Do to lack of eyesight, I'm
just going to summarize these.
1) 6 watts @ 50 ohms into .1 uF cap and fuse
to AC line:
Transmitter resonance light went out.
Lot's of RF in radio room. Radio
sputtered and motorboated, although
it could have been the transmitter.
Test quickly shut off.
2) Transmitter connected to 10 dB attenuator:
So 5 or 6 watts into 10 dB attenuator and
500 or 600 mW out of attenuator
and then into AC neutral via cap
and fuse.
Resonance neon light came back on. But -
Transmitter sounded terrible. Very low
modulation. Audio distortion. I realized
ground connection had fallen off.
(Ground connection prior to yesterday was
from ground bus of attenuator to radiator
in room. I realize this is not optimum, but
it's the best I can do now.)
3) This was changed. Ground connection still went
to radiator, but instead was attached to coax
shield at back of transmitter.
Now audio very very good. Probably 90 or
100 percent. Best I've heard with 1971
vacuum tube LPB RC-6A.
Went outside at 10:PM. Near field appears
to be compliant with FCC Part 15.221.
Transmitter audio signal heard
over clutter on frequency 1000 feet down
street in easterly direction. (Next to telephone
poles.)
Transmitter heard at least 1500 feet in westerly
direction next to telephone poles. At one point
signal faded way up about 1000 feet away. Don't
know why.
No coverage on any adjacent streets except for
first telephone poles on a few. So signal
seems to be going down the line covering a
2500 foot line just on my street.
This is the best so far, and impedance matching
network has not been built yet. I have learned
a lot and I feel I will be able to build a coupler
eventually.
Note: Just before they went out of business, LPB
was trying to figure out how to build a coupler
that would adjust for changes in line impedance.
I have some ideas in this area.
Getting somewhere.
(There has been a lot of talk on various boards
about putting the Ramsey AM-25 onto carrier current.
This would include a power increase mod (or mods)
to permit 1 or 2 watts.) Sounds like what the
doctor ordered to me. Maybe somebody will try it.
Best Wishes,
Bruce, W 60 HZ - - 1020 kHz AM CC
Tonight I ran a CC test at 1/4 Watt (250mW) and the signal in the building was 60dB over 5, as I think is the proper way to read an S meter.
What I need to get down on paper is a map showing where the power transformer actually feeds. I am the last house on the west, but the transformer appears to feed lines for quite some distance east to houses on both sides of the street.
Using neutral injection with a dedicated ground rod involved in the system it is unclear to me whether this arrangement is limited to the power lines on my one transformer out on the pole, or whether neutral and associated ground lines also distribute to other power transformers.
What I am trying to say, is that I don't know where to go to grab the key field strength measurements to assure compliance.
Test ending. Shutting off.
Does anybody have any specifics on this?
I guess the theory is that you get a
little power transformer - say 6 volts
or so, and (via variable resistors, fixed
resistors, and maybe a phase forward and
reverse switch) you can cancel out the audio
hum (or lower it) from your CC system.
You take the parts, put them together, and
get the AC potential down to audio line voltage.
Then you feed it into your audio line somewhere
before your CC transmitter. You adjust the
phasing and remove the hum.
This sounds like it could be helpful and fun to build.
Has anybody done this? I feel like I've heard it
before.
By the way, I do not have much of a hum problem here.
Bruce, W 60 HZ - - 1020 AM CC
That should read, "What I think I've seen."
In the carrier current long wave intercoms from Radio Shack the circuits appear to have coupling transformers with a winding that is center tapped in the way that places one side out of phase with the other, probably for hum cancelation.
But in the couplers for the LPB and Radio Systems CP-15 I do not find any phase canceling circuitry. The toroid transformers look like they mainly provide impedance variations, and the capacitor banks provide filtering and further matching.
And now our next episode -
Just when you thought it was OK to
go back into the pool, it's full of RF!
OR
The final solution - really isn't!
Last time as you remember, things with
the CC stuff were looking good.
"Hey Choncey, look at that moose with
the carrier current transmitter. Is he doing
a remote of the game?
I don't know, Edgar. Why don't you
finish pulling your sweater over your head?"
"Why should I do that, Choncey? The game hasn't
started yet."
Oh, I don't know Edgar. Here come
the cheerleaders!
NO OH! SOMETHING WENT WRONG, AND JUST WHEN
HE WAS THINKING OF STARTING DAILY PROGRAMMING
ON 1020.
Putt putt putt (RF feedback) 6AL11 gone crazy?
Stay tuned for our next episode:
THE FINAL REALLY ISN'T - GET THE HAMMER
OR
7 SOLDERING IRONS, BUT NO SOLDER
(sour sound of horn blowing)
A lot of testing. I think the transmitter
is OK. Things had gotten real unstable.
I just couldn't go to sleep. I had to work
on it.
6 watts into the dummy load. Good modulation
now. We'll see. (I was thinking about doing
some REAL (!) programming from 6:AM until sunset.
That way, the old beast would have time to
rest at night. You know, like a daytime only
station.) I had that idea to proceed with programming
because things had gone so well.
So it must be the attenuator/coupler.
ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
"In the carrier current long wave intercoms from Radio Shack the circuits appear to have coupling transformers with a winding that is center tapped in the way that places one side out of phase with the other, probably for hum cancellation."
That's right. Two windings with a center tap serving two purposes...60hz buzz cancellation and coupling.
"But in the couplers for the LPB and Radio Systems CP-15 I do not find any phase canceling circuitry. The toroid transformers look like they mainly provide impedance variations, and the capacitor banks provide filtering and further matching."
That's because the toroid transformers themselves do more than just coupling. They provide that 3000:1 isolation ratio which is what eliminates the hum buckling.
The toroid arrangement is what also provides the nifty isolation from the load and transmitter so that shifts in the load inductance does not affect the loading of the transmitter, or the coupling efficiency.
RFB
"A lot of testing. I think the transmitter is OK. Things had gotten real unstable."
It probably is ok if it's running fine into a dummy load. This leads to question the coupler itself, a home made coupler which most likely does not have enough isolating between TX and the load, thus your seeing those shifts in load characteristics in the TX. Not good.
Such wild shifts can swing things so far off kilt that even that tube TX may get damaged. Tube might be king but I have yet to see a tube that is 100 percent invulnerable. Wide tolerance yes, but invulnerable..no.
Tube are very high impedance devices, thus subject to more outside influence such as loading characteristics that shift. In today's modern world, tubes are only good up to a certain point, then they become pretty darn ridiculous in what is required just to have them glow..much less do actual work.
Keep at it though Bruce...I would focus on the coupler and it's isolation ratio, but also keep in mind that the more you increase the isolation ratio, the more you dampen the coupling efficiency ratio too. Find the balance and work around establishing a "window" of operation with that balance. You will find that you will have to sacrifice one for the other, and vise versa, but you can find that balance between the two and have a workable coupler.
RFB
This is a blast.
I am enjoying it immensely.
I'm going to run the transmitter
through a dummy load all day to
check it. The watt meter will be
on it with the load, and we'll put
music through it.
I'm going to take the coupler apart
and put it back together.
This may take a while.
I have a "ferrite" loopstick antenna
salvaged from a
radio I just took apart. Could I
make a matching transformer from
that and put it in a shielded box?
It's small. I have small shielded
boxes.
You guys, I have to read all of your
notes again.
Thanks again,
Bruce, W 60 HZ
P.S. I have no $$ to spend, so I thought
I would try this just for fun. If I could
get a hold of some torriods I would - but
that's just not possible right now.
The Carrier Current Testing Station is on this morning.
I set the power output as low as possible before cut off and it's so low on the meter in the coupler that I think it's equivalent to a 100mW part 15 transmitter.
Upstairs on the desk the S meter still reads a healthy 60dB over 5, full scale.
The signal analyzer screen shows 38dBm, making my peak equal to the signal I get from a 5kW station located 1-mile away.
My ambition is to be receivable in the area as if I was coming from some far distant town.
I might get together with Bruce MICRO1700 dog leg studio and make up a fictitious town somewhere.
"This is station GWIZ, Gee Wizz, coming from Tent City, Arizona. We broadcast at 980 on the dial, but we've slipped to 970 because of a missing dip switch."
Thank you for all the great comments.
W 60 HZ ODDS AND ENDS DEPT.
Transmitter has been running for
a least 12 hours on the dummy load.
It sounds great. Whew. I'm glad it's
OK.
I have a possible explanation for what
happened last night. This will explain
itself.
I believe this LPB RC-6A was built for
540 to 1000 kHz. I tried to put it onto
1020 kHz, and when I first went to do that,
I had trouble. The tuning coils and caps
are right on the edge. Then, for some unknown
reason I was able to get it working on 1020.
I think the adjustment is very critical, because
it is on the edge. I believe the coil might have
slipped again last night (because I moved the
transmitter to work on it.) When it slipped, I
lost resonance.
There's an other thing. I moved the coupler, too.
It may have a broken connection in it somewhere.
I won't experiment with it again until it's
completely checked out.
I talked to my friend today about that commercial
coupler that he had. I guess the story is that
he can't find it. I sure can't fault him. He
has given me so much old gear from radio stations
that were throwing things out. If he finds the
coupler, fine. Otherwise, I'm content to experiment.
RFB, I remember your kind offer to sell me a coupler.
Someday maybe I'll have some money. It won't be for
a long time. If you end up selling it to somebody
else that will be fine. If you decide to keep it as
a backup, that's fine, too. Meanwhile, my friend will
keep an eye out for the coupler.
I was almost on 970 kHz last night. Actually, I
was, but not for very long. I had a crystal for
970 which I had never tried. Turns out it wouldn't
start. It would kick into oscillation and then die.
Then it would repeat that over and over. It also
ran very very warm, almost hot. Too bad, too. Carl,
970 wasn't as good a channel as 1020, but the
transmitter liked it better. I got good resonance
on the TX neon bulb indicator.
Carl, we could have called ourselves, "The 970 stations."
You and me.
That's it from here.
It's funny, I think I mentioned - I was just about
to go 6:AM til sunset on 1020 CC with programming,
because it seems like a signal was getting out into
the grid pretty far. I guess there's
a lot more to do before that happens.
Bruce, "The 970 that almost was."
This is great because it means
other people are interested in
CC.
I hope it works out well for you.
Best Wishes,
Bruce, W 60 HZ
Sorry if you misunderstood, I posted those links since you mentioned about a coupler. I did at one time have one to sell but that is already gone and the ones I have aren't going anywhere except into service...once I find a location for them that is!
I'm not the seller nor interested in bidding on those things. But your correct, there are others out there interested in CC. Usually when an LPB item shows up at auction..it isn't there for long, and expect quite a good number of bidders going after it/them.
RFB