Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives Magazine Sponsor RF Cafe Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Alliance Test Equipment Centric RF Empower RF ISOTEC Reactel RF Connector Technology San Francisco Circuits Anritsu Amplifier Solutions Anatech Electronics Axiom Test Equipment Conduct RF Copper Mountain Technologies Exodus Advanced Communications Innovative Power Products KR Filters LadyBug Technologies Rigol TotalTemp Technologies Werbel Microwave Windfreak Technologies Wireless Telecom Group Withwave RF Cafe Software Resources Vintage Magazines RF Cafe Software WhoIs entry for RF Cafe.com Thank you for visiting RF Cafe!
everythingRF RF & Microwave Parts Database (h1)

RF Electronics Shapes, Stencils for Office, Visio by RF Cafe

Windfreak Technologies Frequency Synthesizers - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low-priced products, all of which I created.

RF Cascade Workbook for Excel

RF & Electronics Symbols for Visio

RF & Electronics Symbols for Office

RF & Electronics Stencils for Visio

RF Workbench

T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads

These Are Available for Free

Espresso Engineering Workbook™

Smith Chart™ for Excel

Crane Aerospace Electronics Microwave Solutions: Space Qualified Passive Products

Bell Telephone Laboratories - The Eye That Never Closes
November 1946 Radio-Craft

November 1946 Radio-Craft

November 1946 Radio Craft Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

The Eye of Sauron - RF Cafe

The Eye of Sauron ... a different kind of eye that never closes ... at least until Frodo tosses his ring into the abyss.

Here is something you probably didn't know. I certainly didn't, but I'm not surprised. As with many advances in electronics and communications, Bell Telephone Laboratories invented the thermistor. According to this infomercial from a 1946 issue of Radio-Craft magazine, the thermistor was developed to adjust the amplification needed in its relay circuits to provide proper signal strength. It monitored the temperature of the output stage to determine the level. Bell claims the device was sensitive to within one millionth of a degree and could "see" the warmth of a man's body a quarter of a mile away on the battlefield (during World War II). As with most things, improvements have been continually in the thermistor in terms of temperature range, stability, accuracy, ruggedness, etc., all while lowering the price as mass production helps amortize production costs across huge volumes.

Bell Telephone Laboratories - The Eye That Never Closes

Bell Telephone Laboratories, November 1946 Radio-Craft - RF CafeYou are looking at a thermistor - a speck of metallic oxide imbedded in a glass bead hardly larger than a pin-head and mounted in a vacuum. The thermistor was developed by Bell Telephone Laboratories to keep an eye on the amplification in long-distance telephone circuits.

When a thermistor is heated, its resistance to electric current changes rapidly. That is its secret. Connected in the output of repeater amplifiers, it heats up as power increases, cools as power decreases. This change in temperature alters the resistance, in turn alters the amplification, and so maintains the desired power level. Current through the wire at the left provides a little heat to compensate for local temperature changes.

Wartime need brought a new use for this device which can detect temperature changes of one-millionth of a degree. Bell Laboratories scientists produced a thermistor which could "see" the warmth of a man's body a quarter of a mile away.

Thermistors are made by Western Electric Company, manufacturing branch of the Bell System. Fundamental work on this tiny device still continues as part of the Laboratories program to keep giving America the finest telephone service in the world.

Bell Telephone Laboratories

Exploring and Inventing, Devising and Perfecting for Continued Improvements and Economies in Telephone Service



Posted March 25, 2022

Bell Telephone Laboratories Infomercials
Crane Aerospace Electronics Microwave Solutions: Space Qualified Passive Products
Amplifier Solutions Corporation (ASC) - RF Cafe

Windfreak Technologies Frequency Synthesizers - RF Cafe

KR Electronics (RF Filters) - RF Cafe