[SFDXA] Cycles per second: A historical perspective

[Bill]

 From ARRL Contest Update -

Full Article with photos:
http://www.edn.com/electronics-blogs/all-things-measured/4443043/Cycles-per-second--a-historical-perspective

Cycles per second: A historical perspective
chris grachanen <http://www.edn.com/user/chris.grachanen> -November 18, 
2016

Having spent the last 30 years in the metrology/measurement profession, 
I’ve developed a fascination with some of the giants in the field, the 
Electrical Heroes 
<http://www.edn.com/electronics-news/4385860/A-song-for-the-often-unsung-heroes> 
whose shoulders we stand on every day to perform even the simplest of 
measurements such as verifying AC line voltage or determining the 
frequency of a signal.

Because of my electrical-measurement background, I reply on the work of 
such notable persons as Alessandro Volta (1745–1827), Italian inventor 
of the voltaic pile whose namesake defines the unit for electric 
potential (volt) and André-Marie Ampère (1775–1836), French 
mathematician and physicist whose namesake defines the unit for the flow 
rate of electric charge (ampere).

Recently, I had reason to read about another giant in the electrical 
field, Heinrich Rudolf Hertz, a German physicist who was the first 
person to irrefutably prove the existence of electromagnetic waves, the 
foundation for understanding all things wireless as well as 
understanding the behaviors of light.


Hertz was born in 1857 in Hamburg, Germany. He's well known for his many 
contributions to the field of electrodynamics, but by far his greatest 
accomplishment was in proving Maxwell's theory of electromagnetism. 
Maxwell's theory and associated equations, published in 1865, predicted

 1. The existence of electromagnetic waves,
 2. Electromagnetic waves move at the speed of light, and
 3. Light itself was just such a wave.

This remarkable achievement started with a simple experiment involving 
two coils (Riess spirals: spirally wound conductors with metal balls 
connected at each end) suspended in two jars located in close proximity 
to each other (Leyden Jar: stores static electricity between two 
electrodes on the inside and outside of the glass). Hertz noticed that 
upon electrically discharging one of the coils, it would produce a spark 
in the other coil. This phantom phenomenon by which electrical potential 
could pass through the ether intrigued Hertz, who went on to design an 
apparatus in order to better examine and reproduce this phenomenon 
within a controllable laboratory setting.

Hertz's apparatus consisted of an inductorium (Ruhmkorff coil: spark gap 
generator using an electrical transformer to produce high-voltage pulses 
from a low-voltage DC current. Flux changes in the secondary coil are 
produced by cycling on and off current in the primary coil through a 
vibrating mechanical contact (called an interrupter) and 1-m wire pair 
with capacity spheres (used for adjusting circuit resonance) attached at 
the ends of the wires to create a rudimentary dipole antenna. Dipole 
antennas are resonance dependent such that their elements serve as 
resonators, with the current of standing waves flowing back and forth 
between their ends. Dipole elements determine electromagnetic wavelength 
reception (bandwidth). With this apparatus, Hertz produced and received 
high-frequency "Maxwell waves" (electromagnetic radio waves). He went on 
to measure the electric field intensity, polarity and reflection of 
these waves. In doing so, Hertz confirmed that the velocity of these 
waves was equal to the velocity of light. Hertz's experiments showed 
that light and "Maxwell waves" are both forms of electromagnetic 
radiation obeying Maxwell's equations.

Hertz realized the need to numerically describe the different "Maxwell 
waves" created by his apparatus in terms of cyclicality. To this end, 
Hertz normalized the repetitive occurrence of "Maxwell waves" to an 
interval of one second (cycles per second) thereby uniquely discerning 
these waves by frequency. In honor of Hertz's many contributions to the 
field of electrodynamics the General Conference on Weights and Measures 
(CGPM) in 1960 replaced the designation of cycles-per-second with hertz. 
Below is an ad for a Hewlett-Packard 150A, a 10 MC (megacycle) 
oscilloscope that appeared on page 26 of /EDN/'s first issue (May 1956).


*This Hewlett-Packard 150A oscilloscope ad appeared in EDN's first issue.*