"The Build Is the Initiation" -- KQ4AOP Offers Encouragement and a PTO Coil Form for Receiver Builders

Scott KQ4AOP put a comment on a recent SolderSmoke Blog post that I found especially encouraging and apprportiate. He was writing about his experience building the High School Direct Conversion receiver.  

Scott wrote:

"This was my first receiver build and, it was great fun. When you finish the build and prove you are able to tune through the band, you are welcomed into the secret society! The build is the initiation. I am happy to print and ship the PTO if needed." 

The 3d printed form for the tuning inductor is often a show-stopper for prospective builders.  Scott offers to print out a form for you, and send it to you. 

Scott's mailing address is on his QRZ page.  His e-mail address is: streez55@gmail.com

 Thanks Scott! 

Here is a post I did early this year on Scott's receiver: 

https://soldersmoke.blogspot.com/2024/02/scott-kq4aop-successfully-builds.html 

Here are the SolderSmoke Posts about this project  (keep scrolling -- there are 41 posts!):

https://soldersmoke.blogspot.com/search/label/TJ%20DC%20RX 

My Receiver Doesn't Work Right! What Should I Do?

An early version of our DC receiver.  Note the tuning guide under the grey tuning knob. 

We prepared this for use by the high school students who were building direct conversion receivers. Unfortunately none of them got to the point where they would use this little article, but given the fact that a number of people are now engaged in direct conversion receiver projects, I thought it would be a good idea to post this here. Also, much of this applies more generally to receiver problems. 

My receiver doesn’t work right!

What should I do?

First, relax.  You will be able to get it to work.  The design is good, people around the world have built this receiver, and you will be able to get it to work.  But homebrew radio is not plug-and-play radio.  Sometimes a new receiver needs some tweaking, peaking, and coaxing. 

Realize that the 40 meter band has its ups and downs.  The downs usually come at mid-day.  The sun’s position high in the sky causes a build up of the D layer of the ionosphere.  This tends to absorb radio waves. So signals are often weak at mid-day.  Signals will be much stronger in the morning, and in the evening.

Can you hear the “band noise” when you connect your antenna?   This sounds like hiss or static.  Some of this is the result of thunderstorms in Brazil.  Some of it is from events far away in the cosmos. Some of it comes from the weed whacker down the block!  But if you can hear this noise, that is a very good sign that your receiver is working.  The signals you are looking for will be stronger than this band noise.

Where are you tuning?  Your receiver tunes from about 6.8 MHz (with the screw all the way our) to about 7.8 MHz (screw all the way in).  But we are only really interested in the ham frequency band between 7.0 MHz and 7.3 MHz.  Try to tune your receiver near the middle of the tuning range (with the screw about half-way in).  You should hear morse code from about 7.0 to 7.06 MHz.  Then you should hear strong digital signals at 7.074 MHz.  Tuning further up (screw going in) you should start to hear hams speaking to each other using Single Sideband.   At first they will sound like Donald Duck.

 Don’t worry about the Donald Duck speech!  Just carefully tune through the signal until you hit the spot where the speech sounds normal.  You may have to tune up and down a bit until you find the right spot.  Now you can listen. 

 If you tune further up you will hear Shortwave Broadcast band AM signals.  You will be able to tune them in.  Sort of.  But they will sound distorted.  This is unavoidable with this kind of receiver.  But you will be able to hear the hams on Single Sideband with no distortion.

Sometimes you will only hear one side of the conversation.  That is normal.  The other station may be either too far away from you, or too close to you.  You may be outside his or her skip zone.

One very obvious thing to check:  How is your battery?  Is it drained, or is it still at about 9 volts?   You may need to change it.

How is your antenna?   It doesn’t have to be fancy or elaborate.   33 feet of wire will do.  But it does need to be up in the air a bit.  And you need to have the 33 foot counterpoise wire connected to the ground (on the PC board).  With many pieces of consumer electronics antennas are kind of optional – the devices will often work without them.  Not so with ham gear.  Antennas are important.  If you are not receiving signals,  it may be because of your antenna.

SimpleX Super Superhet Receiver -- A Great Video from Mike WU2D

Here is another great video (and project) from Mike WU2D.  I'm a big fan of homebrew superhets.  And wow, Mike presents a band-imaging superhet!  Two bands for (almost) the price of one!  I have FIVE homebrew dual-band band-imaging transceivers around me.  Believe me, once you have the experience needed to build an SSB transceiver, a dual-bander is the way to go.  Five bands seems like a bit too much.  But two seems to be at the sweet spot.  

I wrote to Mike reminding him to talk about the sideband inversion problem.  This rig will invert the 75 meter signals,  but this is easily resolved by just shifting the BFO frequency.  I also pointed out that many of today's builders will be detered by the need to scrounge for parts.  Where oh where is the BOM OM? 

Thanks Mike! 

Challenge Accepted! Why we Designed the High-School Direct-Conversion Receiver the Way we Did

Dean KK4DAS's Beautiful DC Receiver

The folks over at Ham Radio Workbench have graciously accepted the challenge issued in our last podcast: that they scratch-build homebrew the 40 meter Direct Conversion receiver that Dean KK4DAS and I designed for local high school students.  We want to help our brothers over at HRWB.  For example, we may be able to supply a few of the 3D printed PTO coil forms.  Here is some background information on the project. 

Details on the project can be found here: 

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

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

Design Decisions in the Direct Conversion Receiver

Why did we do it this way?

In thinking about how to design this receiver, we had to make early design decisions on almost every stage.  Here are some of our key considerations.

VARIABLE FREQUENCY OSCILLATOR:

Normally we might have used a variable capacitor to change the frequency of this oscillator.  But variable capacitors are now expensive and hard-to-source.  Our friend Farhan in Hyderabad used a simple variable inductor for this purpose in his “Daylight Again” transceiver. The coil form for this part could be 3D printed.  A metallic screw would vary the inductance as it is screwed in and out of the coil.  

We also decided to use the same simple Colpitts oscillator circuit used by Farhan in his own high school direct conversion receiver.  This circuit is unusual in that the feedback capacitors are also the frequency determining elements (along with the variable inductor).  This simplified the circuit and reduced the parts count, and proved to be remarkably stable.

For the VFO buffer we used the simple JFET buffer from Farhan’s Daylight Again design.  

Based on suggestions from other radio amateurs, we developed a simple frequency readout based on the position of the end of the tuning screw  (how far in or out?).

We selected the 40 Meter band for this receiver because we thought it would be easier to get the VFO stable on this frequency, and because Farhan had built his receiver for 40 meters.

MIXER:

At first we hoped to use a simple singly-balanced mixer using two diodes and a single trifilar transformer.   But we found unacceptably high levels of AM breakthrough (mostly from Radio Marti on 7335 kHz) when using this circuit.  So we switched to a diode ring.  This required two more diodes and an additional trifilar transformer.   We believed the students would have great difficulty building and installing two trifilar transformers so early in their building experience.  So we used transformers that had been wound in Hyderabad by a women’s collective employed by Farhan, and developed a scheme for fool-proof installation of these transformers.

We also found that the mixer needed a diplexer at its output – this would provide a 50 ohm termination at all frequencies and would result in much cleaner action by the mixer and greatly reduced AM breakthrough from Radio Marti.   We used the same circuit used by Roy Lewellen W7EL in his Optimized Transceiver circuit.

BANDPASS FILTER: 

This was the simplest board in the project but it required the students to wind two coils on toroidal cores.  A simple dual-tuned circuit design would be sufficient.  We used component values from the QRP Labs website.  We showed them how to wind the coils, and made a video about the technique.  Students used a simple Vector Network Analyzer (Nano VNA)  to tune the filter.

 

AUDIO AMPLIFIER: 

We had to make several design decisions here.  First, we rejected the idea of using an IC amplifier like the ubiquitous LM-386. We wanted this to be a completely analog and discrete component experience. Then we rejected the idea of using a push-pull output circuit.  While this would have eliminated the need for an audio output transformer, it would have resulted in a more complicated circuit.  In the end we opted for three simple RC-coupled common-emitter amplifiers with an audio output transformer.  There was no feedback in these circuits.  We found there is a lot of gain (hFe) variation in the 2N3904 transistors that we used.  Care needs to be exercised in making sure that transistors of moderate (but not too high) gain are used.  

This AF amplifier chain probably presented a 1500 ohm impedance to the mixer (instead of the desired 50 ohms), but we think this problem may have largely been taken care of by the diplexer.  

We found some very small (one square inch) speakers that could be easily used in this circuit.

ANTENNA:

While the students could use a wide variety of antennas, we recommended a simple ¼ wave antenna with a ¼ wave counterpoise.  We thought that this antenna – of only 33 feet in length would provide good performance with low complexity, and would be well suited to the “upper floor bedrooms” from  which many of the students would be listening.  Also, this antenna would not require the use of coaxial cable or an impedance matching transformer. We made a video on how to build and use this antenna. 

POWER SUPPLY:

We opted for the use of 9 volt batteries.  This proved to be a safer and wiser choice that limited the kind of mayhem that could occur should a variable voltage supply be used.

Details on the receiver can be found here: 

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

May 29, 2023

Pil Joo's Homebrew Superheterodyne Ham-Radio Receiver

It is just very cool to see someone build a superhet and get it to work.  For so many years amateurs were told that "homebrew receivers are too hard."  Even simple regens or direct conversion rigs were sometimes seen as beyond the abilities of amateurs.  But here we see another reminder of this not being true.  Even a superhet -- which is a lot more difficult than a direct conversion receiver -- can be homebrewed by an amateur builder.  Three cheers for Pil Joo! 

He wrote on the SolderSmoke Facebook page: 

I finished my first super het receiver. It's for the 40m band. It consists of: bandpass filter, tuned amp, diode ring mixer, wide band amp, crystal ladder filter, wide band amp, then SA602 + LM386 combo. I learned tons as i put all the components. First two amps are my design. The third amp is bga2866. The bandpass filter is what i posted a few days ago. I planned to make another one but with 2.5db insertion loss i thought it was good enough.

The result is actually quite good. I can hear everything a local kiwisdr can hear. Now, I have lots of ideas about how i can improve, but that will be another radio.

Pil Joo

A 40 Meter Direct Conversion Receiver from M0NTV -- With some SolderSmoke Comments

Nick's video appears above. 

First, let me say FB Nick.   It is nice to see you making use of the AGC amp designed by Wes and Bob,  using the board from Todd's Mostly DIY RF, using a mix of homebrew pads and Me-Squares  from Rex, and finally the Franklin Oscillator that we spent so much time talking about on SolderSmoke.  

But here are some comments:  

-- I still don't think you need that RF amplifier in front of the mixer. And I suspect you would be better off without it.  We did not use one in our high school 40 meter project, and never missed it.  In fact, on one version of the high school receiver I even put in a simple 10k pot as an attenuator (no RF amp).  Even up on 20 meters, I do not have an RF amplifier ahead of the diode ring mixer on either of the Mythbuster rigs I have built.  Nick,  maybe experiment a bit more and try the receiver just going from the BP filter into the mixer and see what happens.  

Note that Wes W7ZOI DID NOT have an REF amp ahead of the diode ring mixer in his original 1968 40 meter Direct Conversion receiver (the one that launched the solid-state DC recevier revolution): 

-- The Franklin oscillator is an interesting, but complicated circuit.  The gimmick is, well, gimmicky.  Here is the thing:  You can achieve similar levels of stability using simple conventional, single transistor oscillators.  We dispensed with the variable capacitors, and used PTO--style variable inductors. They worked fine.  This Franklin oscillator still does seem to drift a bit, right?   I would ground the board to the inside of the metal box.    

I would also try putting all the stages on a single ground plane.  This might help.  

Charlie "Red" NJ7V Builds an Oscillator -- Manhattan Style

https://www.youtube.com/shorts/7t_E5N4CQxg

Red did a nice job building, then explaining, this 18 MHz crystal oscillator.   I especially liked his use of Manhattan techniques, and the way he explained his effort to make the new circuit work.  Too often builders expect a circuit to work right away.   This often doesn't happen, and the new circuit requires some troubleshooting.  Red did this with this circuit and got it working.  

Red has a nice YouTube channel: https://www.youtube.com/@RedSummitRF.  It is focused on POTA, but we hope it has more and more homebrew stuff like this.  

Thanks to Rogier PA1ZZ for sending me this. 

The Importance to Bell Labs of Lunch or Breakfast with Harry Nyquist -- "The Communicator" -- Bimonthly Publication of the Surrey (British Columbia) ARC.

This is a good sample (!) of the great content to be found in "The Communicator." This is the bimonthly publication of the Surrey (British Columbia) Amateur Radio Club.  You can find the publication and digital back issues here: https://ve7sar.blogspot.com/ 

There is a lot of great material in this publication. 

Pete N6QW Has Hybrid Rig On-The-Air

 

A thing of beauty on a wooden board.  Pete's post: 

https://n6qw.blogspot.com/2024/11/11252024-1st-dx-with-40m-hybrid-rig.html

"Them that know can make it go!"  Indeed.  

Pete talked about the history of this rig, and especially of the Thermatron portion of it, in the most recent episode of the SolderSmoke podcast: 

https://soldersmoke.blogspot.com/2024/11/soldersmoke-254-audi-and-video-versions.html

Thanks Pete! 

Oscar 7... and Oscar 11 (aka UoSat-2)? Did Oscar 11 do much the same thing as Oscar 7?

Above is a pretty good video by Retro Rockets.  Some will quibble about the technical details presented, especially about early radio, but I think the video does a pretty good job of describing the early production of ham radio satellites.  

As I watched this video however, I started to wonder if OSCAR 7 was in fact unique in coming back from the dead.  Back in 2018, I watched signals from OSCAR 11 (aka UoSat -2) as it tumbled through space with its battery dead, powered by a direct connection to its solar  panels: 

https://soldersmoke.blogspot.com/2018/12/ghost-ship-oscar-11-tumbles-through.html  

This was what Retro Rocket said was Oscar 7's claim to fame, right?  

In both cases, what happened was pretty cool, but did OSCAR 11 sort of repeat the supposedly miraculous rebirth of OSCAR 7?   

Sam WN5C uses ChatGPT as an Emergency Elmer

Sam WN5C has been on the blog before.  Last year we covered his heroic use of a Michigan Mighty Mite at Thunderbird State Park:  https://soldersmoke.blogspot.com/2023/06/sam-wn5c-builds-michigan-mighty-mite.html

This time, Sam writes about a good  ham radio use for ChatGPT: 

Hope you’re doing well. Just a quick note: ChatGPT is turning out to be a great homebrewing tool for me.

My elmer has been swamped with family issues, so my basic questions (“can you explain this circuit for me”) and hard questions (“why doesn’t this circuit I built work?!”) that he usually responds to right away has been a bit delayed. I’m in the process of designing a 5-band QRP CW transceiver with a superhet receiver and SSB receive so I’m learning a bunch of new circuits.

 

I’ve hated the idea of AI as someone who writes a lot (it cheapens what I’ve spent my career trying to perfect!), but man it is smart. I can ask it all kinds of questions. For example, it helped me design a little IF amp last night and ensured I got my impedance matching right (it’s great for mashing up lots of circuits and ensuring they work together). I can ask it for suggestions on part types and values. It helps with Arduino code if you’re into that. You can use plain language but it does well with heavy jargon. And, which I find really cool, it will step you through troubleshooting. It teaches the math, too.

 

Anyway, you or your readers might find this helpful. Especially when one is building at 3 AM and needs an answer immediately.

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

Thanks Sam! 

 

Tezukuri and Chappy Happy -- Amazing Videos on Homebrew Radio (from Japan?) - Another 40 Meter Direct Conversion Receiver

So around the time we were building 40 meter direct conversion receivers, someone else was doing something similar.  His product (above) is a lot nicer than ours.  He has an S-meter and a digital frequency readout.  But like ours, his is built on a wooden board.  FB OM.  

If you want to see what a direct conversion receiver can do, watch his video (above). 

I was really amazed to see him use a modified VFO from a Kenwood TS-820.  Not long ago Pete N6QW spotted one of these on e-bay and recommended that I buy it.  As with the Yaesu FT-101 VFOs, we bought it for the gears and reduction drives but ended up with the entire VFO circuit.  I now have one on my shelf, ready to go.  TRGHS. 

We are not sure who Chappy Happy is, but "Tezukuri" means "hand-made" in Japanese. The writing in the video descriptions are in Japanese, then Chinese. 

Here is the YouTube channel.  Amazing stuff here:  https://www.youtube.com/@chappyhappy3675  He is clearly a ham.  He even works on an old S-38.  Who is this guy?