Alan Wolke W2AEW's Build of the SolderSmoke Direct Conversion Receiver

We were already very proud to put Alan Wolke W2AEW in our Hall of Fame.  But Alan put icing on the cake this morning by making his own video about his build, along with some pre-CME video of the machine inhaling CW and SSB (see above).  The SSB is DX, from France.  FB Alan, thanks.  

My only comment to Alan was on the frequency readout.  I noted that many builders had resorted to San Jian PLJ frequency counters.  A few others had done what he did and used the frequency readout feature of their Tiny Spectrum Analyzers.  I told him that at first I had gone very low tech.  It was in fact, quite barbaric.   Check it out: 

I think it is kind of low-tech cool.  I am a bit disappointed that none of the builders have done anything similar.  Mark KI5SRY came the closest, but his solution was relatively spophisticated.  Look, it is not to late.  Get out those index cards and calibrate those screws!  Send in pictures or videos.  

SolderSmoke Podcast #260 FDIM, Hollow State Design, Pete's Bench and the Shelf of Shame, Direct Conversion Project News, How Best to Preserve this Blog?, Dean's Bench and the Desk of Despair, Bill's Bench and the Garage of Grief, MAILBAG

SolderSmoke Podcast #260 is available: 

Audio version:  http://soldersmoke.com/soldersmoke260.mp3

Video version: https://www.youtube.com/watch?v=bZzHSjOTbSY

Quote from the Old Miltary Radio Net:  "Being on the leading edge is great, but sometimes being on the trailing edge is more fun."  Indeed. 

Heard from an Australian on the Southern Cross Net:  "My antenna needs a lot of Viagra!" 

News from Dayton/Xenia/FDIM: Dayton Xenia.   Again, we didn't go.  But Bob Crane W8SX was there and got a nice interview with Grayson,  Hans, and Farhan.  We are presenting these and more.  Michigan Mighty Mite Revival at FDIM!  Jeff W9TH. 

Farhan's review of Hollow State Design: I am compelled to set aside the future of my family and to orphan my cats to resume work on the 250v power supply that I built last year. Inshallah, Allah favors those who favor thermatrons!   Grayson's book is  imbued with deep experimental insights and littered with gems. You have to read it over and over to find new things each time.   It goes into my reference shelf in the lab."  Buy it here: https://www.ermag.com/product-category/books/ 

----------------------------

PETE'S BENCH:

Pete working on JF3HZB dial.  Send Pete a Heath mono-bander! 

MHST on shelf of shame? Even the great ones have to take a break every so often. On the importance of taking a break. Ernest Rutherford 1917 and all that:  https://soldersmoke.blogspot.com/2025/05/on-importance-of-taking-break.html 

Channelized 40 meter rig. Heard in Arizona by Andy KB7ZUT on a HOMEBREW SSB Reciever.  Very rare.   SWL HB2HB. 

Pete:  Thumb broken as a Novice?  Early episode of Fat Finger Syndrome? 

---------------------------

DC RX NEWS:  

Quote from N6QW:  "The radios do not build themselves!"  

Alan W2AEW finishes Direct Conversion Receiver. And even he worries about feedback! 

Phil W1PJE MIT receiver  (with cool MIT stuff).  Coming to see us! 

KN6FVK's Barkausen-Be-Gone Spray :https://soldersmoke.blogspot.com/2025/05/john-kn6fvks-fb-homebrew-soldersmoke.html

Indian hams working DC RX. VU2JXN Ramakrishnan, VU2TUM  Puneit Singh, Ashish N5ASD, building one in Bangalore with 3D printed form from Scott, KQ4AOP.  Ramakrishnan is planning on building a second receiver with his daughter. On June 22, 2008 in SolderSmoke #86 we reported on the birth of Ramakrishnan's daughter.  This is that same daughter! See: https://soldersmoke.blogspot.com/2024/01/long-time-soldersmoke-supporter.html    How to get a PTO form in India.  A tip from Ramakrishnan: "I got the 3d printing done via https://robu.in with 1:1 size. After uploading the stl, I received it by post in 5 days or so."

German students of Andreas DL1AJG.  and Canadian students of Daniel VE5DLD. 

Receiver built in Singapore!  9V1/KM7ABZ

John M0XJA reports 8 members of his club are building this receiver. 

Chuck N4AVC got his PTO coil form 3D printed at the local library. For free!  FB! 

Few admit to being fooled by April Fool story.  But still, inspirational. VK3HN was going for a few seconds -- SOTA AI chatbots? John West liked the 85th harmonic threat. 

What next after DC RX?  Choose carefully! Don't bite off more than you can chew. 

Do some mods!  Build something else!  And remember to be a homebrew Elmer.  Help someone else build the receiver. 

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SHAMELESS COMMERCE DIVISION: 

Check out the SolderSmoke blog on the WayBack Machine.  The blog, not the podcast.  www.soldersmoke.blogspot.com   Would this be a useful backup if Google were to pull the plug on blogspot?  Is the format OK?   Is the template recoverable?  How best should  we backup the SolderSmoke blog?  

Be a Patreon SolderSmoke Sponsor!   Please subscribe to the YouTube channel!  Buy your Amazon stuff through our link.  Buy stuff from Mostly DIY RF.  

-------------------------------

DEAN'S BENCH:

Dean has completed his Mythbuster: https://kk4das.blogspot.com/2025/05/kk4das-mb-20-transceiver-complete.html   Plexiglass top! 

Diode switching. 

Dean:  Build of the SDR receiver.  Microscope required? 

____________________

BILL'S BENCH:

VK6JDW and HCJB in the Kimberly. 

The stages of separation:  Shack, Garage, Car trunk:  HP-8640B and HAMEG scope saved from garage. HP-8640B repair.  HAMEG Modulation Monitor. 

=================

MAILBAG

-- Wouter ZS1KE.  Thinks Soviet spies COULD homebrew.  Hamilton KD0FNR concurs. Agent Sonya and Soviet Spy homebrew. Copacetic Flow. I dunno....I dunno... 

-- Hamilton KD0FNR grew up in New Mexico, supports my idea of Starlink deorbit. See : https://www.kallmorris.com/columns/goodness-gracious-green-balls-of-fire

-- Adam N0ZIB Heard my 10 meter beacon from the DR.  28,233.5 MHz  On now. 

-- Rick N3FJZ  Great memory Direct Conversion messages. 

-- John KN6FVK had fun with DC RX. Tattoos on Board. We need a high sign! Like the Little Rascals. 

-- Adrian M7EFO DC RX builder in GQRP.  FB.

-- Steve KW4H Kits not the same as homebrew, but old Boatanchor kits have value. 

-- Mike WU2D -- Old buddy Charles Kitchen SK. 

-- Craig -- Some really nice feedback on Hack-A-Day re DC RX and Dean's videos. 

-- Peter VK3TPM proposes a certificate for SolderSmoke DC RX Honor Roll. 

-- Michael WN2A used a 3 inch reflector from Northern New Jersey. Edmunds Scientific "Space Conqueror"  

-- Phil W1PJE and Mike WN2A lament that our eyes don't pick up radio frequencies.  This would be a great troubleshooting tool! I can SEE the IMD!  Perhaps some tin foil hats? 

-- John WPE9IRS SW listener! Heard my beacon.  Many SWLs switching to tuning in ham stations. 

-- Peter VK3YE found a homebrew 160 meter double-sideband transciever at a hamfest.  He also found "Solid State Basics for the Radio Amateur -- A QST Anthology"  NOT SSDRA.  But good!

-- Peter VK2EMU  From the Southern Cross (I took a picture of it in the DR!)  Building the DC RX!

 

Ramakrishnan VU2JXN

HCJB is now in Western Australia. In "The Kimberly." And VK6JMS can use their antenna.

I grew up listening to HCJB's shortwave broadcasts from Quito, Ecuador.  Fast forward to the present:  This week I have had two radio contacts with Nic VK6JMS.   His callsign indicates Western Australia.  I assumed he was in the Perth area, but no, he is in the northern part of Western Australia, in the area known as The Kimberly.  Look on the map for the place called Kununurra.  That is where he is.  

Here is Nic VK6JMS's QRZ page: https://www.qrz.com/db/VK6JMS  He has access to some really fantastic antennas.  In his page he refers to them at TCI antennas.  I looked them up: 

 A TCI dipole array refers to a specific type of antenna system designed and manufactured by SPX Communication Technologies, a company formerly known as TCI. These arrays are typically used for high-frequency (HF) radio broadcasting and communications, and they are known for their ability to achieve wide bandwidths and efficient radiation patterns. 

https://www.antenna.be/tci-611.pdf

https://www.antenna.be/tci-613.pdf

---------------------------------------

These antennas are used for the SW broadcasts: 

Since 2003, Reach Beyond (formerly HCJB) has been transmitting from our Broadcast Facility in the Kimberley, in far north Western Australia, to the Asia Pacific region through shortwave radio, and currently broadcasts programs in 25 languages.

Founded in 1931 as radio station HCJB in Quito, Ecuador, Reach Beyond is now a global, partnership-driven ministry. Many people know us as the shortwave ministry that originated in Ecuador which went on to establish hospitals and medical clinics in Quito and Shell. Today the visionary “madness” of our founder Clarence Jones and his band of missionary pioneers lives on around the world. 

Here in Australia, Reach Beyond carries on that vision through its radio broadcast ministry. Our shortwave facility is uniquely placed in Australia to deliver powerful messages of hope to remote and isolated communities throughout the Asia Pacific region.  https://www.reachbeyond.org.au/on-air/

-----------------------------

One thing I noticed about Nic VK6JMS's signal:  there seemed to be a latency delay between when I turned the conversation over to him, and when he began to transmit.  I wonder if the Icom RS-BA1 remote station software that he is using might explain this latency. Any ideas on this?

Stephen VK2BLQ's Very FB EARLY build of the SolderSmoke Direct Conversion Receiver

 

This was back in the old days, long before we had Discord.  It was early 2023, and we were getting ready to start the Direct Conversion receiver project at the local high school.  I put out a version of the SolderSmoke Challenge:  I asked people to build our receiver and let us know if it worked for them.  Stephen VK2BLQ took us up on this and built the beautiful receiver you see above.  

Thanks Stephen.  Welcome to the Hall of Fame!  

Stephen wrote:  

Bill,

Don't worry, you are not alone out there.

Here is my build; sorry that the front panel is overexposed and hard to see, but it is plywood.

I did follow the schematic but due to the contents  of the junk box there have been some component changes.

The only thing that I had to buy was the 3/16 x 50 mm (2 inch) brass screw.

My calculations for the coils for the PTO and  BPF  were  a little  bit off necessitating padding down the PTO with a further 100 pF (easier than remaking the coil and mounting)  and removing a few turns from the T50-6 toroids.

Like other people have found: the audio takes off at full volume; I am thinking but not yet tried adding decoupling between R5 (15K) and C2(47 uF). It isn't the actual values of the electros as I had to use 100 uF so might be the audio output getting back into the earlier stage.

The tuning range I get is  our 7000 to 7200 KHz and some shortwave stations above and below, Turning the screw is a little bit fiddly, but once tuned the vfo is quite stable and the audio sounds good.

Best wishes,

Stephen

VK2BLQ

Peter Parker VK3YE finds a Homebrew Double Sideband Transceiver at an Australian Hamfest

Peter's detective work on the mystery box starts at around 13 minutes into this video.  He quickly found a balanced modulator and did not find a crystal filter.  This led him to correctly suspect a double sideband transceiver.  A look at the LP filter and the VFO led him to suspect a 160 meter rig.  Nice work Peter.  That's what it is:  a 160 meter DSB transceiver. 

I had a similar experience with a direct conversion receiver, but never with a full double sideband transciever.  Nice find.  Peter should try to bring that rig back to life, and he should try to find out who built it. 

The Solid State Basics book by DeMaw and Rusgrove looks good.  I hadn't seen that one, but I will get one. 

Thanks Peter! 

Chris VK1CHW's FB SolderSmoke Direct Conversion Receiver -- With A Very Innovative Homebrew PTO Coil Form

Chris VK1CHW sent us the above "proof of life" video.  And alive it is!  FB Chris.  I especially liked the approach he took to the coil form for the PTO:  He is getting a 3D printed one, but in the meantime he improvised with some electrical conduit and a bolt.  Improvise satisfies!  FB Chris.  Congratulations and welcome to the Hall of Fame.  

---------------------------------

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

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

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke    

Rob VK5RC's FB SolderSmoke Direct Conversion Receiver. MDS?

Rob VK5RC has completed his SolderSmoke direct conversion receiver.  Congratulations Rob.  And it is good to know what we have a Medical Doctor among our builders -- this adds prestige and expertise to the project. 

Rob measures a Minimum Discernible Signal at -95 dbm.  I think that is kind of weak performance.  Much depends, of course, on how you define "descernible."  Some books say you need a 10 db increase in audio.  Others say you just need to be able to tell there is a signal there.  I have gone with the latter definition and have measured MDS of around -120 dbm.   I wonder why there is such a difference in measured MDS.  

In any case, it is great to see Rob's receiver inhaling all of that great Australian SSB (see video above).  Thanks Rob, and congratulations.  

Garry's FB Australian SolderSmoke Direct Conversion Receiver with "Free Tree Printed" PTO Coil Form

Garry built a really nice receiver.  I think he is in Australia.  His PTO coil form is  "a piece off an old rotten Australian red cedar door."  FB Garry. 

Garry did a really nice blog entry on his build experience: 

https://garrysblog.com/2025/03/14/my-build-of-the-soldersmoke-40m-direct-conversion-receiver/

As with Chris, if there was any justice in the world,  Garry would be issued a ham license based solely on this receiver build.  He has done something that 95% of hams have never done: he built a receiver!  

Congratulations Garry! 

------------------------------------------

For more information on how you too can build the receiver: 

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

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

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke

 

VK4PG's Wonderful Australian Direct Conversion Receiver from Sunny Queensland

It was really great to hear those Australian voices coming from Phil's receiver.  Check out the video above. 

Phil writes:  

Completion!  So pleased, it works really well.  And there were lots of lessons for me along the the way.  Thank you Dean, Bill and Pete, it's been a great way to get me into homebrewing.  73s from sunny Queensland.  Phil VK4PG

I also like Phil's front panel.  Note how he put to use the circular piece that remained after cutting the speaker hole; that became the tuning knob.  FB Phil.  Thanks. 

For more information on how you too can build the receiver: 

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

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

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke 

Peter VK3TPM's SolderSmoke Direct Conversion Receiver (and his follow-on DSB transmitter) -- From Australia

Peter VK3TPM is a long-time member of the SolderSmoke community.  He is a software developer and technology commentator based in Melbourne.  But that digital background did not stop him from diving headfirst into this highly analog project.  He fought a lot to get the stages of his receiver working properly.  The AF amp was full of challenges.  He overcame all of them and ended up with a very fine looking and sounding receiver.  See above. 

Going the extra mile, Peter took his newfound abilities into the world of phone transmitters.  He whipped up a 75 meter DSB transmitter and used it to check into two Australian Technical nets: 

 

This is really great.  You can see the look of pleasure and pride in Peter's face as he uses his machine to send his voice far across Australia and into Tasmania.  This is the kind of satisfaction that comes from homebrew.  

I am encouraging him to combine the his DC receiver with additional stages (perhaps from the DSB transmitter) to make a DC-DSB transciever.  

Thanks Peter! 

---------------------------------------------

For more information on how you too can build the receiver: 

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

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

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke 

A Saw the Southern Cross (Crux) This Morning (first time in 30 years!)

You can see it (above) in the picture I took this morning, with my Iphone. 

I think I last saw this important constellation more than 30 years ago.  From my observation log: 

DECEMBER 9 1994. MORNING. Went to Parque Mirador Sur near Hotel El Embajador at 5 a.m. Confirmed that I have been looking at the Southern Cross. Below Corvus, Head of the Cross is on a line from Alpha and Beta Centauri. Base of Cross is "three thumbs" from horizon. I calibrate my thumb with Mars and Regulus at 2 degrees. That puts base of cross at 6 degrees off horizon. My Horizon is (90 -18.5 = 71.5 South. So 71.5 - 65.5 BINGO! Agrees with star map declination for Southern Cross. Also Right arm of cross is faint as indicated on star map. Alpha and Beta Centauri off tothe left. Alpha looks red. Beta seems to have two other stars around it. Eureka: Following the line from Alpha and Beta Centauri to the head of the cross, I found a very distinct circular cluster. I think this is the Jewell Box - NGC 4755 (open cluster). Still trying to figure out the constellation (Argo?) that lies to the right of the cross. Looks to me like the false cross. It is bigger than the Southern Cross. Mine seems to have a cluster off the right arm and the left arm has a dimmer star near it. A good morning! (LATER FOUND THAT MY CLUSTER WAS GLOBULAR CLUSTER RNGC 5139. I HAD MISIDENTIFIED ALPHA AND BETA CENTAURI.) 

Here is what Heavens Above predicted for this morning from Punta Cana: 

 

 

How to Organize a Small Shack

A YouTube comment from Paul VK3HN sent me back to "The Spirited Man" YouTube channel, and one of the first things I found was this video about how to organize a small space.  This is very relevant to my shacks in Virginia and in the Dominican Republic. 

Lots of good ideas here, but that propane heater kind of scared me.  And it seemed inconsistent with concerns behind the fire-preventing garbage can.  What do you folks think? 

Thanks Paul. 

 

Deep Space Station 43 -- Canberra, Australia

 

https://spectrum.ieee.org/apollo-era-antenna-voyager-2

From the IEEE article: 

The dish’s manufacturer took great pains to ensure that its surface had no bumps or rough spots. The smoother the dish surface, the better it is at focusing incident waves onto the signal detector so there’s a higher signal-to-noise ratio.

DSS-43 boasts a pointing accuracy of 0.005 degrees (18 arc seconds)—which is important for ensuring that it is pointed directly at the receiver on a distant spacecraft. Voyager 2 broadcasts using a 23-watt radio. But by the time the signals traverse the multibillion-kilometer distance from the heliopause to Earth, their power has faded to a level 20 billion times weaker than what is needed to run a digital watch. Capturing every bit of the incident signals is crucial to gathering useful information from the transmissions.

The antenna has a transmitter capable of 400 kilowatts, with a beam width of 0.0038 degrees. Without the 1987 upgrade, signals sent from DSS-43 to a spacecraft venturing outside the solar system likely never would reach their target.

https://spectrum.ieee.org/apollo-era-antenna-voyager-2

Paul VK3HN's Video on Scratch-Building and SOTA

It was great to get a comment from Paul VK3HN -- this led to a re-establishment of contact.  Apparently Google knows who I have been e-mailing, so this great video appeared on my YouTube screen.  Thanks Google! 

-- Great to hear Paul's shout out to Pete Juliano N6QW, and Pete's concept of noodling. 

-- Paul's emphasis on testing each stage independently is really important. 

-- Wow, ferric chloride!  It is great to see someone doing this (instead of just sending Gerber files to China). 

-- Books.  This reminds me that I have to get Drew Diamond's books. 

-- Paul's comment on the usefulness of a general coverage receiver.  Right on target Paul.  

-- On the test gear, we can now add the TinySA Ultra.  And you don't have to win the Lotto! 

-- Finally, Paul is absolutely right on the need to constantly update and publish changes to schematics. I am guilty of not doing this. (I hang my head in shame.)   This became a problem in our simple High-School receiver project -- I would make changes to circuits and fail to communicate these changes to Dean KK4DAS.  Paul's method would have solved this problem.  

-- Thanks Paul! 

A Low-Power (QRP) Contact from Australia to Spain (with video from both sides!)

A recent comment on the blog put me back in contact with an old friend of SolderSmoke:  Paul VK3HN.  Paul is an amazing homebrewer -- it was great to hear from him.   He sent along this video of a portable Summit on the Air activation from the Melbourne Australia area.   Paul managed to contact Ignacio EA2BD in Spain.  Ignacio was also running low power with a portable set up.  The remarkable thing is that we have video from both sides of the contact.  FB!  Thanks to Paul and Ignacio. 

A Look at Old Radios in Australia (video)

I thought you guys would like Peter Parker's latest video.  And in it, Dean KK4DAS might see a clue or two for his Halli restoration/repair project.  

What really struck me was the dial markings on the Australian radios.  They seem to be mostly oriented toward the reception of Australian AM or LW broadcasters -- not many exotic DX locations are marked.  Australia is big! 

Looks like a lot of crystal detectors in glass tubes.  At first I thought they might have been coherers, but I think they are crystal detectors. 

Many variometers visible. 

I saw one Geloso-Milano Communications 8 receiver.  Va bene! 

I also saw one "Tasma 780" Superhet.  Cool name! 

What is up with the "Green Theme"? 

I have some of the headphones they showed. 

Please note in the Comments section anything special that you noted in watching Peter's FB video. 

More on the coil winding machine here: 

https://hackaday.com/2023/08/30/all-mechanical-coil-winder-is-a-scrap-bin-delight/#more-612604

Ciprian YO6DXE Puts the Michigan Mighty Mite on AM! (video)

Excellent work Ciprian!  

Here we have a Michigan Mighty Mite being modified for AM in Romania, with input from Hungary, and inspiration from Melbourne, Australia (Peter Parker VK3YE).  With a very nice shout-out to SolderSmoke.  

I really like Ciprian's emphasis on having fun with the electronics. 

TRGHS! 

Australia and Apollo 11 -- Honeysuckle Creek

Trevor reminded me that Parkes ("The Dish") was not the only Australian antenna at work during Apollo 11.  This very nice video gives a more complete description of what happened.  

I saw one piece of Collins gear.  And some of Curious Marc's HP frequency counters.  

More on the Honeysuckle Creek Tracking Station here: https://honeysucklecreek.net/

VK2BLQ Builds the High-School Direct Conversion Receiver

It is truly a thing of beauty.  Stephen VK2BLQ built it just as we designed it, so his build (like those of several others) serves as confirmation that this design is ready for the high school students. 

Stephen writes: 

Bill,

Don't worry, you are not alone out there.

Here is my build; sorry that the front panel is overexposed and hard to see, but it is plywood.

I did follow the schematic but due to the contents  of the junk box there have been some component changes.

The only thing that I had to buy was the 3/16 x 50 mm (2 inch) brass screw.

My calculations for the coils for the PTO and  BPF  were  a little  bit off necessitating padding down the PTO with a further 100 pF (easier than remaking the coil and mounting)  and removing a few turns from the T50-6 toroids.

Like other people have found: the audio takes off at full volume; I am thinking but not yet tried adding decoupling between R5 (15K) and C2(47 uF). It isn't the actual values of the electros as I had to use 100 uF so might be the audio output getting back into the earlier stage.

The tuning range I get is  our 7000 to 7200 KHz and some shortwave stations above and below, Turning the screw is a little bit fiddly, but once tuned the vfo is quite stable and the audio sounds good.

Best wishes,

Stephen

VK2BLQ

I really like the ruler near the tuning control.  Is that (I hope!) the frequency readout? 

But why? Why Can't I Listen to DSB (or AM) on my Direct Conversion Receiver?

I've said this before:  I just seems so unfair.  We just should be able to listen to DSB signals with our beautifully simple homebrew Direct Conversion receivers. I mean, building a DSB transmitter is a natural follow-on to DC receiver construction.  And we are using AM shortwave broadcast stations (Radio Marti --I'm looking at you)  to test our DC receivers for AM breakthrough.  But when we tune these stations in, they sound, well, awful.  So unfair!  Why?   Unfortunately it has to do with laws.  Laws of physics and mathematics.  Blame Fourier, not me.  

Over the years there has been a lot of handwaving about this problem.  From Doug DeMaw, for example: 

In his "W1FB's Design Notebook," Doug wrote (p 171):  "It is important to be aware that two DSSC (DSB) transmitters and two DC receivers in a single communication channel are unsatisfactory.  Either one is suitable, however, when used with a station that is equipped for SSB transmissions or reception. The lack of compatibility between two DSSC (DSB) transmitters and two DC receivers results from the transmitter producing both USB and LSB energy while the DC receiver responds to or copies both sidebands at the same time."

That's correct, but for me, that explanation didn't really explain the situation.  I mean we listen to AM signals all the time.  They produce two sidebands, and our receivers respond to both sidebands, and the results are entirely satisfactory, right?  Why can't we do this with our Direct Conversion receivers?  I struggled with this question before: https://soldersmoke.blogspot.com/2015/07/peter-parker-reviews-dsb-kit-and.html  You can see in that post that I was not quite sure I had the answer completely correct. 

It took some discussion with a fellow Vienna Wireless Society member, and some Googling and Noodling for me to figure it out.  But I think I've got it: 

Imagine a station transmitting a DSB signal at 7100 kHz with a 1 kHz tone at the AF input.  There will be signals at 7101 kHz and at 7099 kHz.  Assume the carrier is completely suppressed. 

We come along with our DC RX and try to tune in the signal. 

Remember that they heart of the DC RX is a product detector, a mixer with the VFO (or PTO) running as close as we can get it to the suppressed carrier frequency (which we can't hear).  

Lets assume that we can somehow get our VFO or PTO exactly on 7100 kHz.  The incoming signals will mix with the VFO/PTO signal.  We are looking for audio, so we will focus on the difference results and ignore the sum results of the mixing.  

The difference between 7101 and 7000 is 1 kHz.  Great! And the difference between 7099 and 7000 is 1 kHz also.  Great again, right?  We are getting the desired 1 kHz signal out of our product detector, right?  So what's the problem?  

Here it is: SIDEBAND INVERSION.  Factoring in this part of the problem helps us see the cause of the distortion that plagues DSB-DC communication more clearly. 

Remember the Hallas Rule:   Whenever you subtract the modulated signal FROM the unmodulated signal, the sidebands invert.  So, in this case, we are subtracting that 7099 "lower sideband" signal FROM the 7100 VFO/PTO signal.  So it will invert.  It will become an upper sideband signal at 1 kHz.  We will have two identical 1 kHz signals at the output.  Perfect right?   Not so fast. Not so PERFECT really.  

The perfect outcome described above assumes that our VFO/PTO signal is EXACTLY on 7100 kHz.  And exactly in phase with the suppressed carrier of the transmitter.  But if it is even SLIGHTLY off, you will end up with two different output frequencies, signals that will move in and out of alignment, causing a wobbling kind of rapid fade-in, fade-out distortion.  You can HEAR this happening in this video by Peter Parker VK3YE, starting at 6:28:

And you can see it in this LTSpice simulation.  

This LTSpice model just shows two diode ring mixers.  The transmitter is on the top, the receiver is on the bottom. The transmitter has RF at 7100 kHz at L1 and audio at 1 kHz at R1.   The receiver has the VFO at 7100.001 L7,  DSB from the transmitter at L12 with audio appearing at R4.  It is instructive to watch the output as you move the VFO frequency.  If you move the VFO freq away from the transmit carrier osc frequency you will see the distortion.  Here is the netlist for the LTSpice simulation: 

http://soldersmoke.com/DSBDC.net

On paper, using simple mixer arithmetic, you can tell that it will be there. With the VFO/PTO just 1 Hz (that's ONE cycle per second) off, you will end up with outputs at 1.001 kHz and at .999 kHz.  Yuck.  That won't sound good. These two different frequencies will be moving in and out of alignment -- you will hear them kind of thumping against each other.    And that is with a mere deviation of 1 Hz in the VFO/PTO frequency!  We are scornful when the SDR guys claim to be able to detect us being "40 Hz off."  And before you start wondering if it would be possible to get EXACTLY on frequency and in phase, take a look at the frequency readout on my PTO.  

Now consider what would happen if the incoming signal were SSB, lets say just a tone at 7101 kHz.  We'd put our VFO at around 7100 kHz and we'd hear the signal just fine.  If we were off a bit we'd hear it a bit higher or lower in tone but there would be no second audio frequency coming in to cause distortion.  You can hear this in the VK3YE video:  When Peter switches to SINGLE Sideband receiver, the DSB signals sound fine. Because he is receiving only one of the sidebands. 

The same thing happens when we try to tune in an AM station using a Direct Conversion receiver:  Radio Marti sounds awful on my DC RX, but SSB stations sound great. 

My Drake 2-B allows another opportunity to explore the problem.  I can set the bandwidth at 3.6 kHz on the 2-B, and set the passband so that I will be getting BOTH the upper and the lower sidebands of an AM signal. With the Product Detector and the BFO on,  even with the carrier at zero beat  AM sounds terrible.  It sounds distorted.  But -- with the Product Detector and BFO still on --  if I set the 2-B's  passband to only allow ONE of the sidebands through,  I can zero beat the carrier by ear, and the audio sounds fine. 

There are solutions to this problem:  If you REALLY want to listen to DSB with a DC receiver, build yourself a synchronous detector that gets the your receivers VFO EXACTLY on frequency and in phase with the transmitter's oscillator.  But the synchronizing circuitry will be far more complex than the rest of the DC receiver. 

For AM, you could just use a different kind of detector.  That will be the subject of an upcoming blog post. 

Please let me know if you think I've gotten any of this wrong.  I'm not an expert -- I'm just a ham trying to understand the circuitry.