The Single Transistor Radio
mindtribe.com
mindtribe.com
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..."
Also, the receiver and transmitter are awfully similar (in practice, if you build a receiver it will interfere with "everything" around it)
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?
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.
As in - two seconds is three orders of magnitude larger than it should be.
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.
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
- 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.
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.)
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:
http://en.wikipedia.org/wiki/Regenerative_circuit
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.
The ARRL published an easy-to-build transistorized version a while back: http://www.arrl.org/files/file/Technology/tis/info/pdf/00090...
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:
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.
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.
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)
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:
https://www.google.com/search?client=ubuntu&channel=fs&q=sin...
Shows plenty of results, one of which is the article linked here.
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.
Seeing as it's 49MHz, it'll even show up on analogue baby monitors etc.
20 m? It used the mattress base as antenna.