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

Working Vienna Wireless Society member (KA4CDN) from Hispaniola

We'll be heading back to the States soon and I was feeling guilty about 

not having worked anyone from my home club (the Vienna Wireless Society). 

On Wednesday night I Zoomed in to the club's Maker group -- this made me want 

to make at least one contact with the club.  Plus Walter KA4KXX  in Orlando has 

been trying to set up a sked on 20... This morning I saw that the SFI was up above 200. 

I lengthened the dipole so it would resonate on 20 meters (on this trip it started on 20, went to 17, back to 20, down to 10 and now, back to 20!). I worked one station on SSB, then sent a text to the club's DX spotter group, saying that I would be calling CQ on 14.060 MHz.   Soon I got a call from club member (and Maker) Mike KA4CDN.  We had a nice QSO.  Thanks Mike (video of our QSO above). I will try with Walter tomorrow.  

 

On Ten Meters with a uBITX from the Eastern Tip of Hispaniola

On ten from HI7.  Cluster spots, DX, CW, and the Reverse Beacon Network. 

 

SolderSmoke Re-Play: Shep tries to build a Heising Modulator -- Shep on Parasitics and Troubleshooting: "That way madness lies"

You guys really have to listen to this.  This is culturally important.   

In this 1965 radio broadcast, Jean Shepherd describes his teenage struggles with parasitics and other technical problems in his homebrew 160 meter transmitter.

He describes the sound of parasitics on a signal, saying that they sound as if the signal is being attacked by "debauched erotic locusts."

He really nails it in describing the scornful, dismissive tone that many hams use in telling their fellow radio amateur that there are problems with his signal. ( I have recently been on the receiving end of this kind of treatment.)

He observes that no one is more worried, "than a man who has built something and can't get it to work." Indeed.

During a date with a girl from his high school, he is so obviously preoccupied with his transmitter trouble that she tells him that something is wrong with him and that his mother "should take him to a doctor."

And he describes the joy that comes when you figure out the problem and get the thing to work.

The REALLY good stuff begins at about the 25 minute point.

http://ia310115.us.archive.org/2/items/JeanShepherd1965Pt1/1965_01_29_Ham_Radio.mp3

Shep was quoting from King Lear: "O, that way madness lies; let me shun that; No more of that."  In other words: "BASTA!"  

EXCELSIOR!