A Flight from Chile to Panama: Aeronautical Mobile Contact with KX4WC/AM, with VK3MO in the Group

WA3O sent me an e-mail alerting me to the fact that Mike KX4WC/Aeronautical Mobile would be flying up from Santiago, Chile to Panama City this morning. So I fired up the 20 meter rig and hoped for the best.

Not only was I able to talk to Mike, I was also able to work WA3O, VY2WW, and VK3MO in Melbourne. It was a very FB morning. VK3MO was really booming in. I have worked Ian before -- his 5 over 5 over 5 over 5 array on 20 meters really helps. https://www.qrz.com/db/VK3MO

I was not hearing Mike KX4WC very well until the sun came up over our north-south path. You can see this in the picture below. Thanks to all for this very cool contact.

Ian VK3MO's 20 meter array

Peter VK3TPM had done a very nice profile of Ian and his station: 

https://www.mrarc.org.au/member-profile-ian-vk3mo/

Do I really NEED Tropo to hear the Puerto Rican FM Broadcast Station? Or are we just close enough to do this line-of-site?

 

WIDI 99.5 FM from western Puerto Rico continues to put a full quieting signal into the eastern Dominican Republic.   The station is so regularly strong that this made me wonder if I am really using tropospheric ducting to hear it.  If I was using tropo ducting, I think there should be some variation in signal strength over the course of 24 hours right?  But it is always strong.  Why?  

I checked the distance:  97 miles.   With its antenna at 2800 feet, its visual horizon will be 64.8 miles away.  I am about 98 feet above the ocean.  This means my horizon is 12.22 miles away.  There appears to be a gap, right?  I mean 64.8 + 12.22 = 77.02 miles.   So it looks like there is a gap of about 20 miles.  

But wait!  Mike WN2A reminded me that there is a difference between radio line of sight and visual line of sight.   Radio line of sight = 4/3 of visual line of sight. 

AI explains where the 4/3 factor comes from: 

The radio horizon appears longer than the visual horizon by a factor of about 4/3 due to atmospheric refraction, which bends radio waves slightly downward. To simplify calculations, this effect is modeled by treating radio waves as if they travel in a straight line over a larger, "effective" Earth with a radius 4/3 times the actual radius. This increased effective radius allows radio waves to "see" further over the Earth's curvature, extending the line-of-sight range compared to what is seen by the human eye, which is not affected by atmospheric bending to the same degree. 

So that puts WIDI's radio horizon at 86.4 miles.  My radio horizon is 16.16 miles.   86.4 + 16.16 =  102.56 miles No gap.  We should be able to hear WIDI, even without tropospheric ducting.   

Philippe F1GMA's Fantastic SolderSmoke Direct Conversion Receiver

SSB

Wow, congratulations to Philippe F1GMA for his wonderful build of the SolderSmoke Direct Conversion Receiver. Phillipe deserves extra credit for achieving this goal while working in a foreign language, and with parts acquisition even more of a challenge for him.  That AF transformer was hard to get in France.  And I see that a companion CW transmitter may be in the works.  FB.

The SSB signal that Philippe provides includes a clip from special event station TM120ESP.  That station commemorates the 120th anniversary of the first Esperanto congress.  FB.  TRGHS! 

Congratulations Philippe and welcome to the Hall of Fame.  I think you are our very first French builder.  

Click here for a CW clip

Puerto Rico -- Dominican Republic Tropo on 99.5 FM? Yes, probably

 

Our friend Todd K7TFC in Portland found this in the 1950 ARRL Handbook at an, uh, opportune moment.  TRGHS.  This seems to describe what a I am hearing, especially that "airmass boundary" in the lower left of the diagram above.  

I'm not a VHF guy, and I am a bit surprised at the persistence of this propagation path.  It is 4:30 am here and the adult contemporary rock from Puerto Rico (Kokomo by the Beach Boys!) is full quieting here in the Dominican Republic.  And it is of the same strength during daylight hours. I don't remember this from the winter months, but I may have just missed it. 

Here is what AI (Gemini) says about this: 

https://share.google/aimode/M1HvC7Y893eE5gAcn\

One other factor to consider:   The island of Mona is about halfway across the path.  There are few people there, and there is almost certainly not a repeater of any kind.  But there may be a metal tower or two... 

Gianfranco IU1DZZ and Mike WN2A  both support the tropo hypothesis.  Mike mentions the Hepburn Index.  I will have to read up on that.  Hamilton is also looking at this propagation path.  Thanks guys.  

Puerto Rico FM Broadcast Station Heard in the Dominican Republic -- But How? WIDI 99.5 FM

WIDI 99.5 FM. Booming in during daylight here on the eastern tip of the Dominican Republic. Their antenna is about 2100 feet above average surrounding terrain. That would put the horizon at about 56 miles. But the path is about 100 miles. What do you folks think is the likely propagation mode?

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

Chris KN4GAH's 100th! SolderSmoke Direct Conversion Receiver

This was the 100th SolderSmoke receiver!     It was really cool to see Chris KN4GAH's  receiver inhaling CW (sbove)  and SSB (below).  I especially like the ink pen markings on the pine board.  FB.  Maybe make note of memorable QSOs heard, or -- later -- contacts made with this receiver.  

Chris is an electrical engineer, so it was particularly useful for us to get his perspective on this project.  We started this at the High School knowing full well that most of the students would spend their careers in the high tech, digital world, and might never again touch a soldering iron.  But we thought it would be good for them to build something like this at least once.  Chris comments on this idea below.  

Chris writes: 

Thank you for putting this all together for all of us and creating such a great community full of knowledgeable and helpful people. I work as an RF engineer and mentor a few junior RF engineers and will be proposing this challenge to them as a learning opportunity. As this challenge provides a lot of insight into how common blocks used in RF designs operate. It is just too easy to go on mini-circuits and find a filter, amp or mixer that meets ones needs. Actually building these components provides valuable knowledge that all us RF engineers should have.

Thanks Chris, Congratulations and welcome to the Hall of Fame!

Chris KD4PBJ's FB SolderSmoke Direct Conversion Receiver

Chris KD4PBJ is one of SolderSmoke's most loyal fans.  Over the years Chris has supplied many of the parts and ideas used in SolderSmoke projects.  We were really delighted when Chris took on the Direct Conversion challenge.  As you can see,  his build was superb. 

Chris had promissed to have the receiver completed by September 2, 2025.  As it happens, that was the day of some very powerful solar activity and very poor band conditions.  So the video above doesn't really do justice to Chris's receiver.   We hope he will send us some more video, perhaps under better conditions, and perhaps with some more SSB. 

As you can see from this message from Chris in mid-July, he is a busy guy.  We were pleased that he found time to build this receiver.  Chris wrote

Good Morning guys!
I spent my July 4 weekend and 1200 round trip miles heading up to Richmond to pick up two 50 watt decommissioned airport non directional beacons that I hope to get working on either the 630m or 2200m bands. I'll most likely just use the amplifier, power supply and matching sections as they are modulated CW which isn't permitted. 
At least I have a nice high current power supply, outdoor enclosure and inner workings. I was told one worked and one doesn't.
I got them off eBay and the seller is a television engineer in Richmond named Greg. He listens to Soldersmoke too and is a builder like I am.
He said these are government surplus from a place called Camp Peary in VA.

The DC receiver is still coming along, I've just been overwhelmed with things on my to do list as well as a new job (learning lots about  high power lasers) so I promise it will get done soon. 

Chris 

Here are a couple of pictures of Chris's receiver.  Thanks Chris, and Welcome to the Hall of Fame.     

 

Dave K5YFO's FB Texas SolderSmoke Direct Conversion Receiver

The pine board is key.  Frank Jones (W6AJF) would approve. FB Dave.    CW video above and SSB below. 

Dave writes:  

Bill,

After many diversions from the work bench I finally got the Solder Smoke Challenge Receiver to operate.  There were the usual problems with the audio amp but my main problem was a faulty trimmer in the BP filter.

 

I hope I’m in the first 100 to complete the project. 

 

Hopefully the attached videos make it.  One is a CW and the other is SSB. 

 

73 de Dave K5YFO

Robert Sutton's Amazing SolderSmoke Direct Conversion Receiver

It is amazing that Robert (who is not yet licensed) got this receiver to work.  Check out his homebew coil form.  Excellent work Robert.  Congratulations and welcome to the Hall of Fame.  

Here is a Dicord exchange with Robert.  I think we see the true homebrew spirit here: 

Hall of Fame Update: 95 Completed SolderSmoke Direct Conversion Receivers, and 7 Honorable Mentions. Total: 102 receivers as of September 19, 2025 0849Z. More receivers are being built.

Please let us know if you spot any errors, or if we have inadvertently missed anyone.  Don't worry about being late to the game -- the challenge continues.  All of the info is still available (see below). 

As of September 19, 2025  0849Z:

So far 95 completed receivers, and 7 honorable mentions.  Total Count:  102.       Receivers built in 16 countries.   

NE3U (KY4EOD)  Matt 

KQ4AOP       First ham signals ever heard! 

N9TD             Derek

AC3NG          Ryan

VK3TPM       Peter Marks  

W4KAC         Ken 

W4KAC         Ken built a second one! 

N2EPE           Erik

VA3NCA        Wayde    

KI5SRY          Mark -- Gears on PTO screw

 

KA1MUQ       Frying pan receiver

AA1N              Adam

ZL1AUN         Aaron -- Using SSB transmitter

W8UC             Never before homebrewed. 

VK4PG           Phil -- Nice case, "really pleased"

G7LQX           Working well, video of CW and SSB. 

KE2AMP        John     Spring on PTO screw -- great

N9SZ              Steve  nice receiver

KD9NHZ        Piotr  Nice one

KE8ICE          Calvin, Very cool receiver. 

 

WV3V              Jayson!  Got it done!

GM5JDG         Martin.    

KF8BOG          Jim:  A long struggle, but success.  

Chris Wales    Fantastic video.  

YD9BAX         Wayan! Homebrew transformer! 

N0NQD         Jeff 

WN3F              Roy -- Made new stickers! 

AB5XQ            Bill  

KB7ZUT          Andy  

AA1OF            Jer

VictorKees        Holland

KC9OJV           John -- Manhattan-style convert

WZ5M              1, 2 or maybe even 3 receivers!

K1KJW             Jim in Vermont

KC5DI              Dallas -- friend of WZ5M

Gary                 Australian -- Wooden PTO form

LU2VJM          Juan in Argentina

K1OA               Scott "Most fun in 50 years"

KC9DLM         Ben -- Had EFHW problems

PH2LB             Lex  Yellow, Glue Stick

AI6WR             David

G6GEV            Dave (It was a blast!) 

KC1ONM        Wayne  MakerLabs NH

KB1OIQ          Andy    MakerLabs NH

KA1PQK         Jay       MakerLabs NH

W1TKO           Mike    MakerLabs NH

K5KHK            Karl

SM0TPW         Mikael

KI7LKB           Brian (coat hanger tube)

M6CRD            Chris

W2DAB           Dave in NYC

W4JYK            Wes of VWS

KA4CDN          Mike of VWS

M7EFO             Adrian 

VK5RC             Rob

KD8KHP          Dave

VK1CHW         Chris

KA0PHJ           Brian

W0IT                Louis

W1PJE             Phil

W2AEW           Alan

KN6FVK          John (Barkhausen-Be-Gone Spray) 

VU2JXN           Ramakrishnan

AA0MS            Doug 

9V1/KM7ABZ   Paul in Singapore

VK2BLQ          Stephen

N3FJZ              Rick

Daniel               VE5DLD

Student 1          Student of VE5DLD

Student 2          Student of VE5DLD

Student 3         Student of VE5DLD

K7WXW          Bill 

NK3H               Mitch

KN4ZXG         Ted

WA1MAC        Paul

N4AVC             Chuck 

K3IY                 Kevin

N6ASD             Ashish in Bangalore

W1DSP             Rick

WD4CFN         Steve

KM5Z             Mike

KF5DAN         Dan

Fritz                 Fritz

N9OK              Joe

WA5DSS         Bill 

K0GDB           Grant

G0JNR            Shane Glow-in-Dark Coil Form

KK7BCO        Tobias

K2BVR            Bob

Robert              Sutton

K5YFO           Dave (Texas) 

KD4PBJ          Chris

KN4GAH        Chris -- EE perspective

F1GMA           Philippe 

W2TEF            Todd

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

Honorable Mentions: 

*AA7U            Steve No PTO

*VK7IAN        Ian -- No Manhattan boards 

*KC1FSZ        Bruce's build on a PC board

*CT7AXD       Graham -- different AF amp

* DL1AJG      Andreas 

* Matthew      Student of DL1AJG

* Arash           Student of DL1AJG 

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

Candidates for the Hall of Fame: 

SA5RJS              Rasmus

KA9TII               James

AA7FO              Chuck 

VA3ZOT           Tony  Surface Mount -- Honorable Mention? 

AB2XT             John (Done, just need the video)

KO7M              Jeff (Piper Cub)

VU2TUM         Puneit Singh

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

Bob K2BVR's FB SolderSmoke Direct Conversion Receiver

Bob K2BVR homebrewed a really nice SolderSmoke Direct Conversion receiver.  On his "Proof of Life" video we hear some nice SSB signals, some great CW signals (including N7DZ/6 POTA) and even the well-known tones of FT8.  FB Bob.  Congratulations OM!  Welcome to the Hall of Fame. 

Bob writes: 

Hi Bill,

I wanted to send you a quick note of thanks. I’m very grateful to the SolderSmoke Discord users for their help, and to you and KK4DAS for all of the work you’ve both done in developing this project and sharing it through your videos.

I’ve been making progress on my build and thought I’d share a little update. I ran into some challenges with the bandpass filter – it turns out that reducing the trifilar winds per inch helped improve the performance. I also fought with a shorted test fixture along the way, which made things more confusing than they should have been.

On the audio side, my first amplifier module is still giving me trouble. I hated not getting it fixed right away, but I’ll be coming back to it. I did have to add a 470uF cap to the power rail to control oscillation but I haven't added the 220 ohm resistor. I’m thinking about putting the different modules into their own boxes so that I can experiment with them more easily in the future.

Thanks again for all of the inspiration and guidance — I really appreciate it.

73s

K2BVR

 

Tobias KK7BCO's FB SolderSmoke Direct Conversion Receiver

Sounds great Tobias!   Congratulations -- Welcome to the Hall of Fame! 

Tobias writes: 

Bill, I have joined the few. 

You guys created a project that even I could build. Thank you for the journey!

Now I plan to make duplicates of some elements, and create some kind of a terrifying musical instrument. 

Perhaps a Theremin Tobias?  AKA Etherphone!  This was reportedly one of Neil Armstrong's favorites! 

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