First, you probably need to turn on closed captioning, and select autotranslate, probably to English. This video is worth it.
This fellow takes on the self-imposed challenge of homebrewing a 2 meter FM receiver. He builds it on a copper clad board, using what looks like dead-bug construction techniques.
He is not a radio amateur. But he should be one, just by virtue if his work on this receiver.
The board looks a lot like one of our projects. He even points out the large number of parts that have been removed from the board. You get the sense that he shares in our common frustration with circuits that for some unknown reason just won't work. I found myself worried that he might opt to remove ALL the parts from the board -- that is our homebrew nightmare.
Fortunately, he does not reach this extreme. He gets the thing to work. It is still not perfect. He will go back to it later. Good idea. Take break. Walk the dog or something. Insight will come.
It is really great and refreshing to have this kind of "warts and all" "blow by blow" description of a build projects. Too often the books present projects as if they worked the first time the builder put them together. This happens very infrequently -- the process described in this video is closer to the norm.
And it is great to have this project come to us from Germany. SolderSmoke is dedicated to INTERNATIONAL homebrew radio.
First, it is a good day when I find a new Chappy Happy project on YouTube. Thank you Chappy Happy! You make us happy!
Second, even before I watched the full video, I could recognize the PAL VFO. This is an old CB device. You will find them at hamfests. I picked one up several years ago, knowing that I will someday use it as a VFO or for VFO parts. It is, after all, an LC VFO, and it is to be celebrated and used.
Chappy Happy turns his PAL VFO into a simple direct conversion receiver for the 25 meter SW broadcast band. He is on the west coast of North America and uses it to listen to Radio Japan. He uses a J310 RF amp and an NE602 Gilbert Cell mixer.
That is great, but there is a big problem in using a direct conversion receiver to inhale AM signals: Unless you can get the frequency AND the phase of the VFO to be exactly the same as the carrier, you will have distortion. You will not have this problem if the signal is SSB, but you will have it with AM or DSB.
I think I can hear the distortion on the Radio Japan signal. Can you hear the flutter? That is what happens with an AM signal being received on a DC receiver. This is why Doug DeMaw frequently warned that you could not listen to a DSB signal on a DC receiver without significant distortion.
What do you guys think? Can you hear the distortion? Should Chappy Happy turn this receiver into a simple superhet, perhaps something like the Q-31?
Here is a video of my Q-31 super het for the 31 meter SW band:
Again, thanks Chappy Happy! Please keep those projects coming!
Wow, this is very cool. I don't have a 5 inch naval gun mount. And NASA has never called me for any reason. This is all almost too much. Watching it all, I feel an urge to go UHF.
This interview was a lot of fun. I too was smitten at an early age by the HW-101. I still have one on my operating table. We are all lucky that Will is working in an innovative way on these old rigs. Who can forget his shocking water and soap (followed by South Texas sunshine) approach to cleaning these often cruddy old rigs? Thanks Will and thanks Eric for doing this interview.
I admit to being biased in favor of any project from Norway. This is the result of the fantastic videos of Helge LA6NCA. But even without the influence of Helge, this workshop/workbench project would stand out. It is really good. It is filled with good ideas. I like the way he makes use of 3D printed parts. The lighting scheme is excellent. I like the chair he got. There is a lot of humor in this video.
But you may have done things a bit differently -- please comment on what you would have done.
Thanks to Frengen Engineering. Here is the YouTube channel:
My posting of this video should clearly demonstrate the I am not a Ludite (one d), and that I am not opposed to technological change. I mean, look, Will has a Pick-and-Place machine. He has 3D printers. He has microscopes. I will likely never have these things in my shacks. But he has them, and uses them, and does a great job of explaining them.
I was also attracted to the video by the 12'x8' size of this shop. This rougly matches the sizes of both my Virginia and my Dominican Republic shacks.
I really liked the way Will built this shack. Many good ideas are in there. I especially liked his choice of flooring, and his ceiling mounting of video camera and microphone.
Like I said, lots of good ideas here. What did you find useful in the video? Please comment below.
A good friend, who was thinking very positively, sent me this video. I looked at it, and concluded that while this fellow seems to believe that he created this device, he really didn't. I realize that there are different views on this.
What do you think? Please put your comments below.
This popped up on Hack-A-Day yesterday and we were talking about it at the Vienna Wireless Society lunch.
Even if you find the topic to be, well, a bit off-topic, the presentation is entertaining and, I think, interesting. I have covered Wilson Cloud Chambers. And I have some experience (!) with Alpha particles.
Try not to eat it. And don't eat too many bananas!
Hidehiko reports that in Japan, this is called a "Self Quenching Circuit" and that it is popular with beginners. He notes that the quenching frequency is set by the values of the 5 Meg Resistor, the 50pF cap, the 33 uH inductor and and the 5.6k resistor. Its strength is adjusted by 10k variable resistor.
Note the two DC-DC convertors
A closer look at the coils.
We had some interesting back and forth with AI Gemini on this circuit. I wondered if a circuit this simple could in fact be SUPER regenerative. Might it be just a plain old regenerative receiver? AI Gemini looked at the schematic and confirmed my suspicion. TWICE!! This is a reminder that the AI can often be wrong. Emphatically wrong!
I asked earlier if this circuit could be a super regenerative circuit. You emphatically said that it could not be super-regenerative. But please reconsider. Look at that 33uH component. Could this be part of a self-quenching super-regenerative receiver?You are completely correct to push back on my previous
assessment, and I appreciate you prompting me to take a closer look. I was
wrong to emphatically dismiss it.
Looking at the provided "Circuit Diagram.jpg",
this circuit absolutely has the classic hallmarks of a self-quenching
super-regenerative receiver, particularly one designed for the VHF band.
Here is a breakdown of why this is the case and how the
specific components you mentioned factor into it:
The 33µH Component (TV Peaking Coil)
The 33µH coil acts as a Radio Frequency Choke (RFC).
Given the tiny values in the tuned circuit (a 0.24µH tank coil and 28pF tuning
capacitors), this receiver is clearly designed for VHF frequencies (likely the
FM broadcast or aviation bands, around 100 MHz).
At those high frequencies, a 33µH inductor presents a very
high impedance. Its job is to block the VHF RF energy from leaking down into
the audio output (AF OUT) and the power supply, forcing the RF to stay in the
detector circuit. Meanwhile, it easily allows the much lower frequency audio
signals—and the supersonic quench frequency—to pass through.
The "Smoking Gun": The Grid Leak Network
While the 33µH choke is necessary, the real proof that this
is a self-quenching super-regenerative circuit lies at the grid of the 6AK5
tube (pin 1):
The
5MΩ Resistor and 50pF Capacitor: This parallel RC network is the heart
of the self-quenching action.
In a
standard regenerative receiver, you want smooth, continuous oscillation,
so you use a much lower grid resistor (often under 1MΩ).
A 5MΩ
resistor is massive. When the tube begins to oscillate, it draws grid
current, which rapidly charges the 50pF capacitor with a negative voltage.
Because the 5MΩ resistor is so large, this negative charge cannot bleed
off quickly enough.
The
grid becomes so negatively biased that it completely cuts off the tube,
stopping the oscillation (the "quench"). The capacitor then
slowly discharges through the 5MΩ resistor until the tube can conduct
again, and the violent oscillation cycle restarts.
The "Regen ADJ" Control
You might have noticed the Regen ADJ 10k potentiometer at
the bottom. While standard regenerative receivers use these to carefully ride
the edge of oscillation, self-quenching super-regenerative receivers also use
them. In this circuit, adjusting the plate/screen voltage controls the aggressiveness
of the oscillation and fine-tunes the quench frequency for the best sensitivity
and audio recovery.
You made an excellent observation. The combination of the
VHF tank circuit, the RF choke isolating the audio line, and specifically that
ultra-high-value grid leak resistor confirms that this is indeed a
self-quenching super-regenerative detector.
