It had been a long time since I had built a spark gap transmitter. The first time I was a young boy living on a ranch in the high desert of the Mojave owned by my stepmother. I had been sending and receiving Morse code on and off a good portion of my growing up childhood life using wires, stringing the devices further and further apart to continue to expand the distance between devices and since the distances weren't great, wires were the simplest most expedient transmission method of doing so.
One day my dad bought a brand new, or at least not used, World War II U.S. Army surplus jeep right off the docks in San Francisco for $225.00 cash. He drove it to the ranch and more or less just left it. About that same time I came across a photograph of a war time jeep that had a battery operated radio that could both send and receive with no wires for transmission. Well, we had the jeep, so I figured if I could come up with some sort of transmitting device that ran on batteries, and/or better yet, the jeep battery, I could send Morse code from across the farthest reaches of the ranch from the back of the jeep just like in the photograph.
MY DAD BOUGHT A WWII SURPLUS JEEP OFF THE DOCKS FOR $225 BUCKS.
SAME AS THE SARGE IN THE PHOTO I WANTED TO SEND MORSE CODE TOO
(please click image)
The thing is, at the time, even though my dad was able to buy surplus jeeps, surplus radios were a little beyond my boyhood pocketbook. Even though my stepmother saw to it I had almost everything I ever wanted, she didn't live on the ranch per se' and I only saw her intermittently. So, in between visits I began to research if there was some practical way I could build or make what I needed either inexpensively or with stuff I already had laying around. It wasn't long until I came across what is known as a spark gap transmitter. From my research, along with a little adult supervision, I was eventually able to build and operate a successful spark gap transmitting device, easily sending Morse code clear across the ranch to my brothers with a receiver in the barn.
The adult supervision turned out to be a sort of shade tree mechanic type guy that ran a scroungy looking one man auto repair shop on a side street a couple of blocks off the main street in town. He told me he had been a mechanic and driver for General George S. Patton's Red Ball Express during the war and I was sure he could change a water pump using only a hammer. I stopped by his shop one day on the way home from school to see if had an old ignition coil laying around that was still good that I could have. When I told him I was going to use it to build a spark gap transmitter he said he had built one as a kid in high school years before but he didn't think kids did that sort of thing anymore. He told me to come back in a couple of days and he would have coil for me. When I came back he handed me a brand new coil in a box at no charge, but what he really needed the couple of days for was to look around to find the spark gap transmitter he had built in high school. He eventually found it stashed away in a box at his mother's place. He said if I got a nice clean mounting board I could come by his shop and use his workbench and tools, and using his transmitter as a blueprint, build one just like it. And that's what I did.
I had gone down to the shop to work on the transmitter early one Saturday when about mid morning a brand new shiny Cadillac Fleetwood drove up outside the garage bay doors. The driver got out and came around to open the other side door and out stepped my Stepmother. The mechanic was there in a flash asking what he could do to help and she told him I was her son. By then I was running toward her to give her a big hug with her asking me just what I was doing in such a place. The mechanic was visibly shaken seeing a person of such stature in his shop, easily seeing even the jewelry she had on was probably worth more than he earned in a year, with the suit her driver wore probably costing as much as if not more than he made in a month. She had only just come up to the high desert from Los Angeles and yet to put on her "ranch" clothes when she was told I was in town, so she immediately came looking for me, decidedly curious as to what kind of trouble I was getting into now.
I took her hand and led her to the workbench showing her what I had been doing, she being careful all along the way not to touch anything or be touched by anything. Having no clue as to what I was babbling about, spark gap transmitters and all, she noticed I had been drinking a coke from a bottle and asked if there was any more. The mechanic said there was a coke box out front but before he could make a move she made a slight head gesture toward the driver and he was back within seconds with an ice cold coke for each of us. Sitting down on the tall workbench stool crossing her beautifully suntanned bare legs, wardrobe matched wedged high heels, and bright red toenails, all the while uncharacteristically sipping coke from a bottle, albeit with her pinkie finger pointing out, she slightly leaned toward my transmitter project on the workbench. Recognizing the battery as the power source I began running my fingers along the wires telling how the device created a spark across the gap sending out radio waves and she immediately grasped the concept saying, "Aren't you the little Da Vinci."
With her comment and sitting there in a greasy old auto repair shop drinking a coke out of a bottle, talking with the mechanic and joking I knew everything was OK. Soon she said we should go and as she was getting up she took a business card from her purse and scribbled her signature or initials on the back and handing it to the mechanic told him if he ever found himself in a situation and felt she could help, to call her. On the way out I turned to wave so long to the mechanic and as I did I could see the driver peeling off a brand new hundred dollar bill and handing it to him saying it was for the cokes.
The next time I had any experience with a spark gap transmitter was many years later in the Army. They sent me to a two week two part hands-on workshop or seminar where, after classroom introduction to theory and application, we built and operated our own spark gap transmitters from stuff that could pretty much be just scrounged around for --- and made in the field without using any commercially available or already made tools. In other words, side cutters, screwdrivers and such weren't allowed, so we had to improvise. At the end of the workshop we were all supposed to end up with a viable operative spark gap transmitter, of which I did. Then as a group we shared what we each had done individually to improvise tools and how, that is, what we did, use, or came up with in lieu of screwdrivers, drills, or wire cutters --- or did we implement shortcuts or discover other options. Telegraph keys weren't provided either, so we had to make those from scratch too. Although ignition coils were acceptable, at the end of the seminar we were taught how to make our own induction coils from scratch, along with their application and use as well as learning about devices other than traditional spark gap transmitters that could accomplish the same purpose.
By now most of you have pretty much figured out a spark gap transmitter is a wireless transmission device that has the ability to produce, propagate, radiate, or send out electromagnetic waves, i.e., radio waves. A rather simple bare bones, even crude or primitive device electronically, it's primary function is to send out the dots and dashes of Morse code over some distance without the need for transmission wires. For the most part, operating a spark gap transmitter, because of a host of national and international laws, is considered illegal because of the disruption their signals cause to regularly controlled radio and TV signal transmission
In the above two schematic drawings both show what is called the need or use of an induction coil. Now days, as far as homemade spark gap transmitters are concerned, except for purists, the induction coil has been replaced by a typical and usually readily available standard automotive ignition coil. After the coil the next main item is the spark gap mechanism, sometimes called an oscillator. The spark gap device is termed an oscillator because when the electric pressure at each standing end of the gap becomes great enough to break down the air between them, the electric wave oscillates or vibrates very much as a string of a musical instrument oscillates when struck and the electricity, attempting to complete its journey jumps the gap creating the spark. The so created spark or disruptive discharge that occurs does not in and of itself create radio waves. It excites resonant radio frequency oscillating electric currents in the conductors of the circuit. The conductors in turn radiate the energy in this oscillating current out as high frequency electromagnetic waves, i.e., radio waves, in every direction to a very great distance.
An ordinary Morse telegraphic key is connected in series with a battery and induction coil, as shown in the diagram. When the key is pressed the circuit is opened and closed alternately by the interrupter and a miniature flash of lightning breaks through the insulating air-gap between the oscillator tips. The oscillators are usually adjusted so that not more than an eighth of an inch air-gap separates them. The reason the correct distance adjustment is important is because in wireless telegraphy it has been found that a "fat" spark emits waves of greater intensity than a long, attenuated one.
The coil and attending equipment can be mounted on a base, however for convenience, it is probably best for the hand key to be mounted on a separate base.Together they, with the battery, constitutes the wireless transmitter with the exception of an aerial wire leading upward typically suspended in some fashion outside and another wire, leading from the instrument, connected as a ground with the antenna and ground wires then connected to the oscillators--one on either side.
In the above coil schematic the Input Terminal, or power in from the battery side, the heavier bold wire, is on the left, forming what is called the Primary Coil. The high-voltage Output Terminal is in the center created by the outgoing wire of the Secondary Coil. The low-tension Negative Terminal or ground, is on the right.
Although the end results are the same, because of differences between induction coils and ignition coils --- in that each were designed to serve different purposes --- the wiring for a spark gap transmitter using an ignition coil is slightly different than traditional schematics. In an ignition coil the primary is wound over the secondary, which is wound first. Notice in the ignition coil drawing above that the primary and secondary ignition coil are connected at one end just prior to exiting through the Negative Terminal. Ignition coils are manufactured that way because in a car ignition system, both the primary and secondary coils need to be grounded to the car body. Connecting them together inside the coil container itself is a way of making that possible with only one external connection. Induction coils have a slightly different design.
An induction coil, like an ignition coil, has two wound coils inside, the primary and secondary. In an induction coil primary coils are located inside while the secondary coils located in outer side, so the magnetic field of the primary coils will hit the secondary coil. If the number of turns of the secondary coil is less, the output voltage is decreased. If the number of turns of the secondary coil is greater then the output voltage will increase.
In the ignition coil, as mentioned previously, the secondary coil is located inside the primary coil. The induction of the ignition coil does not occur when there is a current that passes through the ignition coil but occurs when the current in the ignition coil is cut off. The primary coil will issue a magnetic field when electrified. This magnetic field will occur in the outer area due to the position of the primary coil in the outside area. When the electric current is cut off, the magnetic field that was previously formed will collapse, moving rapidly towards the inside The instant and simultaneous movement of the magnetic field will induce secondary coils with stronger results. As a result, the secondary voltage will increase hundreds of times from the 12 volt input to upwards of 25,000 volts or more output. In the meantime the iron core job is to enhance the movement of the magnetic field from the primary coil, maximizing the natural movement of the magnetic field described above to be focused more intently into the secondary coil.
WESTERN UNION STANDARD RADIO TELEGRAPH SIGNAL SET
MORSE CODE, HAND KEYS, AND DA VINCI
THE CODE MAKER, THE ZEN MAKER
SHANGRI-LA, SHAMBHALA, GYANGANJ, BUDDHISM AND ZEN
ON THE RAZOR'S
As to the subject of donations, for those of you who may be interested in doing so as it applies to the gratefulness of my works, I invariably suggest any funds be directed toward THE WOUNDED WARRIOR PROJECT and/or THE AMERICAN RED CROSS.
The opening graphic at the top of the page of a ignition coil spark gap transmitter was graciously provided by long time radio aficionado, educator, and enthusiast John Welsh