
The Single Transistor Radio - jerryr
http://www.mindtribe.com/2014/06/the-single-transistor-radio/
======
linker3000
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".

I think this is where I put "Plus ça change..."

~~~
rdtsc
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.

~~~
crististm
"...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.

~~~
m4x
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

~~~
crististm
You make it sound so complicated. It is and it is not. They built FM radios
one hundred years ago...

------
pling
Nice. Some comments:

\- 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.

------
sdegutis
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.)

[1]: [http://atreus.technomancy.us/](http://atreus.technomancy.us/)

------
matthewmcg
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:

[http://en.wikipedia.org/wiki/Regenerative_circuit](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...](http://www.arrl.org/files/file/Technology/tis/info/pdf/0009061.pdf)

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:

[https://dl.dropboxusercontent.com/u/2541109/regen_tune.mp3](https://dl.dropboxusercontent.com/u/2541109/regen_tune.mp3)

~~~
matthewmcg
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.

------
bsder
Don't really understand the fuss, here.

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.

~~~
pling
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.

~~~
raverbashing
In practice, a transmitter like that doesn't go much further than 50meters,
there isn't enough power

~~~
kefka
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.

~~~
raverbashing
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)

------
jacquesm
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:

[https://www.google.com/search?client=ubuntu&channel=fs&q=sin...](https://www.google.com/search?client=ubuntu&channel=fs&q=single+transistor+radio&ie=utf-8&oe=utf-8)

Shows plenty of results, one of which is the article linked here.

~~~
pling
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.

~~~
jacquesm
straight from TFA:

"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.

~~~
pling
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.

------
geff82
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!

~~~
simmons
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. :)

