SolderSmoke Podcast #243 -- HI7/N2CQR, uBITX mods for 10 meters, High-School Direct Conversion Receiver Project Launched (Success!) Mailbag

 

DC RX and one of the PTO boards we built as demos last night. 

February 10, 2023

SolderSmoke Podcast #224 is available. 

http://soldersmoke.com/soldersmoke243.mp3

Video here: (32) SolderSmoke Podcast 243 (video) Hi7/N2CQR, uBITX, Success with High School Receiver Project - YouTube

Pete N6QW had technical difficulties this morning.  He insisted that the show must go on.  Pete will be back for the next episode. 

 

Travelogue: 

Bill in the Dominican Republic for all of January.  

HI7/N2CQR  Eastern tip of the island. uBITX and dipoles. 

20, 17, 10.  CW and SSB.  SSB was tough and I had reports of RF getting into the signal.

Went to CW. 

Worked VWS Mike KA4CDN, and Walter KA4KXX on 20CW.

Finally moved up to 10 CW.  Lots of contacts. Even though uBITX very QRP on ten.

I am modifying the uBITX now.  

Copper tape shielding to keep RF out.

 Low power out not the fault of the IRF-510s.  The problem is the 2N3904s.

Will replace with 2N2222 in To-18 cans.

Dean KK4DAS putting KD8CEC software into Arduino.  I gave up.

Who sent me this orphan uBITX?

SolderSmoke Shack South in final phase of construction.

 

SHAMELESS COMMERCE DIVISION:

Patreon!

Bezos Shopping!

 

DC Receiver Project

Local High School radio club. 

Simple:  Like Herring Aid 5 and Wes’s original.

Farhan’s four stages:

BP Filter, Diode Ring, PTO, AF amp. 

Simple Colpitts PTO SURPRISINGLY STABLE.

Simple and easy.  No chips.  No complicated circuits.

Guys have helped test out the design:  Rick N3FJZ, Walter KA4KXX,

Daniel VE5DLD, Stephen VK2BLQ and others. 

First session last night:  We demonstrated build of the PTOs.  

They worked (thank God).

 

Open Circuits book.

Envelope Detection Controversy

Save the Antenna – Book “Losing the Nobel Prize” K1JT

 

MAILBAG

--Dean KK4DAS 10 meter DSB!  Tiny SA ULTRA! FB

--John AC2RL on Elmer W3PHL DSB guy

--AC3K reports inventor of Fender Stratocaster guitar was a ham: W6DOE

--AF8E was doing POTA.  I worked him. He said my rig had presence. FB

--Alain F4IET FB DSB rig with mic in Cigar can!

--Daryl N0DP worked him on SSB.  He is homebrewing

--Steve N8NM was in for repairs but is on the mend.

--Rick G6AKG working with sub-harmonic mixers and logic chips

--Paul HS0ZLQ Built DC receiver but looking for something else to build. No DSB!

--Steve AB4I – Coherer, Jagadish Chandra Bose, and Marconi

--Eldon KC5U    Worked VK5QD right after me and mentioned SolderSmoke FB

--Todd K7TFC is building the DC RX.

--Tony G4WIF and Ian G3ROO using automotive relays for antenna switching. FB.

--Dave WA1LBP Great to hear from my fellow Hambassador (Okinawa)

Older post comments:

--Scott VO1DR was also in CF Rockey’s class! (Blog comment)

--Aurora Aug 4, 1972: Twelve people shared memories.  (Blog comment)

--Will WN1SLG Googled novice call and was led to my Novice log.(Blog comment)

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? 

Rick N3FJZ Completes Build of High-School Direct Conversion Receiver Project -- LISTEN!

Rick N3FJZ has completed his the direct conversion receiver that we will soon be building with students at a local high school.   See video above. 

We are hoping that a number of people will build the receiver as we designed it.  Some folks have sent us versions of the receiver that they have built, but these versions often include significant deviations from our design, rendering them less-than-useful in checking our work.  Rick built it just as we prescribed.  His build is very useful in confirming the validity of our design.  So if you are working on one of these receivers, I would encourage you to -- for the moment -- dispense with innovations and build it the way Rick did:  as per the design we have been using. 

We know that our design is not perfect.  But we have decided to stick with it because it is very simple and very easy to explain.  Examples:  We know there is an impedance mismatch between the mixer and the AF amp.  But fixing this would introduce complexity that we want to avoid.   And the receiver works fine with the imperfection.   We know that a push-pull AF amp would probably work better than the one we have.  But we do not want to have to explain push-pull amps, biasing schemes, and PNP transistors in this short introductory course.  So we stuck with three common-emitter AF amp circuits and an 1K-8ohm transformer. 

Rick did a really excellent job not only in building this receiver, but also in documenting it.   His diagrams and drawings are really superb.  We will probably use these in our presentations to the students: 

http://www.remmepark.com/circuit6040/SolderSmoke-DCR/SolderSmoke-DCR.html#AUDIO_AMP

We will keep all of you informed on the progress of this project.  We will begin this week.  But if you are still working on the receiver, please send us your work,  even if it comes in after we begin the course.  

Thanks Rick! 

To Re-Cap or Not to Re-Cap -- Curious Marc on the Electrolytic Controversy in Ham Radio

A while back I got some fairly acerbic feedback when I DARED to suggest that perhaps it would be a good idea to replace the old electrolytic capacitors in ham radio equipment.  It was as if I had attacked motherhood and apple pie!   

Yesterday I was looking at CuriousMarc's YouTube channel and I came across the above video.  While I had been in the preemptive replacement camp, Marc makes a good case for leaving some of the old caps in place.   The fact that the electrolytics usually are open when they fail, and that there are fuses in the power supply to protect the transformers,  are important points.  His admonition not to replace electrolytics with tantalum caps (which fail closed) was also very useful. 

OK, my flame-proof suit is on! 

CuriousMarc (AJ6JV) Goes to a Hamfest

Jean Shepherd once said that all of us at one point come to a cross-roads in our lives -- one road leads to success, the other to ham radio flea markets.  

As I watched this, I realized that CuriousMarc sounds like a ham.   Sure enough, some Googling revealed that his real name is Jean-Marc Verdiell and his ham radio callsign is AJ6JV. 

I knew Marc was one of us when, in the video, he opens up the teletype.  He says that the seller claimed that it still worked.  But Marc comments that he hopes that this is not true, so that they will be able to troubleshoot and fix the device.  FB.  That's the spirit.  

We are really lucky to have someone as successful and creative as Marc in the ranks of ham radio operators.  

Be careful with the high voltage Marc!  

Checking Into the Vienna Wireless Pow-Wow Net after 23 Years!

 

I used to check into this net with my HW-101 from 1996-2000.   Last night I fired up my uBITX, hookied it up to my CCI .1 kW amp, and tuned the 75 meter doublet for 10 meters.  Bill AF4LL (Mr. 10 Meters) was net control.   Mike AE4R was also on frequency -- he was there the last time I checked in too.   It was fun.   

The QSL card shows the transceiver with the LiPo battery that was powering it. 

Direct Conversion Receiver Bandscan -- 40 Meters early on a Thursday Morning -- With W1AW/4

I superglued a San Jian frequency counter to the front panel of my High School Direct Conversion receiver.  Then I tuned it through the 40 meter band.  You can hear the W1AW/4 station.  And several SSB stations.  

Hammarlund HQ-100 Misidentified in 1963 FCC Film

Oh the indignity!  It appears at 7 minutes 16 seconds in this FCC film.  It is clearly an HQ-100, but the FCC subtitles identify it at an HQ-110.  It is clearly an HQ-100 ( the model without the clock). 

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

As the owner and operator of what must be one of the few remaining HQ-100s, I feel obligated to defend the reputation of this fine piece of shortwave gear.   

How many of you have HQ-100s?  

Curious Marc's Lab and Workshop

This is the guy who has done all the amazing videos on the Apollo communications systems.  And a lot more. This look at his lab is inspirational.  

There is so much to see here.  But a couple of things really caught my attention: 

All of the RF electronics in the Apollo spacecraft was made with discrete components -- the only chips in the spacecraft were in the computer.  And in the Apollo systems, they welded the discrete components in.  No soldering.  Welding.  That's hardcore.  That is how they got to the Moon.  

Curious Marc's YouTube channel:  https://www.youtube.com/@CuriousMarc

Rick N3FJZ Builds the Mixer for the High School Direct Conversion Receiver

Wonderful progress from Rick N3FJZ.   Having completed the PTO,  Rick went on to build the diode ring mixer and diplexer.  (See video above.)  He then connected these to boards to a band pass filter and an AF amp from previous project.  And wow, the resulting receiver sounds really great!  I think it sounds better than the ones Dean and I have built.  

-- It will be interesting to see how Rick's receiver sounds with the very simple AF amplifier that we are using.  

-- We need to get Rick a coil form for the PTO variable inductor! And getting him the PTO form will allow him to dispense with the varactor circuit (which, I must say, is pretty cool). 

-- In the PTO, for the coupling capacitor (C15) , I now have a 260 pF NP0 cap.  But your .1 uF ceramic disc seems to be doing just fin.  So maybe we don't need the NP0. 

-- I'm glad that Rick grounded the brass screw.  Without that, the hand capacitance effect is bad. 

-- I think results will be much the same with the dual tuned circuit bandpass filter that we use.   But it will be interesting to see if Rick's triple tuned circuit helps with AM breakthrough (I think I heard Radio Marti when Rick tuned to the top of the band). 

-- I haven't had a hum problem and I don't think Dean has either.   Dean is running his on two 9V batteries.  Maybe that would take care of the hum.  Our PTOs are completely Al Fresco! 

-- The Traders Net sounds like fun!  

Thanks Rick!  73 

Hugo Gernsback -- Was he Like Wayne Green?

"The Electrical Experimenter" sent to me by Nick M0NTV reminded me of Hugo Gernsback.  Many of the radio books I have on my shelf have his name on them.  He played a big role in early radio and television, and in science fiction. Check out the Wikipedia article on Gernsback:  

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

I see similarities between Hugo Gernsback and Wayne Green.  What do you guys think?   

Gernsback's TV goggles in 1963 

That's Gernsback watching TV in 1928

N3FJZ Builds PTO for High School DC Receiver

Rick N3FJZ has stepped forward and is building the direct conversion receiver that Dean and I have been working on.  This will be big help in our testing of the receiver.  See above for the video report on his build of the PTO stage. 

When I saw this, I found myself thinking two things: 

1) Those really are "rigs." 

and

2) I am not alone! 

Years ago, I was having a tough day on 40 meters.  The Waterfall Policemen were gleefully attacking my admitedly less-than-perfect SSB signal.   Unbeknownst to me, someone out there was listening, and listening with a homebrew receiver.  A receiver with a PTO.  It was Rick N3FJZ.  He made my day when he sent this video: 

https://soldersmoke.blogspot.com/2015/02/parasitic-anguish-on-40-then-homebrew.html

Here are the other blog posts on the amazing rigs of N3FJZ here: 

https://soldersmoke.blogspot.com/search?q=N3FJZ

More to follow, both on Rick's receiver and on the work of other intrepid builders. 

Thanks Rick. 

"The Electrical Experimenter" -- A Treasure Trove of Inspiration

Oh this is really phenomenal.  Nick "the Vic"  M0NTV is on the mend from some routine surgery.  While mending he found this 1915 issue of Hugo Gernsback's "The Electrical Experimenter."  I just spent a few minutes quickly going through it and I can see that this is a treasure trove that could keep us -- the modern day electrical experimenters -- busy for a long time.  

-- We see Signor Marconi in Italian military uniform (I never saw that before).  

-- There is mention of successful DX reception of the station in Arlington Va. (just down the road from me).  

-- There is a an article about the radio station of T.O.M -- Hiram Percy Maxim.  

-- There are detailed maps of Mars, complete with the canals. 

And there is a lot more.  

Above all, I think what stands out from this magazine is the homebrew spirit,  the notion that we can and should build our rigs ourselves, and seek to understand them. 

Below is the whole magazine.  Please take a look and use the comment section below to point us to passages of interest to the electrical experimenters of today.  

Thanks Nick.  Your e-mail came during a discouraging period filled with a few "tales of woe."  The magazine really lifted my spirits.  

Here it is: 

http://soldersmoke.com/EE-1915-10.pdf 

Update on High School Direct Conversion Receiver Project + .asc File

So far, in response to my recent request for testing,  no one has stepped up to build the DC receiver Dean KK4DAS and I are testing out.  We did get a couple of comments explaining why guys are opting not to help, but so far no other builders are actually melting solder in response to our recent request. 

So Dean and I decided to each build second versions of the receiver.   That will bring the total finished build population to 4.  I finished my second version yesterday.  Picture above.   It works great.  

One change:  The emitter resistor on the final AF amp was too low in value.   The transistor and the transformer were getting hot.  I switched from 10 ohms to 100 ohms and the problem disappeared.  I have made the change on the LTSpice Schematic.   Here is the .asc file (I hope!) : 

http://soldersmoke.com/DCRX.asc

Dean posted the .asc file (and some other info) here: 

http://bit.ly/3WAFfLI

If you have trouble accessing that file, please let me know and I will try to e-mail it to you.   In any case the schematic appears here: 

https://soldersmoke.blogspot.com/2023/01/a-call-for-builders-please-help-us-test.html

You will notice that this Spice schematic actually works!  The PTO turns on, and I put a simulated RF signal at the antenna port.  Audio appears at the output.  

Time is getting very tight.  Dean and I will begin presenting this project to the high school students on February 2.  So it is not too late to help. But helping is, of course, strictly voluntary -- if you are reluctant to build this thing, DON'T!   

My HI7/N2CQR QSL Card

My fellow Vienna Wireless Society Member Ron WA6YOU is a real expert collector of QSL cards.  He was rightly critical of a very crude homebrew QSL that I made a while ago.   So when I got back from the Dominican Republic I decided I had to clean up my act.  Some Googling, some printer ink, and some cardstock later, I came up with the above.   I kind of like it -- it looks better (believe me!) than my earlier effort, but it retains an element of homebrew (I kind of made it myself).  

The picture is of Juanillo Beach, the beach we use when in Cap Cana.  This one was filled out for Mike KA4CDN, who was the only Vienna Wireless Society member I contacted from HI7.  

I made about 38 contacts from HI7.  If anyone out there worked me and wants a card, my printer is at the ready!  

To make the card, I used:  https://www.radioqth.net/qslcards

A Call for Builders! Please help us Test this Receiver! Please Build this Receiver!

 

This is the Direct Conversion receiver that Dean and I have built.  We plan to have students at a local high school build it, starting in early February.   We would like to have some others build it, to make sure that the design is re-producible without problems.  

Please build this receiver!  But we ask that you build it exactly as per the schematic above and below. Innovation can come later -- for now we just want to make sure this thing works, that there are no errors in the schematic, and that it can be built by the students with minimum woe.  Thanks in advance! 

Dean or others with 3D printers may be able to supply the plastic form for the PTO inductor.  

We know of one other builder, but he is having some trouble.  We would like to confirm that this design is sound.  

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

Above is the screenshot of the LTSpice model of the 40 meter Direct Conversion receiver that Dean KK4DAS and I have been working on.  I will post a larger scale version of the picture below.  Click on the images for a better view.  Comments welcome.  Please let us know if you find any errors or mistakes.  Realize that we wanted to keep this all simple, discrete, and entirely analog. 

Here (I hope!) is the net list for the LTSpice model: 

http://soldersmoke.com/DCRXLTSPICE.net  

First, one of the surprising things about the LTSpice model: IT IS ALIVE!  I never had a VFO or PTO actually turn on for me in LTSpice.  This one did!  So I just connected the PTO to the Mixer and the receiver works in LTSpice.   I just put an RF signal at the receiver input, and you can see the resulting AF across the 8 ohm resistor at the audio amp output.  I was even able to calculate the precise frequency of the PTO:  7078 kHz.  As in the real world, in an effort to stabilize the frequency, I changed the capacitors to NP0 in LTSpice.  Very cool.  Dean joked that all we need is a way to get RF in and audio out and we will have made an SDR receiver.  

About the receiver:  

--  Four stages that will be built by students Manhattan-style on four copper clad boards: Bandpass filter, diode ring mixer, Permeability Tuned Oscillator (PTO),  AF Amplifier.  

-- The bandpass filter is a simple dual-tuned circuit device based on the info on the QRP Labs site.  (Thanks Hans!)  We out a 10k pot as an RF gain control between the antenna and the filter. 

-- The mixer is a standard diode ring.  We included a diplexer at the output using a circuit from the famous W7EL  Optimized transceiver. (Thanks Roy!) 

-- The Permeability Tuned Oscillator is a very simple and very stable Colpitts design developed by Farhan VU2ESE.  We added a simple FET buffer using the circuit in Farhan's Daylight Again rig.  (Thanks Farhan!) 

-- The AF amp is a very simple three transistor amplifier based loosely on designs from Forrest Mims and from the Herring Aid 5 receiver. Both these designs use just two stages -- we added a third and put an AF gain pot between the first and the second stages. There is an impedance mismatch between the diode ring and the AF amp, but we found that most of the proposed solutions were more trouble than they were worth, so we left it as is.  

--Thanks to Wes W7ZOI for his November 1968 QST article on the solid-state DC receiver. Wes's article inspired our efforts.  

Dean and I have both built these receivers.  They work very well.  Dean has even decoded FT-8 with his. We used Radio Marti at 7355 kHz to test for AM breakthrough -- with the diode ring, the diplexer, and the RF gain control we were able to bring the AM breakthrough down to acceptable levels. You can see many videos of my receiver in action over on my YouTube channel:  (355) SolderSmoke - YouTube

Here is a larger image of the schematic (click for a full view): 

And here is a nicer schematic done by our friend Walter KA4KXX: 

Open Circuits: The Inner Beauty of Electronic Components

I was not going to buy this book.   But then, Elisa and I were in a book store and there it was.  I decided to take a look.  I opened it to a random page:  2N3904.  TRGHS.  Sold.    

It is really interesting. 

You can order yours through the Amazon Search block in the right side column of the blog.  

https://spectrum.ieee.org/open-circuits

SolderSmoke Re-Play: Goggle EMBRACES Morse Code: Gmail Tap

Wow!  CW finally gets some respect from the Silicon Valley guys!  There is actually a Vibroplex bug in this video.  And they note how USEFUL this will be for those afflicted with Fat Finger Syndrome (Pete's Disease). FB Google!  TNX! 

I was feeling kind of bad about the fact that there was one year in which we didn't do something special on the first day of the fourth month.  That year was 2012.  But looking back, we kind of did! The very next day, we posted this really awesome video from the folks at Google:

 https://soldersmoke.blogspot.com/2012/04/google-cw.html 

 

A True Measure of a Jean Shepherd Fan: Did You Fly One of His Ornithopters?

 

I did.  Shep had as a sponsor the maker of a flying bird.  It was a wind-up ornithopter powered by a rubber band.  It was kind of like the one in the picture, but I remember mine as being yellow.  My dad got it for me after hearing Shep talk about it on his program.  Wow, what a sponsor!  Shep must have made DOZENS of dollars from that deal! 

It looks like Shep was pitching this thing in 1972, which was my first year in high school.   

https://www.flicklives.com/index.php?pg=331&recno=5619

It took some coaxing and adjustment, but it did fly. 

My thinking about this was prompted by an article on Hack-A-Day:  

https://hackaday.com/2023/01/16/flappy-bird-drone-edition/

(I want to hear that program about the wedding on 75!)

EXCELSIOR!

Working Walter KA4KXX from Hispaniola

 Walter KA4KXX in Orlando has been a prolific builder of rigs for many years, and has been a great friend of SolderSmoke:  Here are some of the SolderSmoke podcasts and blog posts in which Walter's solder melting was mentioned: https://soldersmoke.blogspot.com/search?q=KA4KXX

As we approach the end of our current stay in the Dominican Republic, I could not miss out on the chance to work Walter with his homebrew rigs.  Even though the space weather was stormy, and my dipole was droopy, we arranged to meet up on the high end of the 20 meter CW band this morning.   See the results in the video above.  A solid QSO with Walter.  He says it is HB2HB, but truth be told I was on a uBITX that was built more by Farhan than by me.  But this was a great contact.  Walter started with a 50W rig, then switched to his 3 watt rig with a DC receiver.  FB

Here is the e-mail I received from Walter after the QSO: 

Dear Bill:

Many thanks for the great video, and when

you return to Virginia look for your mailman

to bring a postcard from me!

Just after your phone call this morning I scanned

the band from 14.025 to 14.300 and heard only one

SSB QSO at 14.347, and even now I only hear

a half dozen SSB signals, so that makes what

we did even more amazing. 

The first photo below is my 3.5 watt NE602 direct conversion 

rig which is about 2 years old.  The transmit signal is created

by putting a 3 MHz VFO signal into an NE602 mixer with an 

11 MHz crystal, so the rig can receive CW and SSB from 

14.025 to 14.300 and can transmit CW anywhere in that range

with good frequency stability. 

The bottom photo is my new full break-in CW 50W rig which 

I just put on the air about a week ago and is still in the finalization stage.  

I am not yet happy with it, but then again I am more particular

now than I used to be.  It is really a trans-receiver with a single 

conversion superhet receiver at the bottom of the board using 

an NE602 pair with a 3-crystal 4 MHz 900 Hz bandwidth filter, 

and a single 10.080 crystal VFO which is tuned with a polyvaricon

for operating between 14.061 and 14.068 MHz.  

At the top is the VXO transmit section using a pair of 14.070 

crystals pulled down into the operating range.  This signal

is buffered and amplified to about 500 mW which is all that 

the MRF101 RF Power Amplifier needs.  Visible behind the

board is an AC-powered 24 VDC switching power supply which 

is connected in series with the 12 VDC battery to 

power the final stage with about 36 VDC.  The main 12 VDC is 

provided by a bench power supply which is not in the photo.

In both rigs the morse code key is the microswitch 

at the lower right corner.  (Way more handy and elegant 

than your key, I might say?)

This morning each of these rigs was connected to its own

end fed half wave antenna, one in my backyard 

and the other on the side of my house.  My antenna analyzer

shows them to be essentially equal, but my 50W rig does

not like one of them at all.

Making our international homebrew-to-homebrew contact 

today was a terrific ham radio experience, so thanks for all 

you do!

73,

Walter 

KA4KXX

Orlando, FL