Carrier Current From Scratch

In the past there have been hints about building the kind of extension devices that would allow stock Part 15 transmitters to be utilized for carrier current, but nothing has been done.

Thank you mir for bringing the idea to life with its own thread.

There's another thread right now, about using a 60-Watt RF amplifier as the output connecting a Part 15 transmitter to a carrier current system, so that also relates to this subject.

To the best of my knowledge the type of RF amplifier needed is known as a "linear amplifier", which allows the modulation already applied in the Part 15 100mW transmitter to be carried forward without distortion. Otherwise, you'd need to add a modulation capability to the final stage of the extension amplifier and remove modulation from the Part 15 "exciter." It would get tricky.

As to a coupler, somebody really needs to draw and release a do-it-yourself 50-Ohm to power-line coupler that doesn't "steal" from the existing coupler patents, unless of course permission could be obtained.

I saw the 60 watter discussion, and it really got me thinking.  So; maybe someone who knows amps and part15 stuff could design a 5watt (thats what I used to use) and coupler system?

Is this of any value to our design?  http://teslapress.com/am25.html

I just have never taken that approach, so

I can't say for sure how it would be.  

I never had an AM-25.  Some people 

really like that transmitter in general -

but it has to be modified in order to 

be used, even just for Part 15.  If that

is not done, some components run

very very hot.  Also, the power input

of an AM-25 is too high for Part 15.  

People have said it runs more 

that 100 mW in, when built according

to the instructions.  (Of course for 

CC this would not matter  -  I believe

Neil did a lot of good work getting the

AM-25 to comply with Part 15.219.)

I have heard that any Part 15 transmitter

can be used for carrier current as long as

it can be matched to the load - which is 

the AC line.  I'm think most couplers and 

coupler designs want to see 50 ohms at 

the input - so any transmitter that is used

would have to have 50 ohms (or close to it)

to work.  I have heard that an unmodified

AM-25 wants to see about 25 ohms on the 

output, but I could be wrong about that.

Maybe the modified AM-25 in the article

is closer to 50 ohms - I don't know.  Although

a Part 15 transmitter would be a lot lower in power than

a typical CC transmitter, it could be used as

a starting point if it is matched correctly.  

There are a few more things that I can say

and that will pretty much be the limit of 

my knowledge, but here goes:

I tried building a coupler with RF matching

coils that was isolated from the AC line.  

It worked, but the coils were large and 

were not put in any kind of shielded box.  

So the coil system was radiating a lot 

of RF (which is what you do not want.)

So much RF was coming out of those 

coils, that any radio placed next to the

them would overload, and stop functioning

completely.  So the coil set-up was also

a transmitting antenna, and that's no good.

Some people have built simple isolators with

caps and fuses and that sort of thing.  They would

feed the AC line and have the transmitter running

full power into the other end.  I tried this with my

RC-6A running 5 or 6 watts.  All I got was a gigantic

"motorboating" sound out of the radio.  It did not

work for me at all.  At one point I made a 10 dB

attenuator which took the 5 watts from the RC-6A

and brought it down to 500 milliwatts - so most

of the transmitted power went into the resistor

network.  Since the transmitter was further

isolated - this approach did work to a point.  I fed the

attenuator network into a simple isolating circuit.   The

signal stayed in the power lines, and went

down the street into houses.  But it was

not a very strong signal.  I also found that

signal strength changed as the day went

on.  This was because people were turning

devices connected to the AC line on and off.

and changing the load impedance.  I have heard

that some kind of wide band coupler would

be good, because it would tolerate impedance

changes and still deliver power.  I do not

know how to make such as coupler, but

somebody else might.  

I hope this is helpful.

Bruce, The DOGRADIO Group 

In a way the carrier current realm is open territory for Part 15 exploration, but the danger of messing with electric power lines is logically the reason it isn't promoted more than it is.

I wonder, in the long history of carrier current, whether anyone was put in the hospital or killed because of their attempt to make it work.

The rise in popularity of FM caused the many colleges and universities to abandon carrier current AM because for a long time they were able to get low or high power FM licenses. Only a few schools have retained ownership of their legacy licensed AM stations.

In my experience with AM carrier current, I find it about the same in terms of area covered as radiated Part 15, but other locations are reported to have different experiences.

Many of us lament the vanishment of LPB, the real trail-blazer in serious CC equipment.

The sole supplier now, so far as is known, is Radio Systems, and I tend to believe the high price tag for the equipment reflects two things: 1) there's a small potential market, so they need to mark it up so as to afford offering it; 2) it would be too risky to offer CC equipment to the hobby market, it could backfire in ugly ways when crispy customers turn up.

The publishing of hobby circuits is probably so scarce because it would be hard to come up with a circuit that didn't infringe on the patents held by the existing equipment.

But CC is there and it's legal.

Yeah, there's no question - in CC -

you really have to have been around

the block a whole bunch of times.

That's why I couldn't endorse that article

as a whole (I'm not qualified to do that

anyway) - but there are a lot of things

in that article that are very very interesting.

Heck you know the story of how I fried my

reel to reel tape deck and almost myself 

trying Part 15 radio in about 1969.  Talk about 

danger.  What came out of the AC socket when

I plugged the transmitter in - looked like a 

lightning bolt!  If I had been touching that

reel to reel deck and ground - I might not be

here today to leave these messages.  

By the way - let me know if I tell the same

story too many times.    

Best Wishes,

Bruce, The DOGRADIO Group