Coupling an SSTRAN to the AC Line

[audioguy]

I saw this question posted on another web site, and I thought that some of the readers here might be interested in a discussion on this topic.

I have a solution that might be of interest to casual users. I discovered this quite by accident last winter when it was too cold to work outdoors. I set up my SSTRAN in the living room and connected a 10' wire to it. I didn't immediately have a convenient place to string the antenna wire, so in desperation I just threw it over the top of my 1980s era Zenith TV set. Imagine my surprise when I discovered that this produced a strong signal not only throughout my house but also down to the end of my block! When I turn the corner, the signal dies immediately once I leave the area of the overhead electrical wiring.

How does this work? My older TV has a CRT display. These older sets had an automatic degaussing circuit that is energized each time the set it turned on. There is a large degaussing coil surrounding the picture tube. The antenna wire from the SSTRAN apparently couples the AM signal into this degaussing coil where it is in turn coupled, apparently somewhat efficiently, into the AC line. This works better than you would think! And it does not involve physically connecting anything to the AC line; a potential safety issue.

There are two disadvantages. It is not very enjoyable to watch TV with a wire dangling in front of the picture, so when watching TV I usually throw the wire on the floor temporarily. The second thing I have noticed is that when I turn on the TV, the magnetic field from the degaussing coil is strong enough to physically move the wire from the SSTRAN! That must be a heck of a strong field! So far, I have not observed any damage to the output of the SSTRAN. But I make no promises; so be aware of this possibility if you try it.

 

[darklife]

Another thought that comes to mind is taking your 10' piece of wire antenna and coiling it around a two wire power cord. The cord wouldn't even have to be connected to an appliance. Heck maybe an extension cord would do the trick.

Using capacitors directly inline with the AC really is not all that unsafe if done properly. Using a fuse and doubling the capacitors in case one fails would be a smart idea though.
I have seen some AC couplers that just use a single capacitor to the hot wire and neutral. I wouldn't trust that with any transmitter!

As far as signal distance it's surprising how well a part 15er using the AC line as a leaky antenna can get out as long as the power line transformer isn't right outside of your house.
People say it travels up to the point of the transformer and no further. I don't think that is 100% correct though because some of that signal does seem to get past the transformer, or at least in my experiments.

 

[Ermi Roos]

I live on a long block 0.6 miles long. The normal city block is supposedly 0.1 miles long; and so my "block" is six city bocks long. There is a high-voltage cable from power lines across the street that goes to a transformer, located on a utility pole on my neighbor's property, that supplies electricity to my house and my neigbor's house. I have placed the antenna of a low-power homebrew 160 m ham band test fixture, that is intended to be similar to Part 15 AM transmitter, in parallel with and several feet away from the high-voltage line that supplies my transformer. The antenna is several feet away from the input to the transformer. I used 160 m to give me more flexibility in doing my test (I am licensed).

Carrying a portable radio, I was able to hear my signal (a 1000 Hz tone) under the power lines along the length of my block; but, as the power lines joined with other power lines at right angles at both ends of the block, the signal disappeared. The signal was audible under the power lines, and a few feet to the sides of the power lines. The signal was noisy, probably because of interference from the power lines themselves.

 

[flytrap]

Years ago I had a homeade part 15 transmitter that I made from junk parts and a schematic from a magazine. I noticed that you could connect the antenna wire to the little metal finger rclip next to the "1" key on an old rotery phone and it would put out an impressive signal in the house and the yard. The same effect can be done with a radio by placing the telephone reciever on top or near the radio, it improves reception. At least it does on the old style telephones.

 

[Ermi Roos]

The finger stop on a rotary telephone was a popular place for hobbyists to connect the antenna terminal of a radio receiver. That was the first antenna used to test a crystal set, for example. This is the first time I heard about the finger stop being used for transmitting, however.

 

[audioguy]

Hi Ermi,

Thanks for reporting on your experiments! I am still using my SSTRAN here at home in the manner in which I described. Today, I was able to measure the distance accurately. My range is just shy of 1,000 feet (to the end of my block). Over that entire distance, the signal is quite good on a car radio, and it's usable (though not strong) on a Walkman. We have overhead power lines on my street. As soon as you get more than a few feet away from the last pole, the signal fades out completely! But on my street, it's actually stronger than what I was getting from my elevated Rangemaster (which has temporarily been decommissioned until I can install a ground system for it). Of course, the signal from the Rangemaster went a lot farther, but I'm not sure most people would consider it usable beyond a block or so.

I'm also licensed and used to be active on 160M AM, but lost interest in long winded monologues and the predictable discussions and signal reports. These days I have a lot more fun with my Part 15 peanut whistle than I have had for many years with all of the expensive and high powered (relatively speaking) ham equipment.

 

[carlvanorden]

this is cool experimentation, I've done very similar experiments. The long and short of it is, no matter what you do, you will get signal close and loud, or, nothing. You can play with the tx and find you get a very good far out signal and nothing close. Using the proverbial copper water pipe or outlet ground usually doesn't result in anything but people try it anyway. But, it is cool you posted these things because I have done them all too, and to an extent, they work, albeit not totally.

 

[Tom Wells]

My experiments over the years with powerline and phone line coupling seem to match that of others:
Kinda works in a near field, but not much use for creating real ground wave propogation ( In my situation )
I find that AC line coupling gives too much hum pickup with my own radios on the property, while not a problem for the greater
range of the signal....but too many points of funny cancellations, etc, and not nearly as effective as getting efficient groundwave working.
Where I live now the 240/split 120/10,000v pole transformer is about 200 feet north of me up the alley, so that means my "antenna"
would be a 500' section of 240v/split residential service with about 10,000 branches, all different directions ending up in grounded conduit.
An impossibly complex impedance with a zillion baffles to sop up energy, almost like an RF anechoic chamber.
So no going with that here. If you lived down a long country lane, I suspect the situation would be totally opposite!
Without all the branches to produce conflicting fields, I'd think it could be a useful method for some and worth trying for experiments.
Now, let's NOT go into how you'd convince an examiner that the AC line at an unknown length is not your "antenna",
since your signal passes through them capacitors...

I did not begin to make any real headway in signal efficiency until I began tying as many things as possible (almost) into my RF
common point, in addition to adding such few radials as my property can contain.

Two days I drove past WLS' tower in Tinley Park and noted that there is NO way "complete" radials could be installed there, due to
size/shape of the property. Some of them would be seem to only be half as long (on the SW corner) as would be proper.
I recall an earlier thread where radial effectiveness is one of diminshing returns/costs.
The FIRST radial added does a whole lot, but doesn't or shouldn't create directionality, the second is a big help, and third, and so on, but
adding the 37th radial is only a small incremental improvement. Worth it for a comm station to put in 120 to ensure their installation meets min radiation efficiency, but a bit of overkill for a hobby station.