RAN Technology

LM386 audio amplifier makes a really good regenerative receiver!


Ham Radio Information 0 Comments 02/25/2019

Demo of simple AM BC receiver breadboard

Posted By: Robert Nickels (ranickels)
Post Date: 02/25/2019

I'm nuts for minimalist solutions...as the wise old engineers would say "It's easy to make a circuit work if there's no limit on parts or cost".    Early television mogul Earl "Mad Man" Muntz fumed about "overengineering" and gained notoriety by snipping out components until the picture or sound stopped working, then told his engineer "Well I guess you have to put that part back In".

But  to my way of thinking, minimalist designs aren't just corner-cutting, and often take advantage of unique capabilities of components or circuits to accomplish a task in an an elegant way.   That's why I was instantly intrigued by a thread on Radioboard about using an LM386 audio amplifier IC as a regenerative AM broadcast band radio.    Here's a link to that site and I suggest reading it to the end as multiple improved circuits and tradeoffs are discussed:   http://theradioboard.com/rb/viewtopic.php?f=4&t=6413&sid=07d79a1d8c3cb46ad619ac2ba35b7502

The LM386 was invented by Ernie Leroy Long at Motorola in 1969. It was originally for part of a fuel injection system for a Ford vehicle and integrates 8 transistors in an 8 pin DIP package that runs from 9 to 12 volts DC.   It has become ubiqitous for low-cost audio amplification in millions of devices from toys to QRP rigs.    Occasionally I've seen deviations from the reference design in the databooks but credit goes to user "Selenium" at Radioboard for being the first to figure out how to introduce regeneration and apply it as a complete AM radio receiver, not just the audio section of one.

Interestingly this wasn't the first application of an audio IC as a regenerative detector - the discussion above included a datasheet for the 1956 vintage Westinghouse WC183 hearing aid amplifier that shows one.   It seems like this idea has been a long time coming!

I think this simple circuit can be the basis of a number of interesting projects - it sure doesn't take much to make one and try it out.   With a high-Q coils many signals should be audible with a minimal antenna (or none) in urban areas.  Current consumption is low enough that battery operation is feasible and loudspeaker volume always beats having to wear a pair of ear-squeezers!

The recenerative circuit was invented by Major Edwin Armstong in 1912 while still an undergraduate at Columbia University and patented in 1914.  While he later went on to develop the superheterodyne receiver and FM, in my view the elegant simplicity of regeneration is his crowning acheivement.

Here is the schematic I used - see the link above for other variations and feel free to experiment:


    In his book "In Touch with Leo", the success and growing backlog of CB-100 orders is what drove Leo to his banker, Lou Ross, who asked him why he didn't anticipate the number of orders and required capital.  Leo responded "Lou, never on God's green earth could I have believed such an influx of orders!".    More funding was needed than the bank ...  READ MORE
- Robert Nickels (ranickels),  03/18/2019 
  

Spectral Purity using Epson Programmable Oscillators

Do harmonics matter if there's no way for them to be heard?
Category: Crystal Replacement
 In the 5 or so years I've been using the Epson oscillators I've looked at the spectral output many times.   Without a doubt the harmonic output from the Epson oscillator is high as would be expected  from a square wave device.   The question to me has always been "does it matter"?PLL controlled digital oscillators have long been used as LOs in recei...  READ MORE
- Robert Nickels (ranickels),  03/12/2019 
  

The Foxhole Radio

aka "Razor Blade and Safety Pin Radio"...from the Boy's Fun Book
Category: Vintage Radio
 When I was a kid, my dad gave me a thin hardcover book called "Boys Fun Book - Things to Make and Do".   It was printed during WWII on very thin paper as a wartime conservation measure, but was chock-full of interesting projects, ranging from hobbies and magic tricks to sports, puzzles, camping...and the chapter I was drawn to:  "Unusual Radios You Can Build You...  READ MORE
- Robert Nickels (ranickels),  03/08/2019 
   As anyone who likes building radios knows, it's getting harder and harder to buy RF components.   One of the last casualties was the 3-section pi-wound RF chokes made by Hammond, a company that has done more than most to support the vintage radio and audio hobbies.    The Toko variable inductors long favored by QRP enthuisiasts have become all but unavailable, and vari...  READ MORE
- Robert Nickels (ranickels),  03/02/2019 
   The following obituary appeared in the Freeport Journal-Standard on Febr. 9, 2019.      I attended a lecture by Mr. Anderson in the late 1990s after moving to Freeport and working for Honeywell where despite being a supplier to DEC, few realized the local connection existed to the founder of what once was the second-largest computer company in the world.   Mr. Anderso...  READ MORE
- Robert Nickels (ranickels),  02/09/2019 
  

The Case of the Phantom Voltage

“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”
Category: Technical
A Heathkit HW-12 gave me a troubleshooting challenge the likes of which I've not seen before - or even heard of!A few days ago the transmitter wouldn't produce output, and in checking voltages and I measured -75 volts on the ALC line which should be -20.   But it corrected itself and I figured it must have been a solder splash or something that cleared by itself.  That theor...  READ MORE
- Robert Nickels (ranickels),  02/08/2019 
  

The Solvay Conference, 1927

The Smartest Photograph Ever Take
Category: Historic
The Solvay Conference, founded by the Belgian industrialist Ernest Solvay in 1912, was considered a turning point in the world of physics. Located in Brussels, the conferences were devoted to outstanding preeminent open problems in both physics and chemistry. The most famous conference was the October 1927 Fifth Solvay International Conference on Electrons and Photons, where the world’s most...  READ MORE
- Robert Nickels (ranickels),  12/27/2018 
   Put yourself in 1963...A stamp was a nickel, bread was 22 cents a loaf, and you could buy 3 gallons of gas for a buck.   The average wage in the US was $84 a week.  If you were a ham, you might have been able to build and trade your way up to a really nice AM/CW station - maybe a Valiant or DX-100 transmitter with an NC-300 or HQ-170 receiver - a huge improvement over the S-38 you s...  READ MORE
- Robert Nickels (ranickels),  12/17/2018 
  

Astro...Don Stoner's legacy

How many of these rare transceivers have you seen?
Category: Vintage Ham Radio
A recent post on the Cubic-Astro mail reflector noted the similarities between the rare CIR Astro 200 and the much more common Cubic Astro 150 transceivers.   And therein lies an  interesting story...I have done a little research on the CIR Astro 200, and the commenter was right - it is the progenitor of the Astro line we are much more familiar with as a result of Swan (already owne...  READ MORE
- Robert Nickels (ranickels),  12/09/2018 
  

The DX-60 Family

what hath Benton Harbor wrought?
Category: Vintage Ham Radio
When an engineer at Heathkit in 1962 turned his attention to designing a replacement for the somewhat flawed DX-40 novice transmitter, little would he have expected the DX-60 to remain in the Heathkit catalog for 14 years.    From the new solid-state power supply to the streamlined apeperance and dependable performace, the new transmitter was instantly popular with novices who had t...  READ MORE
- Robert Nickels (ranickels),  12/09/2018 

VIEW Video Item

WWII Command Set radio checkout in a P-47 Thunderbolt

Radio Mechanic Jones...bring your screwdriver, you have a lot of Dzus fasteners in your future!
VIEW Video Item

Ham Radio and Disaster Preparedness

A California ham's vintage radios featured in EMCOMM video
VIEW Video Item

Controlling external devices using VERSA-TR

VERSA-TR can be used as an RF-actuated switch to control external devices such as a linear amplifier.
VIEW Video Item

Panadaptor with VERSA-TR

Add big rig features like panoramic/waterfall display and DSP audio with muting using the VERSA-TR

VIEW News Item

Making A Transistor Radio

in memory of Rev. George Dobbs G3RJV (SK)
VIEW News Item

Take the Boatanchor Survey!

Let authors and organizers know what you're interested in
VIEW News Item

Announcing the VERSA-TR (as seen in Dec. 2018 QST)

A Versatile T/R solution for SDRs and vintage radios
VIEW News Item

Mike Beachy N8ECR - SK

"If there's a ham radio heaven, they've got a hell of a net control operator"
VIEW News Item

Rev. George Dobbs G3RJV, SK

"Mister QRP" to many, a sad loss for the homebrewing and QRP community
VIEW News Item

The Coolest Rig in the World!

(this week...or until I say otherwise!)