SolderSmoke Challenge – Bonus Episode – Using your oscilloscope to test your DCR
New homebrew radio builders often struggle with test and measurement. You can build a board perfectly but if you don’t have your tools setup correctly you won’t be able to tell if your board is working, or worse you’ll thing it is not working when it is working perfectly. In this bonus episode Dean, KK4DAS takes us through the basics of configuring and oscilloscope to test the boards, particularly the PTO oscillator, buffer, and the mixer.
We say this often, but if you really want to learn about oscilloscopes and test and measurement there is no better resource than our friend Alan, W2AEW’s YouTube Channel. Check it out!
Alan Wolke, W2AEW’s YouTube Channel:
https://youtube.com/@w2aew?si=
Join the discussion - SolderSmoke Discord Server:
Documentation on Hackaday:
https://hackaday.io/project/
SolderSmoke YouTube channel:
https://www.youtube.com/@
SolderSmoke blog DCR posts:
SolderSmoke Challenge – Direct Conversion Receiver – the Audio Amplifier Build and Receiver Demonstration
In this episode Dean, KK4DAS wraps up the initial build of the SolderSmoke Challenge DCR. He takes us through the audio amplifier stage and demonstrates the newly built receiver just moments after connecting the audio module to the mixer and hooking up a speaker. The audio module is conceptually simple – three nearly identical stock-standard common emitter audio amplifiers which provide the 80-100 dB of amplification you need to go from microvolts of RF to volts of audio to drive a speaker. The challenge with all that amplification in a small board is to keep it amplifying but to stop it from oscillating and as you’ll see in the video, good construction technique is critical to good performance.
And wow! We now have more than 30 builders working on the SolderSmoke Challenge, with more builders completing the challenge every day. And those are just the ones who are active on tour Discord server. If you have completed the DCR or even if you have just started building it, we want to hear from you. Send a picture or better yet a video – make it a selfie and you can join the SolderSmoke challenge hall of fame!
And if you are not yet building it, you must ask yourself one question:
What are you waiting for?
Join the discussion - SolderSmoke Discord Server:
Documentation on Hackaday:
https://hackaday.io/project/
SolderSmoke YouTube channel:
https://www.youtube.com/@
SolderSmoke blog DCR posts:
https://soldersmoke.blogspot.
Dean will soon post his longer video on how to build the fourth and final board of the SolderSmoke Direct Conversion Challenge receiver, but we know many builders are chomping at the bit, and are going ahead with the building of the AF amp board. We hope that this short preliminary video will help. Here Dean descibes the benefit of building the three stage amp, ONE STAGE AT A TIME.
Response to the challenge has been great. There are at least 30 receivers under construction around the world. Many are already inhaling RF. All of the problems that arise with true homebrew are being identified and fixed. Dean's full AF amp video will be out shortly. Thanks Dean!The SolderSmoke DCR challenge is going well. Our Discord server is bustling with activity and we are impressed that several intrepid homebrewers have already completed the receiver. So, we know that you can too! In this episode Dean, KK4DAS walks us through the design and construction of third of our four boards, the 40-meter band pass filter. The band pass filter ensures that the only signals that get through the receiver to the speaker are those that are in the 40-meter band. Dean also gives an update on the Challenge and discusses some recent improvements we've made to the circuits based on feedback from our builders.
Join the discussion - SolderSmoke Discord Server:
Documentation on Hackaday:
https://hackaday.io/project/
SolderSmoke YouTube channel:
https://www.youtube.com/@
SolderSmoke blog DCR posts:
The response to the SolderSmoke DCR challenge has been terrific -with nearly 7,000 views of the first episode! Thanks so much for checking it out. The goal is to convince you that you can build your own receiver and then go get you started on Homebrew ham radio. We already have confirmation that it can be done! Congratulations to Peter, VK3PTM and Matthew, KY4EOD who have both completed the receiver. The boards look good and, even better, they sound great. Videos and descriptions are here on the blog and on the SolderSmoke Discord sever. Speaking of the Discord server, we already have a very robust conversation going, It’s a great place to give feedback and to get your questions answered. Builders are helping builders and we at SolderSmoke are trying to answer as many of your questions as we can. This is a beginner’s project, so all are welcome.
In episode 2 of the SolderSmoke Direct Conversion Receiver challenge we tackle the PTO. We discuss a bit of the theory, walk through the schematic, and take you step-by-step through building and testing the oscillator and buffert. By the time we are done we will have achieved JOO! (the Joy of Oscillation). And when you build it you will be 1/4th of the way to having build your own 40 meter receiver.
Links:
Join the discussion - SolderSmoke Discord Server
Documentation on Hackaday
https://hackaday.io/project/
SolderSmoke YouTube channel
https://www.youtube.com/@
SolderSmoke blog
This is the first in a series of videos and postings on the SolderSmoke Direct Conversion Receiver challenge. Dean, KK4DAS takes us through an overview of the project. He covers the architecture of the receiver, construction techniques, component sourcing and selection and generally sets the stage for the build. Future videos will cover each board in detail.
We are very excited invite you to join the SolderSmoke Discord server. This is an experiment to see if Discord is a good forum for SolderSmoke listeners to interact with us and each other on topics of interest. For now, we will be used Discord exclusively for discussion of the DCR challenge. To join the SolderSmoke Discord server click on the link below.
Links and references:
• Join the discussion - SolderSmoke Discord Server
• Documentation on Hackaday
• High Schoolers Build a Radio Receiver | Hackaday.io
• SolderSmoke YouTube channel
• SolderSmoke -- Homebrew Ham Radio - YouTube
• SolderSmoke blog
• https://soldersmoke.blogspot.
Derek wrote:
Bill,
It is a thing of beauty. You can see all four stages in there. There is the Bandpass Filter in the upper left. Below that is the VFO. In the center you can see the SBL-1 mixer. Off to the right is the audio amplifier. FB Chuck!
Chuck KE5HPY writes:
Allow me to add an endorsement of the joy and practicality of the DC receiver. Whether XTO, VFO or DDS, ring diode mixer, or Polykov, the DC IF concept is a real winner. They really deliver wonderful audio and clarity that is very satisfying for homebrew builder.
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:
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.
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.
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.
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
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?
Geoff N6GWB and his eldest have produced a really wonderful receiver, and have joined the elite ranks of those who have built their own receivers. Congratulations to both! ( Be sure to watch the video below.)
Geoff writes:
Though I built it, my eldest has retained naming rights. Behold the Rad Radio Receiver, an Soldersmoke inspired build. It’s a 40m DC reciever. I had planned on making this a truly 50-50 N6QW N2CQR build, but I needed to get it done for a show and tell this Wednesday. I have N6QW dual JFET RF amp and mixer modules. I have the N2CQR ceramic ocillator circuit from the 2017 DC receiver project. I had planned on including the all analog audio amp from the more recent N2CQR DC project, but alas, time got the best of me. I was hoping to make the whole thing all-analog. (I thought the all analog would get me more “hard work” kudos at the show and tell.) I ended up including a LM386 audio amp making this a bit of a cyborg.
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