't realize it.
When I took the attenuator completely out,
and tried 5 watts again, I read as much reflected
power as forward power.
An infinite SWR.
The more that I learn the more I realize
what I don't know.
That's OK.
Back to the drawing board!
Bruce, DRS2