Does Heinrich Hertz' apparatus include a proper antenna?

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Summary:
Heinrich Hertz built what looks like an antenna for his spark gap generator. Is it?
How close to "antenna" was the metal barbell thing which was part of Heinrich Hertz' apparatus? Did he know in theory how to build a radio but just didn't have the right components to do it?

I know someone around that time referred to the problem of radio in terms of needing proper sustained oscillation instead of the dampening oscillation produced by a spark. Was that someone Hertz himself or some other scientist reacting to Hertz' experiment?

How long did it take spark gap generators to be outlawed after tunable radio was invented? Were the first radios blasted with electrical storm cacophony from all those sparking radiotelegraph stations, or was that never really a problem?

Did the first "real" radio use a crystal or the "Audion" vacuum tube? Different histories conflict on this subject. Is it a question of where one places the threshold of practicality?
 

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  • #2
tech99
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When you say "build a radio" do you mean something which has a DJ and plays music? Well, the telephone was in use at the time of Hertz and its use for entertainment had been tried. Radio was used for Morse code communication in its early years.

I don't think Hertz had a theory how to do it - it was an experimental set up which started as an investigation into dielectrics. His first steps were understanding the spark discharge and its oscillatory nature. The transmitting dipole and loop receiver were proper antennas. Regarding undamped oscillation, this was eventually required so that transmissions would occupy less spectrum and could be modulated with sound, but spark transmitters served well for twenty years. Crystal sets were used on ships during the first years of the 20th century as an alternative to the detectors then in use, which were the coherer and the the magnetic detector, which was like a tape recorder.

When broadcasting started in the 1920s, after the military released frequencies, vacuum tubes or valves could do the job but were initially expensive. You also needed expensive batteries, 120 volt and a 2 volt lead acid cell. People wanted to hear radio programmes and so started once again to use the crystal detector in conjunction with sensitive earphones.

May I mention that Professor David Hughes experimented with sparks, and "loose contacts" as a detector, and was walking around Portland Place in London with a mobile receiver in 1870. https://en.wikipedia.org/wiki/David_Edward_Hughes
 
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  • #3
RE: "Spark discharge is oscillatory": How much oscillation do you get without the Leydon Jar capacitors and other archaic components Hertz used to keep the oscillation going? Or am I misunderstanding that part of the apparatus?

"When you say "build a radio" do you mean something which has a DJ and plays music?"
I was thinking of a more modest "transmits and receives morse code using sustained oscillations on a reasonably specific frequency", but "radio" I admit was awfully ambiguous.

The time between "Hertz" and "these dampened oscillations are for the birds; we need sustained" was much longer than the poorly-written history made it seem. I read about it long ago and have been holding onto some questions. Like the FM question you more than answered it's just been bugging me all this time.

The "crystal sets on ships" you mentioned just detected the dampening spark broadcasts of the spark stations, right? Am I right in thinking that just like my great-uncle's crystal set he built as a kid the signal was very faint? How did the detected pulse get translated into readable Morse code? What apparatus and/or circuitry was between the crystal and the Morse output?

RE: David Edward Hughes: Fascinating! He seems to have been part of the "it's just induction" gang. The way the history played out one has to explicitly be looking for Maxwell's predicted phenomenon or be duped. A lot of inventors who stumbled across radio chalked it up to induction. It makes Maxwell look all the more brilliant for having predicted radio with no experimental apparatus.
 
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tech99
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The high voltage is generated by an induction coil, which is a step-up transformer. The primary is interrupted by a trembler and a Leyden Jar capacitor is connected across the contact to speed up the collapse of the magnetic field and so increase the secondary voltage. The oscillation does not take place in the induction coil but in the spark-antenna circuit. As the secondary voltage rises up, over maybe a millisecond, it slowly charges the antenna circuit to a high voltage. The spark gap is across the antenna, and when it reaches a critical voltage it breaks down, and a spark occurs. The resistance of the gap then falls to about 1 Ohm, so it discharges the antenna voltage and allows damped oscillation in the series tuned antenna circuit. The breakdown of the spark gap takes only picoseconds, so microwave generation is possible. One of the pioneers, Chandra Bose, experimented with 60 GHz waves generated from a spark gap.

With the ships' Morse system, a crystal set would respond to the many sparks per second being produced. Marconi introduced a rapidly rotating interrupter wheel to raise the pitch of the sound. If the ship's detector was a coherer, the receiver had a relay driving a tape printer and a device to tap the coherer after a signal came in, so that arrangement would give a continuous buzz if a signal was present. It is also possible to use a coherer with earphones, in which case it operates like a pair of back-to-back diodes. In such a case ther current must be restricted using a resistor to prevent to coherer "cohering", so to speak.

Unfortunately for Hughes, the Royal Society visited his laboratory and Sir William Crookes concluded that the effects were induction.

I am not certain myself that Maxwell specifically described how an EM wave might be produced, so Hertz was a real pioneer.
 
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