Episode 29: RadaRange

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There is a good chance you have heard the story about the inventor of the microwave standing in front of radar and noticing that the chocolate bar in his pocket had melted.  You probably haven't heard that the event that story was based on occurred more than 70 years ago, or that it wasn't actually a chocolate bar, or that despite growing up in poverty and having almost no formal education the invention of the microwave was among the least important contributions that the inventor of the microwave left to mankind.  Learn the real story on this week's episode of Hang Your Hat.

Show Transcript

Welcome to Hang Your Hat.  This is episode 29: RadaRange

When it is time to pop popcorn, heat a frozen dinner, or warm up leftovers, there is a good chance that you will turn to a kitchen device that wasn’t a part of our parents or grandparents kitchens - the microwave.  The microwave is now a part of over 90% of American kitchens, but how did it get there and where did it start?  On today’s episode of Hang Your Hat I will discuss the birth of the microwave and its unlikely inventor.


Percy LeBaron Spencer was born in 1894 in Howland Maine population just 171, the 2nd child of Jasper and Myrtle Spencer.  He was born into poverty, but I imagine that his parents still oohed and awed over their new bundle of joy, glad to welcome a new member into their happy little family.

Unfortunately, their happiness didn’t last long.  Less than 2 years later Spencer’s father died.  His mother couldn’t afford to keep him and his brother, and Spencer was shipped off to live with his Aunt and Uncle.

We don’t know much about his early life, but I think he must have been a precocious child, exploring his world, figuring out how things work, and asking why often enough to make the most understanding of caregivers nuts.  Then when Spencer was 7, his uncle, his 2nd father, died as well.  

Spencer had to grow up quickly.  When he was only 12 he left school and started working in the local spool mill making wooden spools that thread would be wound on.  He had to help support his Aunt and himself.  He had only an elementary school education.  Most people in Spencer’s situation would have continued to work in the mill until it closed, or they died, but Spencer was different.

When he found out the paper mill was installing electricity he applied to be an installer, despite knowing nothing about electricity.  In the rural town he lived in there was no-one to teach him, but he gathered up all of the reading material he could find on the subject and taught himself.  He was one of only 3 people that were hired to electrify the mill.

In 1912 the Titanic sank and Spencer turned 18.  He had become interested in wireless communication after learning about the wireless operators on the Titanic and joined the Navy so he could explore it further.  He was in the Navy for less than 2 years.  He was discharged early due to a chronic ear disease, but he wasted no time while he was there.  He became an expert on radio technology while he was in the Navy, and used his spare time to teach himself trigonometry, calculus, chemistry, physics, and metallurgy.  He studied every textbook he could get his hands on while standing watch at night.

When he left the Navy he got a job in Boston at the Wireless Specialty Apparatus Company, which designed and manufactured crystal radios.  His bother worked there too.  Both of them had the title “radio electrician.”

The Wireless Specialty Apparatus Company was absorbed by RCA sometime in the 1920’s.  It is not clear if that was the impetus for Spencer leaving the Wireless Specialty Apparatus company, but he started working for Raytheon in 1925.  He again followed his brother who was already working for Raytheon when Spencer made the move.  

Spencer’s brother appears to have left Raytheon soon after Spencer joined the company.  In 1928 he filed a patent for his Spencer Thermostat and started the Spencer Thermostat Company.

Fortunately for quick cooking enthusiasts, Spencer didn’t follow his brother’s lead.  For the next 20 years, he worked at Raytheon on radio and radar systems eventually earning the Distinguished Public Service Award from the US Navy for his important research into magnetrons during World War II.  

In 1940 the British set out on a scientific mission headed by Sir Henry Tizard.  Their goal was to bring a black tin trunk to the United States that was filled with items that were strategically important for the war effort.  Their mission was risky.  If the trunk fell into enemy hands it could have been disastrous for the allies, but the risk turned out to be worth it.

One of the items in the trunk was a cavity magnetron developed by British physicists Henry Boot and John Randall.  It was pivotal in our radar design.

A magnetron is basically a vacuum tube that generates microwaves.  A basic vacuum tube consists of a negatively charged cathode on one side of the tube and a positively charged anode on the other.  The cathode is heated till it is so hot that electrons gain enough energy to escape from the cathode and travel toward the positively charged anode.

In a magnetron, the cathode is in the middle of the tube and the anode is a ring that surrounds the cathode.  But that is not what makes a magnetron special.  The anode also has holes or slots cut in it called resonate cavities.  There is also a powerful magnet under the anode that creates a magnetic field.

Because of the magnetic field when the electrons try to travel from the cathode to the anode they are forced to travel in a curved path around the cathode, and while the electrons are whipping around the cathode they are also passing the cavities in the anode.  The cavities resonate and emit microwave radiation.  The size of the cavities determines the resonate frequency.

You can think of it kind of like blowing through a whistle.  The air that goes straight through the whistle is like the electrons traveling directly between the cathode to the anode.  But some of the air escapes through the hole in the top of the whistle - which is like the groves in the anode.  The air escaping through the top of the whistle resonates at a frequency that creates a sound wave.  In the magnetron the resonate frequency creates microwaves.  

Boot and Randall’s magnetron design was an improvement over previous designs.  Their design was both stronger and more powerful than previous designs, making it possible to install radar in smaller air crafts.

Magnetrons are used in radar systems, and they were extremely important to the war effort during World War II because they were used to find enemy ships, submarines, and planes.  Without radar, military personnel would have to actually visually see the enemy vessel to know where to target their weapons.  

But there was a problem with the magnetron too.  It was very hard to make.  The war effort required 1000s of magnetrons, but each device took a skilled machinist weeks to complete.  They had to be machined out of solid copper, which was both time consuming and wasted a lot of metal.

In 1941 Spencer invented a machine that could mass produce magnetrons for use in radar sets.  His method stamped cross sections of the magnetron out of thin copper and silver solder.  The cross sections were then stacked up into the shape of the magnetron and cooked in a conveyer belt oven until the pieces fused together into a whole magnetron, kind of like a layer cake.  His invention increased the production of magnetrons from 17 per day to 2600 per day.  

He also developed to ways to make the radar sets that the magnetrons were used in sensitive enough to detect German u-boats from fairly high up in the sky.

He eventually racked up over 300 patents and an honorary doctorate from the University of Massachusetts.  He also became a Fellow of the American Academy of Arts and Sciences; a member of the Institute of Radio Engineers, became senior vice president, and a member of the Board of Directors at Raytheon and had a building named after him at Raytheon.  All with almost no formal education.

Then in 1945, Spencer was standing in front of an active radar set at Raytheon and noticed that the candy bar in his pocket had melted.

The myth is that Spencer had a chocolate bar in his pocket and he noticed that it had melted, but noticing that chocolate, which melts at about 90 degrees Fahrenheit, less than body temperature, doesn’t seem like something that would be terribly notable.

According to Spencer’s Grandson George Spencer Jr, Spencer liked to feed squirrels and chipmunks and carried a peanut cluster bar in his pocket to feed the little critters during his lunch break.  It was a melt-resistant peanut cluster bar that Spencer found melted in his pocket that peaked his curiosity.  

Spencer was not the first person that noticed that things melted around radar,  but he was the first that bothered to figure out why.  He was curious about what had happened, so, like any good scientist, he experimented.  First, he put popcorn kernels near the magnetron and watched them all pop - making the very first microwave popcorn.  Then he put an egg in a kettle and positioned the magnetron to direct the microwaves into the hole in the kettle.  The egg ended up exploding in the face of one of Spencer’s coworkers.  

Then Spencer created the first microwave oven.  He connected a high-density electromagnetic field generator to an enclosed metal box that would keep the microwaves from escaping and did further experimentation by placing food in the box and monitoring it’s temperature as the microwaves cooked it.

Spencer and Raytheon filed for the first microwave oven related patent on October 8th, 1945.  It was called a “Method of Treating Foodstuffs.”

In 1947 the first commercial microwave oven hit the market.  It was called the RadaRange.  It was 6 feet tall, weighed 750 pounds and cost $5000 (that is about $45,000 in 2018 dollars).  It also had to be connected to a water line because the magnetron had to water cooled.  It wasn’t a big seller; however one was installed in the galley of the nuclear-powered merchant ship the NS Savannah in 1961 and it remains there now. 

The microwave was introduced to the domestic market in 1955 under license to the Tappan Stove company.  It was a large wall unit that sold for $1295 - or about $12,000 in today’s money.  It also didn’t sell well.  Not only was it super pricey, the average domestic consumer didn’t really know about microwave technology.

In 1967 microwaves finally started to gain a place in American homes.  Amana, a subsidiary of Raytheon produced a smallish Radarange that could fit on a countertop.  It cost $495, about $3700 today, which was relatively affordable - especially when compared to prior offerings.  

In 1970 there were about 40,000 microwaves in US homes - by 1975 there were a million.  By 1986 25% of US homes had a microwave, now that number is around 90%.

However in recent years sales of microwaves have been on a downward trend due to concerns over microwave safety and potential nutritional impacts of microwaving.

If you are not sure if the microwave should have a place in your home be sure to listen to the next episode of Hang Your Hat.


Since starting this show I have been consistently surprised by the history behind the mundane objects in our homes, and microwaves have been no exception.  Who would have guessed that they were the brainchild of a man with an elementary school education, and a direct result of World War II technological innovation?

If you would like to know the backstory behind one of the objects in your home let me know.  I am always looking for a great new story to tell.  

You can drop me a comment on hangyourhatpodcast.com or you can email me at hangyourhatpodcast@gmail.com.  

Hang Your Hat Podcast is a member of Patreon.  If you would like to help support the show please consider becoming a patron by going to Patreon.com/hangyourhat    

If you are not up to becoming a patron but would still like to support the show please leave a review on iTunes or wherever you get your podcasts, or just let a friend know about the show.

And as always, thanks for listening.





Episode 15: The Sun is Gone, but I Have a Light

Light.  It is one of those things that we tend to take for granted until it isn’t available, and then, stumbling around in the dark, the value of light becomes all too clear.  Humans have been figuring out better ways to light our homes for hundreds of years, but in the last 200 years lighting technology has truly advanced, and it all started with the creation of the electric light.

This fortnight's show discusses the history and future of the electric light, the world's oldest working light bulb, Lumens, color temperature, and the coolest lighting event that is going to happen in North America this year, the 2017 Solar Eclipse.

Featured in the Show:

The World's Oldest Working Light Bulb

The Centennial Bulb,  Credit:  Centennialbulb.org

The Centennial Bulb,  Credit:  Centennialbulb.org

The total solar eclipse of 2017's path of totality, stretching from Oregon to South Carolina.  Credit: Michael Zeiler, GreatAmericanEclipse.com

The total solar eclipse of 2017's path of totality, stretching from Oregon to South Carolina.  Credit: Michael Zeiler, GreatAmericanEclipse.com