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Spark gap transmitter/Marconi receiver - the simplest wireless transceiver

Picture of Spark gap transmitter/Marconi receiver - the simplest wireless transceiver

For me, it is communication that fascinated me and made me study electronics. I always asked myself: how is it possible to send our voices hundreds of miles away without wires? it is this question that encouraged me to study Electrical and Electronics Engineering. The exiting thing about knowledge is that the more you learn, the more you have new questions in mind. Going deeply into electronics generated new questions: how did Marconi send his first wireless message before inventing transistors and amplifiers? it is possible to use only passive components (resistors, capacitors, and inductors) to transmit and receive messages? how? The answer on these questions made me respect a passive component that I had underestimated its importance before: the inductor.

In this project, I am making a homemade spark gap transmitter, along with a coherer based receiver. The coherer is a simple device that detects electromagnetic waves, and used in the early years of wireless communication.

More on the dawn of the wireless technology can be found in the following webpage:

Step 1: The spark gap transmitter

History and science

Spark gap transmitters are the first devices able to transmit Radio Frequency (RF) pulses (actually, damped signals). The first spark gap transmitter was made by the famous scientist Heinrich Rudolf Hertz. Hertz proved experimentally in 1887 the existence of the electromagnetic waves proposed by James Clerk Maxwell at 1865.

The genius scientist Maxwell (also presented the first durable color photograph in 1861) demonstrated theoretically that electric and magnetic fields travel together through space as waves moving at the speed of light. This proposition was left without experimental proof until Hertz' work. Hertz thought that if the electric and magnetic fields travel together, it will be possible to detect the magnetic field of an electric signal generated across the room.

Hertz uses a relay to transform a DC voltage of a battery into an AC voltage. He then uses a high voltage transformer to raise the voltage signal to Kilo-volt values. It is known that the isolation of the air can be broken with high voltage, and it requires 1 KV to break the isolation of a 1 mm air gap. As a result, Hertz generates electric sparks that travel the air gap between the transmitter's spark balls. These electric sparks generate a magnetic field that can be detected from a distance. Hertz detects the magnetic field by placing a ring with a gap in front of the transmitter. The receiver receives the signal and re-generates sparks that jump between the balls of the micrometer air gap of the receiver.

Concerning the Project:

I made this project to encourage my Analog communication systems course students; I believe it is nice to show them a reproduction of the very early experiments done by communication pioneers.

I made the transmitter using the electronics of an electric lighter. This lighter uses the 1.5v of an AA battery to produce sparks that start fire. The electronics of the lighter (actually it is an oscillator) transforms the 1.5 DCV into alternating voltage, then the HV transformer increases the amplitude of the alternating voltage to kilovolt values. The very high amplitude signal breaks the isolation of the air gap producing sparks. The spark gap and the antenna are made of segments of steel ropes.

Another alternative for an easy and simple transmitter is the use of piezo electric spark generator of a lighter.

I was thinking not to show the transmitter here because I am using "new" components to generate the spark. Actually, I was thinking to use the original components used by Hertz and Marconi: a relay interconnected to form an oscillator, and a car ignition coil for the HV transformer. Unfortunately, I didn't find enough time to acquire these components yet. You can find such a transmitter in the following link:

NOTE: to broadcast using different channels, one has to add an LC Band Pass Filter (BPF) that indicates the channel frequency to both the transmitter and the receiver. The channel frequency is equal to the natural frequency (or resonance frequency) of the LC filter: f = 1/(2*pi*sqrt(L*C)). Note that receiving the signal requires that the receiver is tuned on the same channel (it uses the same LC BPF).

1948 Supreme Court ruled in Tesla's favor. These are Tesla's inventions, not Marconi.

abdelrazzac10 (author)  HardlyHumanFX2 years ago

Thank you very much for the important information! Good to know that Tesla was finally recognized.