DC Receiver: 100db Gain? Diplexer? VFO in a box?

Here is a progress report on Direct Conversion Receiver developments. Dual Tuned Circuit, Diode Ring with Diplexer, PTO VFO from Farhan's Daylight rig, two stage 49 db BJT AF amp with a transformer. It works very well. I discuss: Shielding of the VFO -- necessary or not? Why brass in the PTO? Do we really need 100db in a receiver, especially with ear buds? Sourcing the AF amplifier's transformer. Using W7EL's diplexer. (I think it has solved my Radio Marti breakthrough problem). Developing a DC RX circuit that can be built by students. I end with a bandsweep of 40 meters that includes CW, FT-8, SSB, and AM

World's Most Interesting Man on PTOs and Glue Sticks

 

I mean, if they are good enough for the Dos Equis guy, maybe we should give them a chance. 

(134) Glue Sticks! Chap Sticks! Paul Clark’s Dollar Store Permeability Tuned Oscillators - YouTube

SolderSmoke FOREVER! Archived in the WayBack Machine

 

There were recently some stories about an effort to put on the Internet Archive recordings and other material from the history of ham radio.  I am pleased to report that the SolderSmoke podcasts have been included in the new collection: 

https://archive.org/details/soldersmoke-podcast

They also archived the recordings of my contacts with the MIR space station (and other spacecraft) from the Dominican Republic in the mid 1990s: 

https://archive.org/details/MIR-shuttle-audio

I have also suggested that they find a way to archive all of Jean Shepherd's recordings about ham radio. 

Thanks to Kay K6KJN for putting our material into the archive. 

Listening on 40 with a Glue Stick PTO in a Direct Conversion Receiver; Some PTO History

Thanks to Paul WA1MAC for this idea.  He first shared it with us via the SolderSmoke mailbag in 2008! Sorry it took so long for me to try one Paul. 

The PTO itself is an old idea of course.  Here is an article from 1966: 

https://www.radioexperimenter.us/rm-1966-04/a-homebrew-permeability-tuned-vfo.html

OM faced the problem of having to keep track of frequency while turning the dial many times.  He was hoping to use a turns counter -- in 1966 we didn't have the San Jian frequency counters.  I note that his PTO looked a lot like the one KK4DAS 3D printed for me (using file from Farhan).  

And some background on PTOs: https://sites.google.com/site/randomwok/Home/electronic-projects/permeability-tuners-last-stand

Paul Clark's Dollar Store PTOs made with Glue Sticks or Chap Sticks

A few weeks ago Pete Juliano and I got some e-mails from Paul Clark about his use of Chap Sticks and Glue Sticks (acquired at a Dollar Store!) in Permeability Tuned Oscillators.

Dean KK4DAS, Mike KA4CDN and I had been experimenting with PTOs following Farhan's use of one in his new Daylight Again transceiver. We are also looking at simple circuits for use in Direct Conversion Receiver builds for high school students.

Yesterday, I noticed a Glue Stick on the floor under my bench. TRGHS. I built one of Paul Clark's PTOs and used it with the circuit from Farhan's Daylight Again rig. For the ferrous material, I just glued (!) a .5 inch toroid (I think it is #7 material) onto the moving internal part of the glue stick. For the coil I used a total of 9 turns of #20 wire, with a tap at 2 turns. You can see the results in this video.

I think it is really useful, a very nice way to get good frequency control using an item available in most super-markets (I bought two glue sticks at Harris Teeter yesterday!). This continues a long ham radio tradition of using household items for ham projects -- we started with breadboards.

 Some of Paul's coils: 

Some of Paul's data:

Here's the data I got in testing these on the NanoVNA:

Burt's lip balm

16t #24 insulated

brass tubing ferrule

80pf

9.93mhz-10.80mhz

3.21uh-2.714uh

Dollar Store PTO Forms in 3 sizes

Small Jot Glue Stick (8 for $1.25!)

1 3/8" of #30 enameled close wound

waiting brass tubing to fit cup

80pf

2.980mhz with no core, I'm waiting brass tubing to fit this one (we have no hobby stores around here anymore that stock the K&S music wire and brass tubing assortments)

35.65uh

Medium Playschool Glue Stick

36t #30 enameled

1/2" copper water tubing

80pf

2.96m-3.380m

36.13uh-27.72uh

Large JOT Glue Stick

1/2" copper water tubing

80pf

28t #24 insulated

4.995m-5.625m

12.69uh-10.00uh

How the Diode Ring Multiplies by 1 and -1 -- "The Secrets of the Diode Ring" -- Plus another Bandsweep with the DC RX

A deeper look into how the Diode Ring detector works: "the particular go of it." Here I rely on a wonderful diagram from the RSGB. This diagram clearly shows how in this circuit, the switching action of the diodes -- controlled by the VFO -- results in sum and difference frequencies at the output. This is amazingly illuminating. I then tried to build this actual circuit. It works, but I am also getting a lot of AM breakthrough from a local AM station (WFAX) and Radio Marti at 7335 kHz. I will try again. In any case, the diagram shows how the diode ring does its thing! I need to beef up the Band Pass Filter. I tuned around a bit on 40 meters -- you can listen. Students at a local high school have been trying to get the DC receiver I loaned to them going -- they may be confused by the intricacies of SSB tuning. I will see them next week.

Here is the RSGB diagram that reveals the secrets of the Diode Ring.  (Now that could be the title of a book or movie.  I claim the rights to that!)  Click on the image for a better view. 

How to Tap an Aluminum Heat Sink: Pete Juliano Shares Tribal Knowledge

This is a SolderSmoke Classic:  Pete Juliano N6QW coached me on how to tap (put screw threads)

a piece of aluminum.  This is an important homebrew skill that -- as I demonstrate -- is 

easy to screw up (no pun intended).  Thanks to Pete for sharing this tribal knowledge. 

This video has been quite popular.  It has been viewed more than 33,000 times since 2014, and there are 35 comments attached to it.  

Thanks Pete! 

Adding a Diode Ring to the Direct Conversion Receiver, And How the Diode Ring Works

I take a look back at Wes Hayward's classic DC receiver from the November 1968 QST.

I then try to describe how diode ring mixers work ("the particular go of it") using Alan Wolke's excellent YouTube description as my base.

I present some drawings that I did that use the "crossed diode" diagram as the start.

I also discuss interference from Radio Marti's 250 kW transmitter on 7335 kHz in Greenville NC.

Finally, we listen to the receiver a bit.

Alan Wolke's Diagram

Wes Hayward's 1968 DC Receiver

Tim Hunkin's "The Radio Set" Drawing, and The Secret Life of the Radio (Remastered)

 

Click on the image for a better view. Click here for the whole drawing: 

https://www.secretlifeofmachines.com/secret_life_of_the_radio_set.shtml

I really liked this, and there is a lot more like it on the site of Tim Hunkin, the fellow who made all the great Secret Life of Machines shows.  His site: https://www.secretlifeofmachines.com/index.shtml

They remastered the show about radios.  It is worth watching: 

https://www.youtube.com/watch?v=LMxate9gegg

Thanks Tim! 

The Workshop and Bench of the QRP Home Builder, Todd VE7BPO

What a treat!  We have been learning so much, for so long from Todd VE7BPO.  I was really pleased to have this look at the workshop where all the magic happens.  

While my technical abilities are far inferior to his, I was pleased to see some scenes and some shelves that are similar to those that can be found here. 

Thanks Todd! 

Update on the Direct Conversion Receiver -- Now only 4 transistors

I took a new look at the receiver, did some measurements, and decided to take out the RF amplifier and the AF pre-amp. The receiver works fine without them, another indication that they were unnecessary. Line-up is now: Band-pass filter, Mixer, VFO, AF amp. I think there is only 49 db of gain in the entire receiver, but it is useable with an un-amplified speaker, and is a bit too loud on ear buds. Not bad for just 4 transistors. And I think we could do this with just 3 (no need for the VFO buffer).

Here is the AF amplifier I used:  

Sticker News (from Holland)

Lex PH2LB sends this really interesting Vice story about stickers and sticker culture.  Who knew?  The original article is in Dutch, but just hit the Google Translate button and Bob will be your uncle. 

https://www.vice.com/nl/article/wxnpp5/wie-zijn-de-mensen-die-overal-stickers-plakken

I shared with our Solder-Sticker Community these thoughts: 

Really cool Lex.   This reminds me that we need more stickers.  And maybe a new design.  The IBEW thing confuses Americans -- here it looks like a labor union thing. 

The Color Burst Liberation Army logo (below) is one possible element that we might want to include.  I think our new stickers should exhort people to DO something:  

"BUILD A SHORTWAVE RECEIVER!" 

"LIBERATE 3.579 MHz!"  

"MELT SOLDER!"  

"RESIST FT-8!"

"JUST SAY NO TO SDR!"    

Things like that. 

Thoughts?  Discuss.  

Bandsweep with the New Homebrew 40 meter Direct Conversion Receiver

It is inhaling nicely but some improvements are still pending. Click on the video above to see and listen to the bandsweep done on 40 this morning. 

-- The front end consists of capacitive divider input impedance matching circuit, followed by one LC circuit and an FET RF amp.  

-- The VFO is a super-simple Colpitts design by Farhan.   The two feedback capacitors do double duty in the LC tan circuit.  

-- I am using an old variable capacitor instead of the PTOs that we have been experimenting with.  

-- The mixer is singly balanced using one trifilar toroid and two diodes.  We have found out that even with these three simple devices, there is significant variation in how people connect them to VFO, RF in and audio out.  I think we have found the best way to do this:  Be sure to put the VFO on the primary of the transformer, and let this signal turn the diodes on and off. 

-- For the AF amplification, I have one FET, followed by two BJTs.  I have a small audio transformer between the speaker and the final AF amp.  There is plenty of audio. 

You may wonder why, after all the SSB superhet transceivers, I am building a simple Direct Conversion receiver.  Well, we hope to help a bunch of high school kids build one, so we need to be really familiar with how it works.  And I find that as simple as it is, there is still a lot to learn in a project like this. 

A Bout of Direct Conversion-ism in Northern Virginia -- DC Receivers Under Construction

There I was, minding my own business,  when suddenly I was dragged into the construction of Direct Conversion receivers. 

Here is a video about my latest effort.  But I feel the urge for more simplification -- I may go back to the seminal DC receiver designed by Wes W7ZOI and presented in the November 1968 issue of QST.  It is on page 15 here: https://worldradiohistory.com/Archive-DX/QST/60s/QST-1968-11.pdf

SolderSmoke Podcast #130 Feb 5, 2011 Trivia Questions! Recorded on a D-104! Heroic efforts to Suppresssss Ssssibilant SSSSs

February 5, 2011

For many reasons, this is a pretty amazing SolderSmoke episode. We presented some radio-electronic trivia questions. This is the one where I used an Astatic D-104 microphone to record the show. I even describe putting Starburst candies, Chicklet gum, and even Duct Tape on my teeth in an effort to get rid of the sibilant S problem. This was truly heroic podcasting my friends! There is lots of other great stuff in this one. Maria arrives in the shack with both Tyson the cat and Cappuccio the dog! Lots of space talk. The story of Grote Reber's name. Much more: Some important trivia questions (answers will be given in the podcast): What is the connection between radio amateur (and pioneer radio astronomer) Grote Reber and world famous astronomer Edwin Hubble? In the world of radio-controlled helicopters, what is "TBE"? In Britain they have radio "rallies," but at one time they had hamfests." When did this happen? Only one terrain feature on Venus is named for a man. He is man of radio. Who is he? What music did Neil Armstrong listen to on his way to the moon? Plus: -- The Air and Space Museums -- Our music -- The SolderSmoke D-104 -- NASA asks for our help -- Telescope repairs -- A BFO for the Trans-O -- Back on Echolink MAILBAG! Please send reports on the D-104 audio!

Open Circuits: Cutting Open Components for a Look inside -- First Chapter Free

 

Bob KD4EBM sent me this: 

“…. Eric Schlaepfer (@TubeTimeUS) and Windell Oskay (co-founder of Evil Mad Scientist)’s latest book, Open Circuits, is a celebration of the electronic aesthetic, by literally opening circuits with mechanical cross-sections, accompanied by pithy explanations and illustrations. Their masterfully executed cross-sectioning process and meticulous photography blur the line between engineering and art, reminding us that any engineering task executed with soul and care results in something that can inspire feelings of awe (“wow!”) and reflection (“huh.”): that is art. …”

https://www.bunniestudios.com/blog/?p=6558

I saw on Hack-A-Day today that the first chapter of the book is available as a free download: 

https://nostarch.com/download/OpenCircuits_Chapter1.pdf

Many of our favorite parts are dissected in that chapter.  The innards of a ceramic disc capacitor, for example, are shown above.

Thanks Bob! 

Talking about Homebrew Radio with the Williamsburg Virginia Radio Club

It was very nice to talk to Dino KL0S and the Williamsburg area radio club.  Thanks Dino! 

IGY on Hack-A-Day

https://hackaday.com/2022/09/20/igy-the-year-we-all-got-along/#more-553080

Nick's "Shelf-17" Al Fresco Homebrew Transceiver -- Frank Jones Would Approve!

This is a really wonderful video from Nick M0NTV.  

Some reactions:

 

-- Wow, a real celebration of Al Fresco!  And of the wooden chassis -- Frank Jones would be so pleased. 

-- Nick's description of the tales of woe caused by metal boxes is right on the mark, as is his description of the benefits of leaving the circuitry visible.  He's right -- this is an art and science kind of thing. 

-- That's a shelf, but it is FAR from being a shelf of shame! 

-- I am jealous of the S-meter.  I may need to include one of those in future rigs. 

-- Great to hear the shout outs to VK3HN, ZL2CTM, and N6QW -- we are are indeed the IBEW! 

-- I think we can see the N6QW influence in Nick's decision to use a steerable filter/IF amp board.  FB. 

-- I liked hearing Helio PV8AL in Boa Vista.   When I was building simple Direct Conversion receivers for 40 meters, I knew that I had it right when I could hear Helio's roosters in the morning! 

Be sure to watch this video, and to subscribe to Nicks Channel: https://www.youtube.com/c/M0NTVHomebrewing

He has done many other videos providing more details on the various stages that make up this rig. 

I hope to work Nick on 17 HB2HB soon. 

Thanks Nick! 

The James Webb Space Telescope -- Background Video and Update Article

The Scientific American video (above) has some really interesting info on how they built the JWST and what its capabilities are.  For example, they tell us that it could detect the heat from a single bumble bee at the distance of the surface of the moon.  How the mirror was made, and how it is adjusted in space is really amazing. 

The Scientific American article provides a good, balanced view of how the initial results from JWST are calling into question the basic models of cosmology: 

https://www.scientificamerican.com/article/jwsts-first-glimpses-of-early-galaxies-could-break-cosmology/