Field Day with Farhan, his Family and an sBITX Near Hyderabad, India

Farhan and his son Rayyan with an sBITX

The SolderSmoke crew thought it had a tough time this Field Day:  Pete N6QW had hoped to do something, but was stymied by hot California weather.  Dean KK4DAS had even worse weather.  Bill HI7/N2CQR was at a remote QTH with an HW-8 and a wire antenna -- he managed just ONE contact (W7RN in Nevada on 15 CW).  But none of us had as much trouble as our friend Farhan had.   In  his account of Field Day in Hyderabad, we see an intrepid ham standing up against the slings and arrows of outrageous fortune that Field Day often throws at true radio amateurs.  Here is Farhan's Field Day story: 

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You asked for it, so here it goes...

I got the chance last evening to head out to our farmland. My daughter Ramsha had her friend were over. By the time we all got into the SUV, it was already 5:30 pm. I had loaded in the Spiderbeam fiberglass pole, the sbitx with LiPo battery and an EFHW ATU strapped on, into the back into my backpack,  the toolbox with a few hand tools.

On the way to the farm, rain begin to come down. Rayyan (son, VU3ECQ) started said as much, I turned up the volume on Bruno Mars...

By the time we got to the farm, the rain was over(Ha!). We immediately begin to set up the antenna. I chose an inverted V config for the antenna and to use a tree as the support. The spiderbeam, as any who has been taken in by it knows, is a telescoping 33 feet high mast made of fiberglass. A curious villager decided to help us too. The girls had already taken off to pick the Mulberries.

So, Rayyan, the curious fellow, and I tried to telescope out the mast. The curious fellow, having never read the manual, picked up the mast from the wrong end and all the pieces fall out the other end. (Censored @#$%...). Within 15 minutes, we had all the pieces put back in the order of their thicknesses. I scotchtaped the center of the 66 feet wire to tip of the mast and we all hauled it up vertical. For those who don't forget maths, you can figure that two section of 66 feet wire will be exactly 33 feet high and when you tie this to the high end of a 33 feet high pole -- they just hang down vertically in a straight line. I was trying hard to remember the math teacher's name when the telescoping mast decided to untelescope into a 5 feet, collapsed height. My son commented that it has worked as advertised. Now, I wanted to remember my son's Moral Lessons teacher's name...

Next, we scotch taped the center of the 66 feet wire to approximately 2/3rd height. The curious guy and I walked it up back and took it to the tree. Rather we tried to. The branches kept getting in the way. Finally, managed to get within 4 feet of the trunk and I declared that we could just tie it up with the packing nylon rope bundle we were carrying. We did and it held up. 

By now, the two ends of wire had gotten all twisted around each other. We all had an excellent arm workout trying unwind them. The techniques -- never mentioned in any antenna handbook -- is to hold both ends of the twisted pair in one hand each, spread out your arms and make overhead sweeping motion to flick one wire over the other. This method only adds more twists into the wire. I discovered that wires could be twisted around each other both ways. There is no untwisting them. I discovered this amazing feature!

After watching us for 10 minutes, Humera, my XYL, asked us to forgive the world and bring down the mast and untangle the wires on the ground. By now, a stray cow had also sauntered in on her way back home. I think our language attracted her. She was bellowing for her calf to come and watch.

Next, we, efficiently undid the wire twists. Rayyan and the curious fellow held the two ends away from each other and I raised the mast. Or rather I tried to. At 45 degree tilt, the mast sections add up huge amount of weight. I was tottering around with it when it thankfully  leaned onto the tree branches. At this time, I declared it done. We tied the mast at 6 feet height by the rope to the tree trunk. One end went to the a branch of a bush and the other we walked to the point where it was taunt and touched the ground. 

I brought out the radio, much to the curious fellow's surprised, who was looking forward to me doing more entertaining things with the mast rather than a radio. We switched it on, I quickly peaked the ATU to maximum noise and keyed up. The sbitx shut off. Our battery was discharged.

An intrepid ham is never dissuaded by the flings and arrows of time which, when taken at a tide, leads to Field Day. I decided to move the operations to the farm cottage where we had power. But there was no supporting tree nearby. I decided to use the SUV as support.

We packed the SUV at an approximately correct distance from the vernadah of the cottage. We carried the mast over to the SUV and strapped it at two points: on the foot rest and on the overhead luggage rock. At this point the Spiderbeam fiberglass collaspible mast took a commercial break and demonstrated rapid collapse, into the much vaunted 5 feet size. Rayyan was rolling in the grass with mirth. This divided my anger between two opposing directions: toward  my progeny and toward my antenna mast. I didn't move.

I thought like an engineer.  The curious fellow and I carried the mast to an illuminated part of the farm, laid it down, and scotch taped each section to the next as the spiderbeam folks had warned us to do. It is strange how memory works better when your blood pressure is up. 

The mast went up again, this time strapped to the SUV's rack, door column, and the footrest. I setup the radio on a table outside the cottage, running the extension cord from inside. The SUV and the antenna were too far for the EFHW  to reach the radio. 

We asked Humera (XYL) and the girls who were watching us while having their mulberries to DO SOMETHING and not just SIT THERE. So, Humera got inside the SUV and started to roll it towards the cottage. A loud crunching sound announced the sad departure of the sunflower plants we had tied the other end of EFHW from  mother Earth. The EFHW had unrooted its support as the SUV pulled it away. These minor inconviences never deter a determine man, remember Gandhiji! 

Finally everything was in place, and we fixed up the rig but the microphone wouldn't key up. So what? I can just operate from the in-built mic and the thoughfully provided on-screen keyboard for CW, right? Well I could but I needed to key CW contiuously to set the SWR. So I opened up the mic. The curious fellow who had carried the radio to the new operating position was new to radio etiquette. He had just picked up the radio and walked, dragging the mic through the slush and weeds. The mic connector had come out.

I took the matters into my hands, by now, Rayyan was trying to show empathy for the old man by making loud noise like Aww! Shucks! and other unmentionables. I cut the cable with teeth, unbraided a small section and wired it up on the connector so I could short it to key the rig. Why can't the imbecile radio designers think of providing a tune button on the screen??

Finally, everything was in place. I tuned up and AIR net was on. This is the national evening SSB net on 7150. I tried breaking in with SSB a few times but didn't get through. Finally, I changed to CW and called. The net control asked "the CW station to QSY, this is the AIR net....". Finally some other SSB station who could copy my CW translated my CW to the net control and we had a three way contact.

At this point the girls declared we had to head home now that I had had my contact.

I was about to let out my public school vocabulary when I heard them say that they were hungry and there was lamb curry at home. The idea of getting back home and drying out, and eating the hot lamb curry and mangoes was too much for me. We folded up. But the mast refused to collapse. The curious fellow who had taken charge of the mast engineering had finally gotten hang of it. With superhuman strength, he had pulled the section of the mast out so tightly that no power on earth could potentially loosen them. I decided to trick the mast into thinking that we wanted it to stay up, so we put it back up vertically and slammed it into the ground. It dutifully woke up and demonstrated the much vaunted ability to fit back into a 5 feet tube.

I looked into the darkness to find the EFHW winder but I couldn't locate it. The curious fellow had left, scared by the racket the radio was making. The cow and the calf had gone home. We too headed back home. 

In the picture, you can see Rayyan standing while I am checking into AIR net. In the background is the SUV with spiderbeam fiber mast that is easy to carry in a 5 feet size.

73, de Farhan VU2ESE with a little help from my friends and family.

The Wizard of Schenectady -- Charles Proteus Steinmetz

Such a beautiful article.   Ramakrishnan VU2JXN sent it to me.  It reminded me of how puzzeled we were when we found "Schenectady" on old shortwave receiver dials, amidst truly exotic locations.  Rangoon!  Peking!  Cape Town!  Schenectady?   Obviously this was due to General Electric's location in that New York State city.  But reading this article, I am thinking that the presence of Charles Proteus Steinmetz had something to do with it. His informal title (The Wizard of Schenectady)  confirmed that we have been right in awarding similar titles to impressive homebrewers. 

Here is the Smithsonian article that Ramakrishnan sent. 

https://www.smithsonianmag.com/history/charles-proteus-steinmetz-the-wizard-of-schenectady-51912022/#ixzz2lRMjrfit

And here is a link to a PBS video on Steinmetz: 

https://www.pbs.org/video/wmht-specials-divine-discontent-charles-proteus-steinmetz/

Here is a SolderSmoke blog post about "Radio Schenectady":

https://soldersmoke.blogspot.com/2020/07/radio-schenectady.html

Long-time SolderSmoke supporter Ramakrishnan VU2JXN Interviewed on QSO Today

 

https://www.qsotoday.com/podcasts/vu2jxn

I think we got our first e-mail from Ramakrishnan way back in 2006.  At the time he was VU3RDD. On June 22, 2008 in SolderSmoke #86 we reported on the birth of Ramakrishnan's new harmonic.  In this interview with Eric 4Z1UG we hear of Ramakrishnan's daughter (the same harmonic) getting her ham license and working with her dad on electronic projects.  Ramakrishnan has been with us for a long time!  

It was very cool to hear Ramakrishnan talk about the Lamakaan convention, the BITX 40, and the book The Electronics of Radio.  There was a nice mention of SolderSmoke and Pete. 

Listen to the interview here:  https://www.qsotoday.com/podcasts/vu2jxn

Thanks Ramakrishnan!  Thanks Eric! 

Check out the Hyderabad, India Hamfest! LARC-6

This all looks very familiar.  It is very much like the hamfests and rallies I've seen in the US and UK. 

Note in the video above that we see the HF Signals table and our good friend Farhan VU2ESE.

I was privileged to speak to the convention about my Mythbuster transceiver: 

https://soldersmoke.blogspot.com/2023/12/mythbuster-video-for-lamakaan-amateur.html

  

Joseph VU2JQE recorded and uploaded many short videos on the LARC-6 convention and hamfest.  You can see the on his YouTube page:  https://www.youtube.com/@VU2JQE  Thanks Joseph and thanks to the Lamakaan ARC. 

Mythbuster Video for the Lamakaan Amateur Radio Club of Hyderabad, India

I was really pleased when Farhan asked me to speak at this year's Lamakaan Amateur Radio Club convention.  He asked me to talk about my Mythbuster 75 and 20 meter SSB rig.  It was especially nice to talk about this rig because so much of the inspiration and circuitry for it came from Farhan's BITX rigs.  

I recorded a video so that we could avoid WiFi trouble -- the video appears above.  Below you can see photos of the convention and the presentation of the video.  

Thanks Farhan and thanks to the Lamakaan ARC! 

"My Radio My Life" A Film about Radio Enthusiasts

My Radio My Life | Trailer | 4K from Makarand Waikar on Vimeo.

Wow!  VU2DTR is presenting a film about radio made by her mom VU2RBI.  They are showing it in Bethesda, Maryland today.  

Trailer above, summary below:  This looks really great.  I hope we can see the whole film on-line soon! 

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Set in the 21st century, the film revisits the golden era of radio in, when it was the dominant, popular, and only source of entertainment, news, and knowledge.

Being a medium that is heard across national borders, the radio has been instrumental in expanding horizons and enriching the lives of generations. Besides giving companionship to individuals, the radio brought families together and inspired people to make life choices.

Radio continues to enthrall people with its evolving nature and the sentiments associated with it.

Sunburst and Luminary: Apollo "Rope" Memory, and other items of interest

 

Wow.  That is the method that they stored computer memory for the moon missions.  When they were satisfied with a program they would say it was time to "put it on the rope."  

Here's an article on the women who built the rope memory (and the integrated circuits used in Apollo). This reminded me of the women's collective in Hyderabad that "wove" the ferrite core transformers for Farhan's BITX rigs: 

https://www.sciencenews.org/article/core-memory-weavers-navajo-apollo-raytheon-computer-nasa#:~:text=Core%20memory%20used%20metal%20wires,to%20create%20a%20particular%20pattern.

Here is a Wikipedia article on core rope ROM memory with some great illustrations: 

https://en.wikipedia.org/wiki/Core_rope_memory

The Rope

Other stuff of interest that I have spotted so far in the book Sunburst and Luminary -- An Apollo Memoir by Don Eyles:  

-- Not long before the fatal Apollo 1 fire, an MIT colleague of Don Eyles had a drink with Astronaut Gus Grissom.  Grissom unloaded about the poor state of the spacecraft, saying that, "What we have here is a Heathkit."  Grissom died in the fire. 

-- Eyles mentions the use of 6L6 tubes in analog audio amplifiers. 

-- MIT's Doc Draper used a Minox camera.  

-- When the Apollo 11 astronauts came back and were living for two weeks in an isolation chamber, NASA had bulldozers on standby to bury the whole thing ("astronauts, staff and all") in case some dangerous moon bug was detected.  (Is that true?) 

-- At one point soon before an important missile test, engineers realized that they needed an isolation transformer.  They did not have enough time to order one.  So they took an isolation transformer out of one of their soldering stations and used it in the missile.  It worked. Sometimes you just use what you have on hand. 

HB2HB -- A Contact with Denny VU2DGR (video)

At first I didn't realize it was Denny.  On September 11, 2023 at about 2330Z I had walked back into the shack after dinner.  I think DX spots showed an Indian station on 20 meter SSB.  Without realizing who it was, I tuned him in on my Mythbuster rig, heard the other station sign off, and quickly threw in my call.  Denny came back to me right away, and I think both of us then realized that we recognized the call of the other station. Wow, it was Denny, VU2DGR, the Wizard of Kerala!   At the time of the QSO, I didn't have my phone with me; after we spoke, I went to get it,  so the video above captures part of Denny's subsequent contact. (You can also at one point hear Guapo barking.) 

Denny has been running a wonderful station that combines SDR gear with and HDR tube type amplifier and a homebrew Moxon.  

Here is Denny's station. The transceiver is a RadioBerry.  the amplifier and power supply are on the other table.  

Here is the homebrew tube-type amplifier.  This is the part of the station that really puts the HB in HB2HB! That's the power supply on the left and the amplifier itself on the right: 

That amplifier has three 807s in it, with a 6L6GC: 

Here's a video on the RadioBerry transceiver. 

Finally, here is Denny's magnificent homebrew 20 meter Moxon: 

Thanks Denny! 

The Wizard of Kerala (India) -- Denny VU2DGR -- SDR and HDR

 

His signal was just booming in on 20 meter SSB yesterday evening.  It was one of the strongest signals I've heard from India.  I wasn't able to get through the pileup, but I heard mention of a homebrew station at his end...  Sure enough a look at his QRZ.com site shows that a LOT of solder has been melted in his shack.  Both SDR and HDR stuff.  Tube projects including an 807 amplifier made from "components collected from the scrapyard." And a homebrew 20 meter Moxon.  Check it out: 

https://www.qrz.com/db/VU2DGR 

FB Denny!

Kerala is on the southwest tip of India.  It is something of a hotbed of technological innovation.  My only Indian contact using my current series of homebrew dual-banders was with VU3TPW -- Renju is also in Kerala. 

Canadian Build of the Direct Conversion Receiver -- Do This in Your Town! (Video)

This is so cool.  We have been getting reports from Daniel VE5DLD up in Regina, Saskatchewan, Canada.  Daniel is a teacher and he has been building the receiver with a group of students.  

They have been doing very well.  They may end up having more success than we have had here.  

This morning Daniel fired up his build of the receiver and it was inhaling 40 meter signals.  You can hear the CW and the FT8 and you can also hear shortwave broadcast signals just above the 40 meter frequencies.  Congratulations to Daniel!  He is now one of very few radio amateurs who has homebrewed a receiver.  I think his students will soon do the same.  

Daniel's students have built several of the boards and appear to be on the brink of full success.  

Their PTOs look very nice. 

The AF amps were the most challenging of the boards.  Theirs look great.  Excellent soldering. 

We want the receiver project that we carried out at our local high school to serve has a model for others.  After all, we got our inspiration from Farhan in Hyderabad.  We want to see this kind of homebrewing continue.  All of the information on this receiver is on our Hack-A-Day.io page: 

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

We strongly encourage others around the world to find ways to use this project to teach analog electronics.   We think the circuit strikes the right balance between simplicity and usefulness -- when they are done, the students will have a useful receiver capable of worldwide reception.  

Please let us know if you are building this receiver; we are especially interested in the use of this receiver in student-focused group-build projects.  

Jerry KI4IO (Wizard of Warrenton) Describes His ALL ANALOG Phasing Transceiver -- Bob Crane FDIM interview #3 (audio)

Wow, this one really resonated with me.  Jerry had me won over when, early in the interview, he described his decision to dispense with the Si5351/Arduino combo:  "I said the hell with this digital stuff!"  I hear you Jerry.  I feel your pain OM.  

Jerry then goes on to describe a rig with bits of circuitry from some legendary sources:  The Ugly Weekender transmitter.  SSDRA and EMRFD.  W7ZOI's 1968 Direct Conversion receiver.  

Jerry discusses the "presence" of the direct conversion receiver.  And he decries the pernicious effects of AGC.  (Indeed, real hams MANUALLY control the gain.) 

The Wizard of Warrenton then shares some important tribal wisdom:  After building that new piece of gear, leave it on the bench for a couple of weeks.  Beware of "radio infatuation" (what a great term -- we will have to include this in the lexicon).    Jerry points out that while at first, the new rig will seem just perfect, with time time the need for improvements and modifications will become apparent. 

Jerry also has connections to India and Nepal (where he helped Father Moran).  See: https://www.qrz.com/db/KI4IO

Here is W8SX's interview with Jerry: 

http://soldersmoke.com/KI4IO23.mp3

Thanks Jerry!  Thanks Bob! 

Troubleshooting an Intermittent with Mr. Carlson. And Troublesome Tube Re-Branding.

This is a really great video on how Mr. Carlson (VE7ZWZ) did troubleshooting on a tube-type receiver. The problem was an intermittent.  They can drive you nuts, but Mr. Carlson show us how to stay sane. 

-- His use of ordinary observation at the start of the process is very important.  He notices a flickering glow in the voltage regulator tube.  The flickering coincides with the intermittent noise that he is trying to fix.  That is an important clue. 

-- He also can see that the grid of one of the AF amplifier tubes is getting way too hot: grid emission.  That is another important clue.  

-- He checks the grid voltage on the AF amplifier and finds that it is way too low.  It is fine on the other side of the resistor that carries the voltage to the tube.  But it is close to zero at the grid.   This means that the mica capacitors on the grid are suspect. 

-- He uses some fairly esoteric test gear -- a homemade device and an an old Heathkit signal tester -- to check his diagnosis.  They confirm that the mica caps are the problem.  He replaces the caps and the problem is gone.  A very satisfying troubleshoot. 

Mr. Carlson presents us with a lot of good info: 

-- 6K6 tubes were often in fact 6V6 tubes.  And 12AX7s were often 6VJ8s!  Manufacturers were deliberately re-branding tubes. So we shouldn't be surprised if some of our solid state devices turn out to be a bit different from what was promised.  This practice goes way back. 

-- I liked Mr. Carlson's final sensitivity test on the receiver -- he just waved his hand near the antenna connection and we could hear the receiver respond.  Excellent. 

-- Mr. Carlson is very negative about the use of polystyrene caps in oscillator circuits.  But we these simple and cheap caps being used to good effect in oscillators in India.  

-- The leaky and bad micas were a bit surprising.  Carlson speculates that their proximity to heat-producing resistors might have caused the trouble. 

Finally, it is interesting to hear the Canadian pronunciation of radio words:  Solder with the L pronounced (as in the UK).  Farad with the second A long and the final D emphasized (I say it just as the first two syllables of Michael Faraday's last name). 

Thanks Mr. Carlson. 

Pictures from Farhan's Hyderabad High-School Direct Conversion Workshops

 

Farhan came up with the idea of having high school students build their own receivers. We followed his lead -- there are now several such projects underway around the world. 

The simple but effective Colpitts circuit that Farhan recommended. 

The PTO tuning idea came out of  his "Daylight Again" transceiver. 

Oscillation!  

Farhan's High-School Direct Conversion Receiver Workshops in India

Farhan sent this picture yesterday.   If you look closely you can see the students holding their homebrew 40 meter Direct Conversion receivers.  You can even see that they are using the same kind of PTO coil forms that we are using here.  Farhan reports that 11 receivers were built by 33 students.  A few more are being finished and will soon be active in Hyderabad. 

I was really blown away by this picture.   We are doing the same things on different sides of the world.  Our students will like this.  It will be as if they are seeing people of the same age building the same receivers 7,500 miles away.  

In our last session I mentioned to our students that Farhan of Hyderabad had given us the toroidal transformers that they are putting into their mixers.  I told them that in ham radio, when we use parts given to us by a friend we add "soul to the new machine."   And I said that Farhan would be coming to see them in May.  They were really impressed. 

We are starting to see similar efforts in different parts of the world -- Andreas with university students in Germany,   Daniel with high school kids in Canada.   We hope there will be others. 

Progress Report: High-School Students Build Diode Ring Mixers (Board #2 of 4). Hyderabad Soul Added to the New Machines

Dean KK4DAS works with students

A team from the Vienna Wireless Society was back in the local high school Thursday and Friday of this week, helping the students finish their variable frequency oscillators and build their diode ring mixers.  Club President Dean KK4DAS was in the lead, and did an amazing job working with the school and procuring all the needed parts.  Mike KD4MM  and Don KM4UDX provided patient and understanding help to the students. 

Students at work on the receiver

On the oscillators, the students  had to add about six parts to install a buffer circuit built around a J310 FET.  They also had to replace some of the 3D printed coil forms for the main-tuning variable inductor. (Dean KK4DAS made some really nice forms -- see below.)   Several teams of students experiences were very pleased to get their oscillators running. 

Manhattan Mixer Pads

Then it was on to the diode ring mixer.  We had planned on having the students wind their own trifilar toroids, but we realized that this might be too much -- it would add a lot of time to the build, and would introduce a lot opportunity for error.  

One of Farhan's transformers

I remembered that Farhan had given me a big supply of FT-37-43 trifilar toroids that had been assembled in Hyderabad.  We decided to use these transformers.  We reasoned that this was not a big deviation from our DIY ethos -- after all, we didn't ask the student to wind their audio transformers, nor did they wind the RF choke in the VFO buffer.  But we faced a problem:   the Hyderabad transformers were all wound with the same color wire on all three turns.  This would make it hard for the students to figure out which wire went where (there were 12 such wires on each mixer board!).   I figured out how to do this:  The night before, I soldered together the center tap wires, and I twisted together the input coil wires.  We told the students to first solder the center taps in place, then solder the two free wires to the diode ring, and finally untwist the input coil wires, soldering in these connections.  This worked.  

How the transformers were prepped

Before we started, I gave the students a quick class on the essentials of mixers. And I pointed out that we were using transformers made in Hyderabad India and donated by our friend Farhan.  I told the students that whenever we include parts given to us by a ham radio friend we are adding "soul to the new machine." Indeed, Farhan's toroids added a lot of soul. 

We have been insisting that the students have each stage tested before moving on to the next.  This week we used signal generators to put RF and VFO energy into the mixers, and oscilloscopes to make sure that audio was coming out.  

One of the test set-ups for the mixers

The students are making good progress.  After today's session we did an estimate of where each of the projects stand at this point: 

We are building 15 receivers. 
Oscillation without the buffer:   11
Oscillation with the buffer: 5 
Mixer built and tested (but no diplexer yet):  5 
Mixer working, diplexer built  2

During the next month or so the students will build the bandpass filter and the audio amplifier, and put all the boards together to complete the receiver. 

Farhan's Direct Conversion Receiver

Thank God for the Wayback machine.  For a moment I feared that this article about Farhan's DC-40 receiver had been lost.  (Phonestack is now some Vietnamese vendor. ) But the WayBack Machine archive came through for us.  

https://web.archive.org/web/20171109081542/http://www.phonestack.com/farhan/dc40.html

Farhan's receiver has been covered on this blog before, but it is especially relevant for us now that we are immersed in our own direct conversion receiver project.  Farhan was working with his niece, who was a student.  We are working with high school students. 

I really like Farhan's blow-by-blow description of the build.  There are raw emotions here: He speaks of his hatred of LM-386s, and of how he thought of using the copper clad board as a projectile.  His niece wonders about the possibility of evil spirits in the receiver. The battle against AM breakthrough is very familiar.  (I like the RF choke idea.) You won't find candor like this in QST or QEX.  

Farhan's DC-40 project was one of the inspirations for our high school effort.  In fact, when we first went to the school, I left behind a direct conversion receiver that I had built.  Taped onto the bottom of the receiver was a quote from the DC-40 article and a picture of the Wizard of Hyderabad.  (See above, and click on the picture for a better look). 

This week we will inject some more Farhan-ismo into our receiver.  The time has come to build the mixer.  Like Farhan, we will go with the diode ring.   Winding the transformers would be very time consuming.   I remembered that on his visit, Farhan had left me a box of trifilar toroids wound by the seamstresses of Hyderabad using FT37-43 cores.  We will uses these in our build.  They will add a lot of soul to the new machine. 

Did Marconi Cross the Atlantic with a Coherer? No.

Jagadish Chandra Bose

A while back I posted the re-mastered version of the excellent "Secret Live of Machines" episode  on radio.  Among other amazing things, Tim and Rex build a spark radio transmitter and a receiver that uses a coherer and a tapper.  They even set up a demonstration and sent signals from the pier to the shore.  Very cool.  

I shared this with George WB5OYP of the Vienna Wireless Society because he had been looking carefully at the gear that Marconi allegedly used to make that first transatlantic contact.  George wondered if Marconi could have really done this with a coherer as his detector; he was -- for good reason -- skeptical.  Could a glass tube filled with metal filings really detect radio waves sent from across the mighty Atlantic?  

Marconi claimed that he did it with a coherer as the detector: 

On December 12, 1901, Marconi attempted to send the first radio signals across the Atlantic Ocean, in spite of predictions that the radio waves would be lost as the earth curved over that long distance. He set up a specially designed wireless receiver in Newfoundland, Canada, using a coherer (a glass tube filled with iron filings) to conduct radio waves, and balloons to lift the antenna as high as possible. The signals were sent in Morse code from Poldhu, Cornwall, in England. Marconi later wrote about the experience:

"Shortly before midday I placed the single earphone to my ear and started listening. The receiver on the table before me was very crude -- a few coils and condensers and a coherer -- no valves, no amplifiers, not even a crystal. But I was at last on the point of putting the correctness of all my beliefs to test. The answer came at 12: 30 when I heard, faintly but distinctly, pip-pip-pip. I handed the phone to Kemp: "Can you hear anything?" I asked. "Yes," he said. "The letter S." He could hear it. I knew then that all my anticipations had been justified. The electric waves sent out into space from Poldhu had traversed the Atlantic -- the distance, enormous as it seemed then, of 1,700 miles -- unimpeded by the curvature of the earth. The result meant much more to me than the mere successful realization of an experiment. As Sir Oliver Lodge has stated, it was an epoch in history. I now felt for the first time absolutely certain that the day would come when mankind would be able to send messages without wires not only across the Atlantic but between the farthermost ends of the earth."

https://www.pbs.org/wgbh/aso/databank/entries/dt01ma.html

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I mentioned this in SolderSmoke Podcast #242.  This resulted in a very interesting message from Steve AB4I: 

The reason that I am writing is to comment on the coherer and Marconi's transatlantic test. One of my research interests in my doctoral studies was the development and evolution of early radio detectors.  Marconi did not use a coherer for the successful transatlantic tests, but secretly used a detector and telephone receiver that had been invented by the Indian polymath Jagadish Chandra Bose of Calcutta.  Bose's iron-mercury-iron detector was sensitive to a wide range of wavelengths and he used the detector in his 60-GHz millimeter wave and experiments. Bose presented his results to the Royal Society in London in 1899 and his paper was published in the Proceedings of the Royal Society the same year.  Marconi came by the mysterious mercury coherer detector through a friend in the Italian Navy who constructed the device from Bose's paper in the Proceedings in an effort to improve the performance of the Marconi equipment aboard . The Bose detector was superior to anything that Marconi had and was key to the success of the transatlantic tests and for Marconi's subsequent successes. Marconi then filed a patent for the detector in his own name in 1902, even though it was not his invention.  

A lot of nasty business went on in the early days of wireless. The scandal around the "Italian Navy coherer" raged for years, but eventually the role of Bose was revealed. The popular view of Marconi as radio inventor extraordinaire is idealistic, because he did not actually invent anything, but he was very good at dragging laboratory hardware into the real world to serve practical ends.  In every case, crucial parts of Marconi's patents were stolen or copied from other sources and successfully defended through aggressive litigation, deep financial backing, and extensive public relations through advertising and newspaper interviews. Marconi absolutely deserves recognition for his successes in the development of practical wireless communications although he is not noted for his ethics. Marconi's reputation is a bit tarnished nowadays, but that of Jagadish Chandra Bose has blossomed and he is now acknowledged for his epochal work that was fully a half-century before his time.

As for the coherer, we still do not have a full understanding of how the thing actually works.  The cohesion effect of small particles clumping together in the presence of a static charge has been known from antiquity as evidenced by dust bunnies under beds through the ages. There were coherer-like lightning arrestors used on telegraph lines just after the American Civil War and in 1879 David Hughes found that a carbon microphone with loose contacts could detect arcing in nearby equipment and from considerable distances too.  He was told that the phenomenon was nothing new and he just missed the discovery of radio waves.  Thanks to some monumentally bad advice we now speak of Hertzian Waves instead of Hughian Waves.  Branly made a detailed study of resistance changes in metal particles and is generally acknowledged as the inventor of the coherer detector. Oliver Lodge coined the name 'coherer' and demonstrated the detection of Hertzian waves in 1894 a few months after Hertz's death.  Lodge wrote a tribute to Hertz, which was to inspire the young Marconi to begin his own experiments with Hertzian waves.

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Hack-A-Day looked at all this back in 2016:  

https://hackaday.com/2016/01/19/j-c-bose-and-the-invention-of-radio/

Here are the key passages:  One improvement invented by Bose in 1899 was the iron-mercury-iron coherer, with a pool of mercury in a small metal cup. A film of insulating oil covered the mercury, and an iron disc penetrated the oil but did not make contact with the liquid mercury. RF energy would break down the insulating oil and conduct, with the advantage of not needing a decoherer to reset the system.

Bose’s improved coherer design would miraculously appear in Marconi’s transatlantic wireless receiver two years later. The circumstances are somewhat shady – Marconi’s story about how he came up with the design varied over time, and there were reports that Bose’s circuit designs were stolen from a London hotel room while he was presenting his work. In any case, Bose was not interested in commercializing his invention, which Marconi would go on to patent himself.

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Here is a lot more background on Dr. Bose: 

http://www.cse.iitm.ac.in/~murthy/sirjcbose.pdf

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I think the more we learn about Marconi, the less admirable he seems. 

Is Envelope Detection a Fable? Or is it Real? Diodes, Square Laws and all that

HOW ENVELOPE DETECTION (SUPPOSEDLY?) WORKS 

Most of us grew up with the above diagram of how a receiver detects (demodulates) an AM signal. Here is how they say it works: 

--  Because of the way the sidebands and the carrier in the transmitted signal interact, we end up with a signal whose "envelope" matches the frequency of modulation. And we just need one side of the envelope. 

-- We used a simple diode to rectify the incoming signal. 

-- A simple filter gets rid of the RF. 

-- We pass the resulting signal through a capacitor and we get  audio,  which we listen to. 

REASONS FOR SCEPTICISM

But recently, a member of my local radio club has questioned this explanation of AM detection.  He maintained that "envelope detection" is not real, and that was actually happening was "square law" mixing. I guess there are reasons for skepticism about the envelope detection explanation:  The envelope detection explanation does seem very (perhaps overly) simple. This does sound a bit like the kind of "dumbed down" explanation that is sometimes used to explain complex topics (like mixing). Envelope detection does seem consistent with the incorrect insistence from early AMers that "sidebands don't exist." (Of course, they do exist.)  All the other detectors we use are really just mixers.  We mix a local oscillator the incoming signal to produce audio.  Envelope detection (as described in the diagram above) seems oddly different.  

Denial of envelope detection can even be found in the ARRL handbook:  On page 15.9 of the 2002 edition we find this:  "That a diode demodulates an AM signal by allowing its carrier to multiply with its sidebands may jar those long accustomed to seeing diode detection ascribed merely to 'rectification.'  But a diode is certainly non-linear. It passes current only in one direction and its output is (within limits) proportional to the square of its input voltage. These non-linearities allow it to multiply."  

ISN'T THIS REALLY JUST MIXING, WITH THE CARRIER AS THE LO? 

It is, I think, tempting to say -- as the ARRL and my fellow club member do -- that what really happens is that the AM signal's carrier becomes the substitute for the VFO signal in other mixers.   Using the non-linearity of the square law portion of the diode's characteristic curve, the sidebands mix with the carrier and -- voila!  -- get audio. In this view there is no need for the rectification-based explanation provided above. 

But I don't think this "diode as a mixer, not a rectifier" explanation works: 

In all of the mixers we work with, the LO (or VFO or PTO) does one of two things: 

-- In non-switching mixers it moves the amplifier up and down along the non-linear characteristic curve of the device.  This means the operating point of the device is changing as the LO moves through its cycle.   A much weaker RF signal then moves through the device, facing a shifting operating point whose shift is set by the LO.  This produces the complex repeating periodic wave that contains the sum and difference frequencies. 

-- In a switching mixer,  the device that passes the RF is turned on and off.  This is extreme non-linearity.  But here is the key:  The device is being turned on and off AT THE FREQUENCY OF THE LO.  The LO is turning it on and off.  The RF is being chopped up at the rate of the LO. This is what produces the complex repeating wave that contains the sum and difference frequencies.  

Neither of these things happen in the diode we are discussing.  If you try to look at the diode as a non-switching mixer, well, the operating point would be set not by the carrier serving as the LO but by the envelope consisting of the carrier and the sidebands.   And if you try to look at is as a switching mixer you see that the switching is being controlled not by the LO but by the envelope formed by the carrier and the sidebands.  

Also, this "diode as a mixer" explanation would require the diode to be non-linear.  That is the key requirement for mixing.   I suppose you could make a good case for the non-linearity of solid state diodes, but the old vacuum tube diodes were quite linear.  The rectifying diode mixer  model goes back to vacuum tube days.  The "diode as rectifier" model worked then.  With tubes operating on the linear portion of the curve, the diodes were not  -- could not -- have been working as mixers.  We have just substituted solid state diodes for the tubes.   The increased non-linearity of the solid state diodes does introduce more distortion, but the "detection by rectification" explanation remains valid. 

Even in the "square law" region (see diagram below) an AM signal would not really be mixed in the same way as signals are mixed in a product detector.  Even in the square law region, the diode would be responding to the envelope. Indeed, the Amateur Radio Encyclopedia defines "Square Law Detector" as "a form of envelope detector."   And even in the square law region, the incoming signal would be rectified. It would be moving above and below zero, and only one side of this waveform would be making it through the diode.   Indeed the crystal radio experts discuss "rectification in the square law region" (http://www.crystal-radio.eu/endiodes.htm )  So even in the square law region, this diode is a rectifying envelope detector. 

http://www.rfcafe.com/references/electrical/ew-radar-handbook/detectors.htm

THE BEST PROOF

Here is what I think is the best proof that the "envelope detection" explanation is real:  In this video, we see someone build an envelope detector in a simulator.  Watch as he then traces the signals as they move through the diode, the RC filter, and the coupling capacitor.  He goes through it cycle-by-cycle.  You can clearly see how the rectification of the AM leads to envelope detection.

 

The rectifying envelope detection model goes way back in radio history, back to when authors did not shy away from complex technical explanations.  Terman knew how mixers worked, and his 1943 "Radio Engineers Handbook" went to 1019 pages. Terman presented it as a rectification-based detection of the envelope.  I think envelope detection is real, and that Dr. Terman was right. 

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Some links that might help: 

Analog Devices  has a very good, rigorous site showing how envelope detectors work: 

https://wiki.analog.com/university/courses/alm1k/circuits1/alm-cir-envelope-detector

Here is great article by W4ENE on Envelope Detectors and how they have been used in ham receivers over the years: 

http://www.tonnesoftware.com/appnotes/demodulator/EnvelopeDemodulators.pdf

This QEX article begins with some useful vector diagrams showing how the sidebands and carrier combine to form an envelope that is equal to the frequency of mondulation: https://swling.com/blog/wp-content/uploads/2009/08/syncdetectionarrl.pdf

RF Cafe has some good graphs showing the linear and "square law" portions of the crystal diode's curve (see above): http://www.rfcafe.com/references/electrical/ew-radar-handbook/detectors.htm

The crystal radio guys have a good take on square law detection (note, they just see it as rectification, but on a lower, more parabolic portion of the curve): http://www.crystal-radio.eu/endiodes.htm

Here is a good booklet from 1955 on AM Detectors: https://worldradiohistory.com/BOOKSHELF-ARH/Rider-Books/A-M%20Detectors%20-%20Alexander%20Schure.pdf

SolderSmoke's 2006 Interview with Farhan (and pictures from his 2019 visit)

Farhan in N2CQR shack with ET-2 on bench

October 2019

Here is the YouTube version of the SolderSmoke Podcast #34

 https://youtu.be/q-L4IE9f1aA

Farhan with Bob Bruninga WB4APR (SK) 

https://www.qrz.com/db/WB4APR

With Bill and Abe Lincoln

With Einstein

Correcting an Einstein equation

With Elisa

Tuning Bill's BITX 20