If you time-warped back to sometime around the 1970-80s and showed this article to a bunch of electronically-minded people, ignoring the SDR stuff, they'd take a quick look and say something like 'um - yeah' and move on.
This type of one transistor radio is/was a really common circuit and probably the vast majority of hobbyists built something similar - all without having to run a simulation first. I can recall spending a happy afternoon as a boy in that time period sorting through my box of stuff, pulling out a DL96 vacuum tube and knocking up a MW/SW receiver. I also left countless 'cats whisker'/crystal set (germanium diode) receivers and ZN414-based creations in my wake.
The one thing I get out of that article is that technology has moved so far that we now get impressed by the simple stuff - the fundamentals - it's becoming a lost art.
I'm not sure I've picked the best modern analogy - but perhaps think of showing someone a USB flash stick and saying "...and when you plug it in to your PC YOU CAN SAVE FILES ON IT".
The key is "electronically-minded people" phrase I think. Back in the 70s-80s it meant "analog electronic minded people" so these things didn't impress them because there weren't many ways to become electronically minded back then without playing with analog electronics at some point.
Today, well... electronically minding could be programming, hardware, that could be digital of course not just analog. These seemingly basic things are just pushed behind a lot of layers of abstractions. It could be building drones, remote control sensors, machine learning, writing games, building distributed systems.
Another way to think about is when you have 1Gbps link to your house and 4GHz consumer CPUs not many people will think about analog circuits. They are just too far down in the stack. So when someone mentions those things they seem rather fascinating.
I say these things because they kind of mirror my experience. I used to take apart electronics, build radios, remote controlled toys. But, then I got computer. Started to get interested in programming. My box of analog components is still at my parents' house. I have a soldering iron but haven't touched it in 10 years now.
"...4GHz consumer CPUs not many people will think about analog circuits..."
That may be true but the same people don't think about digital circuits either. And interfaces with the real world are and remain analog. They are not digital.
Analog circuits such as you would find in a radio are quite different from the analog IO used when interfacing with the real world. Reading an analog signal from a sensor and acting upon it is trivially simple when compared to building an FM modulator that relies on feedback loops, phase offsets, non-linear junctions and so on.
I think there are a lot of people in the world right now who are interested in electronics, and have become fairly good at using digital electronics but still view analog as mysterious and magical. In that case an article like the above will be very interesting to them
I was the same until I got into embedded stuff. Started up writing a LP filter in software for something that was buggy as hell and slow and the tooling kept falling over. Changed the design for a simple RC+op amp LP and fell in love with analogue again.
Yes mine does this as well. Totally agree. They went to some insane design effort however for it to remember where it was in the mp3 stream though when you disconnect it for a few seconds to turn the ignition.
It isn't that the fundamentals themselves become impressive. Rather, we have so much complexity these days, we forget what can be achieved with only a little.
I listen to music & radio on my laptop & cell phone, both of which have billions of transistors and thousands of discrete components, compared to the 9? 10? in this circuit.
In a sense you could look at this sort of thing as an implied question along the lines of, for all the orders and orders of magnitude of complexity we have now, what has it bought us?
Reminds me of learning to code on an early IBM-PC. I coded because I wanted it to do something different. Now 'different' is learning how to install a bazillion libraries and dependencies and hoping I can change that one config file just right to get it to do what I want.
It goes back farther than that: For ham operators, there was a single-tube radio published in 1932 that pretty well laid out the principles.
http://www.w7ekb.com/glowbugs/tx/hartleyonetube.htm has a nice summary.
Agreed. I restricted my time warp to a period where transistors/FETs were ubiquitous and finally cheap for the hobbyist, but as you say the principles go way back.
True story: at the coffee shop just this week, I overheard a conversation of someone explaining exactly that. The person they were talking with didn't know how to transfer files between two computers, and was absolutely amazed at the idea of a flash drive.
- he used simulation up front. This is a great thing. Some more detail would have been nice. I tend to design small circuit components up front on paper with a good old fashioned calculator then simulate in LtSpice. It kills a lot of frustration and things you've forgotten about. However it doesn't always work out as SPICE can't deal with parasitic inductance and capacitance easily without adding primitives to the net. This kills you after a few MHz.
- The art of electronics is a terrible book IMHO if you want to learn electronics. Even as a reference its not great. It's disjoint and poorly written. Better bet is the ARRL handbook even if you don't do RF stuff. The material is wonderful in that book. Being American though, it is undergoing a transition to SI units though so its a little inconsistent in the maths with random multipliers here and there.
- nice to see something without a microcontroller in it and some manual work (coil winding).
I still wish all electronics was at this level. Much more fun.
I've been getting into electronics lately and really loving it! My inspiration was my new Atreus keyboard[1] (first one ever sold!) and the epiphany while playing Minecraft that making your own (useful) stuff is tons of fun and super rewarding. And it doesn't have to be computer programming anymore!
So I booked it to Radio Shack and bought the Make: Electronics book and the accompanying kit. (I could have scoured for the individual parts, this book lists them and recommends it, but it was a nice convenience to have a pre-made kit by the same company, and presumably the same author.) And so far I've only learned about resistors, capacitors, and other basic circuitry, and it's a bit math-heavy, but it's really exciting!
I also have a serious electronics project in mind that acts as really good useful motivation. It's a toy that's probably relevant to HN, and if I ever accomplish it, I plan to share it here.
Hobbyist electronics is really fun, and so far I recommend it! (That said, I have no ambitions about inventing the next great CPU or memory chip -- you probably need decades of college-level education and experience on this to be able to innovate at any serious level these days.)
This is nice. Even with all of the other objectively more impressive technology we use on a daily basis, simple radio circuits still seem like magic to me.
If you would like to play with a "one transistor" receiver, check out the Armstrong regenerative receiver. This circuit uses a single gain element as tuned oscillator/RF amplifier. The output is inductively coupled back in to the circuit for re-amplification. Since the circuit is tuned, this increases selectivity as well as gain. See:
Edwin Armstrong invented this when he was in college and vacuum tubes were quite expensive. One gain element handles oscillation, amplification, and demodulation for obvious economy. Despite this, performance is quite good.
This circuit is much harder to tune than it is to build. Once you master the steady hand action required (and learn not to move once you find a signal), you can easily pull in overseas shortwave broadcasts with a wire antenna.
Here's a short audio clip of me tuning my version of the ARRL regen receiver across a shortwave broadcast band:
Bonus: 20s into the clip (recorded early July last year), you can hear Radio Nacional Venezuela complaining (in English) about the diversion of Evo Morales' plane.
Better articles can be had from old issues of Popular Electronics, and you'll actually be able to listen to it on your radio at the actual 90-100MHz bands.
You can listen to that on baby monitors. Also broadcasting on "broadcast FM bands" is frowned upon world-wide. The 49MHz band is for experimentation as assigned by the FCC in the US.
Sigh. Spoken like someone who hasn't troubleshooted badly acting radio hardware/software.
1. Depending on antenna, can go very long distances. I've seen crap omni's used for QRP work, and still go hundreds of miles. This very much depends on frequency, ground-wave propagation, current ionosphere status, and solar activity.
2. There are limitations on harmonics. And in the said circuit, it is a great reference circuit. However, harmonics will bleed into other bands. Not Good.
1. Sure, what I meant was "for this type of transmitter in an amateur setting and frequency range ~ 100MHz", where the antenna is usually a wire poking out and the transmitter is inside of a building
If you're doing QRP work with a professional antenna and a different frequency band (and good receptors), you're right, it can go very far
2. Yes, harmonics are an important issue. I'm not sure how they would behave in a "bad quality" circuit like this (even though "bad quality" usually mean more harmonics, the fact that you have a general purpose transistor, component leads, traces, etc, all contribute to prevent them from being amplified too much in the first place, if you're at 50MHz you'll surely have 2nd, 3rd, but probably not much beyond that)
Except that it isn't actually a radio but an oscillator that you could use to build a radio (by mixing the output of the oscillator with some input signal that you want to demodulate, and then to use the LF output of the mixer, aka the difference frequency).
But the article doesn't do that, and then goes off to show how you can turn this oscillator into a primitive (unmodulated, so only a carrier wave) transmitter.
(fun thing to do: wind that coil from thinner wire and demonstrate the microphony effect by talking to the coil, or glueing a plastic toothpick to it and a membrane to make it more sensitive).
If you really want to build a single transistor radio:
It is a radio and has FM modulation. Doesn't need complicated mixing for FM if you can skew the osc resonant frequency quickly I.e you don't need an IF system. In this case the transducer does that.
Its not CW, as that is switching the osc on and off.
This is as basic as it gets however. Noisy, full of harmonics but nevertheless cool. I've seen stuff not much more complicated than this doing some impressive distance.
"So now you should in theory have a working FM transmitter. How do you test it? Well you could build an FM receiver, which would almost be identical, just in reverse. However, I believe this would be an excellent opportunity to demonstrate the utility of SDR. With a $20 USB dongle from Amazon and the following tutorial, you can operate your own SDR receiver from your computer."
So no, it's not a radio. The radio is in the dongle, the other part is just an oscillator. So it's more likely about 1/2 million transistor radio or thereabouts (estimate of the # of transistors on the chips in that dongle).
The 'crude mixer / demodulator' can be done with just one transistor, this just isn't that.
It is a radio transmitter (and therefore a radio) regardless of what the TFA says. If you drag our your field strength meter or scanner and tune it to around that band, you're going to get a signal. Probably not a very strong one but it's still there. The big chunk of wire hanging off it is clearly an aerial so it even shows intent of being a radio.
Seeing as it's 49MHz, it'll even show up on analogue baby monitors etc.
This isn't the simplest radio (or oscillator) you can build. To get the nearest AM-station, simply put a resistor, an a diode together and attach 20 m of wire and an earphone on its side. Voila!
When I was a kid in the 80's, my parents once grounded me from my computers and radio. I wired a diode and earphone to the TV antenna lead in my room, and could listen to the town's radio station again. No resistor and completely the wrong sort of antenna, but I guess radio can be very forgiving when there's a single strong nearby signal. Good times. :)
I remember a TV program, in Spain in the 70's. They explained how to do one AM radio with one transistor, an AA battery, half a metre of copper wire and an earphone. Worked fine.
This type of one transistor radio is/was a really common circuit and probably the vast majority of hobbyists built something similar - all without having to run a simulation first. I can recall spending a happy afternoon as a boy in that time period sorting through my box of stuff, pulling out a DL96 vacuum tube and knocking up a MW/SW receiver. I also left countless 'cats whisker'/crystal set (germanium diode) receivers and ZN414-based creations in my wake.
The one thing I get out of that article is that technology has moved so far that we now get impressed by the simple stuff - the fundamentals - it's becoming a lost art.
I'm not sure I've picked the best modern analogy - but perhaps think of showing someone a USB flash stick and saying "...and when you plug it in to your PC YOU CAN SAVE FILES ON IT".
I think this is where I put "Plus ça change..."