Electromagnetic Waves -- Sir Lawrence Bragg -- Royal Institution (Video)

This is a really wonderful video.  I especially liked his presentation on the nature of the EM spectrum, and his use of the centimeter waves to demonstrate wave behaviour.   The two slit experiment was very nice.  Sir Lawrence's presentation on SWR was brilliant.  

Still, you wonder how would all this be done if those waves of Sir Lawrence (and Young, Maxwell and Faraday) were considered to be the photons that they also really are? 

In any case, three cheers for the Royal Institution: https://soldersmoke.blogspot.com/search?q=Royal+Institution  

Basil Mahon is an Author for Us -- He explains Faraday, Maxwell, and Heaviside

 

Armand WA1UQO has sent me two of Basil Mahon's books.  They are both really great.  He is a wonderful writer who has the rare ability to present not only the people who made the discoveries, but also the technical details of the discoveries themselves.  There is so much to learn from Basil Mahon's books.  I put a link to one of them on the column to the right >>>>>>>>>>>>>>>>>>>>>>

I bought his book on Maxwell so I can read it on a long flight our to California.   

PERSONAL:

Born May 26, 1937, in Malta;  married Ann Hardwick (a teacher of chemistry), April 1, 1961; children: Tim, Sara, Danny. Education: Attended Royal Military Academy, Sandhurst, 1955-57; Royal Military College of Science, B.Sc., 1960; Birkbeck College, London, M.Sc., 1971. 

Check out his career: 

British Army, career officer, serving with Royal Electrical and Mechanical Engineers in Germany, Aden, and United Kingdom, 1955-74, retiring as major; Government Statistical Office, civil servant, 1974-96. Consultant and trainer on censuses and statistics, including work for clients in Russia, Estonia, Croatia, and Republic of Georgia.

And his thoughts on writing: 

Basil Mahon on writing: "To me, the joy of writing is simply the chance to give readers the joy of reading—to share one's thoughts and passions with them, hoping to leave them with a feeling of pleasure and well-being. By the time I came to write The Man Who Changed Everything: The Life of James Clerk Maxwell, careers in the army and the civil service had given me plenty of practice in writing instructions—where crispness and clarity were the cardinal virtues—so the big test was to try to hold fast to these qualities and to entertain the reader at the same time."

https://www.encyclopedia.com/arts/educational-magazines/mahon-basil-1937

From the Netherlands, Manu Joseph explains why he loves Mahon and Forbes' book on Faraday and Maxwell: 

Thank you Armand, and thank you Basil Mahon. 

Understanding Maxwell's Equations (video)

And you should also look at the accompanying web site: 

https://www.maxwells-equations.com/m/index.php#maxwells

Writing about the equations, the author notes, "They are formidable to look at - so complicated that most electrical engineers and physicists don't even really know what they mean.  This leads to the reason for this website - an intuitive tutorial of Maxwell's Equations. I will avoid if at all possible the mathematical difficulties that arise, and instead describe what the equations mean. And don't be afraid - the math is so complicated that those who do understand complex vector calculus still cannot apply Maxwell's Equations in anything but the simplest scenarios. For this reason, intuitive knowledge of Maxwell's Equations is far superior than mathematical manipulation-based knowledge. To understand the world, you must understand what equations mean, and not just know mathematical constructs. I believe the accepted methods of teaching electromagnetics and Maxwell's Equations do not produce understanding. And with that, let's say something about these equations." 

Thanks to Armand WA1UQO for sending me the wonderful book about Faraday and Maxwell that put me -- once again -- on the path toward a deeper understanding of their work.  

https://www.amazon.com/Faraday-Maxwell-Electromagnetic-Field-Revolutionized/dp/1633886077/ref=sr_1_1?crid=1ZRPDYCCN9CGA&keywords=Faraday+and+Maxwell+Forbes+Mahon&qid=1690716355&s=books&sprefix=faraday+and+maxwell+forbes+mahon%2Cstripbooks%2C55&sr=1-1

Thanks also to Michael Rainey AA1TJ.  Several years ago he commented that he too wanted to get a better understanding of these equations. 

A Great Lecture on Calculus -- With Discussion of Maxwell

Farhan Takes us Back into the Daylight -- An Analog Rig with a Homebrew Crystal Filter and an LC VFO

 

There is so much radio goodness in this rig and in the blog post that describes it.  Farhan's blog post will keep us busy for a long time.  There is much to learn there.  But perhaps even more important is his larger view of the role of analog circuitry in ham radio.  Here are a couple of excerpts from his introduction: 

 Here is the memo : The analog never died. The world is analog all the way, until you descend into Quantum madness. The antennas are analog, Maxwell died a content, analog man. Our radios, ultimately, are analog machines and we are all analog beasts too. Amateur Radio technology has evolved into the digital domain. However,  it has only made it easier for us to do analog with computers to simulate and print our circuits.  So, it’s time to bid good bye to our Arduinos and Raspberry Pis and build an Analog Radio for ourselves. So let’s see what we can achieve in hindsight, a return to our native land and a rethink of our approaches. The radio is called Daylight Again, a nod to being back at the FDIM in 2022 after a gap of two years. It is named after the Crosby, Stills, Nash and Young’s song that had been humming all the time while put this radio together, emerging after 2 years of lockdown.  This radio that took two days to come together, no actually two years! That’s: parts of it got built and stowed away, thoughts were struck in the shower, questions popped up during early morning cycle rides and notes and circuits were scribbled in the notebook.  I must take the first of many diversion here: I hope you all maintain a notebook. Write down the date and whatever you thought or did on the bench and the result. Nothing is trivial enough to leave out. Wisdom comes to those who write notes.  I started to build this on Saturday the 14th May and I checked into the local SSB net on Monday morning, the 16th May 2022.

AND

Having clean VFO  is the most important way of increasing the dynamic range of your radio. A free running JEFT VFO that has sufficient power and a good Q components, will be unmatched by any synthesized or direct sampling radios. The math is all on the side of the free running VFO. We are talking -150 db/Hz at 10 KHz spacing, by comparison the Si5351 is -125 db/Hz, it is 300 times worse.

That is just part of the intro.  We should all study the rest of Farhan's blog post very carefully and incorporate the wisdom into our new rigs: 

Here is the blog site: 

https://www.vu2ese.com/index.php/2022/08/04/daylight-an-all-analog-radio/

Enough of the darkness.  Step into the daylight my friends. 

James West, Inventor of the Electret Mic, has THE KNACK

 

James West (r) with Gerhard Sessler (l)  Bell Labs 1976

https://hackaday.com/2021/02/17/james-west-began-40-years-at-bell-labs-with-world-changing-microphone-tech/

For many reasons, this is a really nice story.  It is about a kid with The Knack, a kid who, like young James Clerk Maxwell, wanted to understand how things work.   It is also a technology story, the story of the invention of a device very important to us: the electret microphone. (Remember the earlier carbon mics in telephones?  I'll bet more than a few of our readers are guilty of stealing a few of those mics from pay phones.)  And it is a reminder of the benefits of helping kids who might need a mentor... or and Elmer.    

Thanks Hack-A-Day.  And three cheers for James West. 

How Does My Singly Balanced, Two-Diode, Single Transformer Product Detector Really Work?

 

As young James Clerk Maxwell used to say, "What's the go of it?"  and "What's the particular go of it?"

I studied this circuit carefully when I was using it as a balanced modulator in my DSB rigs.  I wrote up my conclusions in my book "SolderSmoke -- Global Adventures in Wireless Electronics." 

BALANCED MODULATOR CONFIGURATION: 

When I was using it as a balanced modulator, I had the RF "carrier" signal going into L1. This RF signal was 7 dbm, enough to switch the diodes on at voltage peaks.  With the "center tap" of L2/L3 grounded for RF, this meant that when the "top" of L2 is negative, the "bottom"  of L3 is positive.  In this situation BOTH D1 and D2 will turn on and conduct. 

When the top of L2 is positive, the bottom of L3 is negative and neither of the diodes is on.  Neither conducts. 

So we have the RF signal turning the diodes on and off at the frequency of the RF signal.  

Audio from the microphone and mic amplifier is sent into the center tap connecting L2 and L3.  The level of this audio is kept low, below the point where is could turn on the diodes.  The center tap IS grounded for RF by the .1uF capacitor, but it is NOT grounded for AF.  That is key to understanding this circuit. 

In essence by turning the two diodes on and off at the rate of the RF signal, the audio signal is facing severe non-linearity through the diodes.  We could say it is alternately being multiplied by 1 and 0.  This non-linearity is what is required for mixing.  We therefor get sum and difference products:  Sidebands.  At this point, Double Sideband.  

The way the transformer is set up means the RF carrier signal is balanced out:  Even when the two diodes conduct, the top of R1 and the bottom of R2 are of equal and opposite polarity, so there is no carrier signal at the junction of R1 and R2 (they are actually a 100 ohm variable resistor that can be adjusted to make SURE they balance out).  So the carrier is suppressed and all that remains are the sidebands:  Suppressed Carrier Double Sideband. 

PRODUCT DETECTOR CONFIGURATION:

What happens when we use this circuit as a product detector in a receiver? Let's assume we are working with a 455 kc IF.   If you run a 454 kc 7 dbm BFO signal into L1, it will turn the diodes on and off as described above.  But you will NOT be able to put the 455 kc IF signal into the center tap of L2/L3 -- that center tap is GROUNDED for 455 kc.   So you will have to run your IF signal into the resistors, and take the audio output from the center tap of L2/L3.   This works.   I tried it in my HA-600A.  But there is a problem: Envelope detection.  

In this arrangement, we are balancing out NOT the 455 kc IF signal, but instead we are balancing out the BFO.  We don't really NEED to balance out the BFO -- it can easily be knocked down in the audio amplifiers, and IT is not responsible for the problematic envelope detection.  We DO need to balance out the IF signal, because if that gets through we can get simultaneous "envelope detection" and product detection.   And believe me,  that does not sound good.

So I tried putting the IF signal into L1, and the BFO signal into the resistors (as shown above).  I took the audio  from the junction of L2/L3.  This seemed work better, with envelope detection greatly reduced. 

BUT WHAT'S THE GO OF IT? 

But how is this circuit mixing in this configuration?   The strong BFO signal is still controlling the diodes, BUT, with the BFO signal coming in through the resistors,  when the top of R1 is positive the bottom of R2 is ALSO positive.  In this situation D1 will conduct but D2 will not.  The IF signal is facing a big non-linearity. This will result in sum and difference frequencies.  The difference frequency will be audio.  But with D1 and D2 turning on and off in a very different way than we saw in the balanced modulator, how does the mixing happen?  

I think the answer comes from the summer 1999 issue of SPRAT, the amazing journal of the G-QRP club.  Leon Williams, VK2DOB wrote an article entitled "CMOS Mixer Experiments."  

Here is Leon's 74HC4066 circuit: 

I think those two gates (3,4,5 and 1,2, 13) are the functional equivalent equivalent of the two diodes in our product detector. In Leon's scheme the VFO is supplying signals of opposite polarity.  Ours is providing only one signal, but the fact that the diodes are reversed means that they act just like the gates in Leon's circuit.  The transformer is almost identical to the one we use in the product detector. 

Let's look at the output from Leon's circuit: 

"VFO A" going high is the equivalent of the BFO going to its positive peak and D1 conducting. 

"VFO B" going high is the equivalent of the BFO signal to its negative peak and D2 conducting. 

Take a ruler, place it vertically across the waveforms and follow the progress at the output as the two signals (RF A and RF B) are alternately let through the gates (or the diodes).  You can see the complex wave form that results.  The dashed line marked Audio Output shows the difference frequency -- the audio.  That is what we sent to to the AF amplifiers. 

One concern remains:   

What happens when the 455 kc IF signal getting to L1 get so strong that IT also starts to turn the diodes on and off?   I think this will result in distortion, and we can see this in LT Spice.  

Here is the output waveform when the If signal at L1 is kept below the level that would turn on the diodes: 

Here you can see it with a much stronger IF signal:  

The output waveform becomes more of a sawtooth. 

How can I prevent this from happening?   I know AGC should help, but the AGC in this receiver doesn't seem to sufficiently knock down very strong incoming signals. 

Does my analysis of these circuits sound right? 

Excellent Video on Maxwell's Equations

Really well-done.  He gets to the essence without getting bogged down in the math. Great graphics too.