Radio Projects
First Posted March 8, 2008
Modified March 15, 2008

    I have been fascinated with building radios since I was 13 (and that was in 1966).  One of the funnest projects I had to do when I was a senior at UCSB was to build a super heterodyne radio.  Our goal then was to make the best radio we could.  And mine turned out very well.  But I remember back to the days when I was in Junior High and High school when I would build simple radios, generally involving one or two transistors.  And I also had fun building AM transmitters.  Several years ago I started getting the bug again.  My goal is to employ the experience I have had over the last 30 years to help me build some fascinating radios with a minimum of parts.

    The projects I have in mind are a simple TRF receiver using just two transistors, and also a simple superhet receiver that will be pretty much completely scratch built.  Right down to the IF transformers.  Although, that is not really so much by choice.  Getting IF transformers is not easy.  And it doesn't look all that hard to build my own.  And that will enhance the challenge of the project.

TRF Reflex Receiver


The above circuit...as of March 8, 2008, is very preliminary...and untested to say the least.  This is a double tuned circuit.  Both the input and output is tuned to increase selectivity, although, this will make it more difficult to align.  The two RF transformers are going to be custom built.  When the time comes, I will provide details on how to do that.  Of course...those who think they can build it, I say, go ahead.  There are a few things I am sure that will have to be tweaked.

Simple Reflex SuperHeterodyne


And this is a first cut at a two transistor superhet receiver.  This one is going to be interesting.  First off, all of the rf transformers are going to be built from scratch.  The last time I built a superhet receiver was when I was in college.  That one was a real doosie.  Here I am going for minimalist.

Very Simple Broadcast Band Transmitter


The above is a very basic transmitter circuit.  Now, this one I find interesting because this is the circuit that I used to make my first transmitter.  I got it out of a book I check out in high school.  It was always iffy if I could get this thing to work.  However, with better components, it is not quite so hard.  Although, there are still some things I don't understand about it despite the fact that I am an EE and should know better.  I was able, however, to even get it to work up around 27MHz on occasion back then.

Now, please be advised, I have not actually tested any of these circuits as of this time.  I don't have time :-(.

One thing I have noted over the years of building radios is that they oscillate.  You can never get an oscillator to oscillate.  But it is no problems getting a receiver to do so.  Radio receivers must have a lot of gain in order to receive the weak signals that are propagating through the ether.  When you combine this with all the coils and rf transformers, well, you have a recipe for disaster.  All I can say is good grounding techniques, careful wiring, and shielding are your friends.

I hope to do so real soon.  And I hope to have some real fun projects that other may find amusing and educational.  I have a very soft spot in my heart for radio circuits, because this is where the hobby started for me.


Winding Coils
First Posted March 15, 2008

Winding coils has never been one of my favorite things to do.  They almost always turn out looking very crude.  But then I remembered I have some pretty good tools.  I used a piece of 2 inch PVC to make the coil form you see below.  I cut off a piece about 8 inches long so that I could chuck it in my lathe.  #22 wire can be wrapped at about 33 turns per inch.  The closest thread I can cut with my lathe is 32 threads per inch, so that is what I set it to.  I made two passes so that I could make fairly light cuts to keep the plastic from melting.  Then using a cut off tool, I trimmed off what I needed.

I then used a #60 drill to make the holes that the wires go through.



Then I got out my spool of wire and began winding the coil.  With the thread pattern cut in the form, winding was a lot easier.  It wasn't too much problem keeping it looking fairly neat.  Although, it was the little tickler coil that was the hardest to wind, for some reason.  I wasn't able to keep a hold of the wire and had to start over twice.  The big coil I got the very first try.



I intend on using this coil in an RF generator.

Until next time.