Radio receivers part 1: from scratch

This will be a collection of simple instructions on building an actual radio or two with household items.  It will further demonstrate building one's own capacitor(s), and detector diode...again, from household items.

Some care will need to be taken when soldering and when working with items like razor blades, etc.  but the careful person should have no difficulty in constructing these using the plans I will outline.

Step 1:

We will build a few simple radios with this first in the series of Radio instructables.

The very first one, having only 2 parts to it.

Warning! This radio MAY NOT WORK in your area if there are no close by, strong stations.  If you have a really close AM station, you may be able to get this to work.  It is so simple though, that it is worth a shot.

First, find yourself a "piezoelectric" type earphone (not the magnetic and plate kind, they will not have the sensitivity needed).

Strip off the insulation (if there is a plug, it will need to be removed) from both wires.

Now, find yourself a 1N34A Germanium diode (low forward voltage, high sensitivity).   solder the one wire of the earphone to the diode as in the schematic. 

Now, tape (duct tape is good here) the other end of the diode to a water pipe (the facet at the sink is good), and grab the remaining free wire in your hand.  You have now become the antenna, and the faucet the ground.

IF you hear anything at all, it should be a faint AM station. 

There are 2 problems with this radio,  actually at least 4 problems:

#1: it is not tunable, you can't "pick" the station you wish to listen to,
#2: it is not loud, IF you hear anything at all,
#3: it is not portable at all
#4: IF  you have more then one station nearby, you will hear all of the strongest ones.

Comments

[i couldnt think of a name]

oh ok thanks

[i couldnt think of a name]

does it matter what size of wire i use on this?

[Goodhart]

Only when it comes to to coil and the antenna. With the coil, you'll not want to ues very heavy wire (coated, so called Magnet wire is suffciant for the coil). The antenna depends on the length. IF you do not use a standard antenna as I tried here, a long 40 foot piece of magnet wire. does well (if you have the room for it).

[electronicz]

Where does the 936 feet in the equation come from?

[Goodhart]

Here is a better description of the reason than I could ever give.

[electronicz]

Ok, thanks

[nutsandbolts_64]

No close stations you say? Maybe I can modify the coil and tune it to airport frequencies (assuming I can actually get one to work with FM, if I can...)

[Goodhart]

The plans here, and the ones I will soon add to this (by means of a link) are pretty low frequency (and FM is in a bit of a higher range). The use of a "crystal diode" which will be illustrated in the next ible, will help tune in a station, but you probably will not be able to get anything on "the FM dial", without a lot of modulation.

I have, inadvertently picked up AM stations on many devices though, not meant to receive such a signal, from digital recorders to home made buglar alarm systems....sometimes it is comical, but mostly it is just annoying :-)

[nutsandbolts_64]

Speaking of tuning, can't a sliding mechanism slide a screw back and forth then tighten it to make contact with the coil. It would have a small, thin conductive object (a needle?) that would handle precision. My friend made one a few weeks ago and both of us had no idea what may have caused the difference in signal in the ff. situation:

My friend set-up the radio inside his house, and he got random signals from some random station which I can clearly hear when he stuck the earpiece up to the microphone on the telephone. He then set it up outside the house, but he surprisingly received weaker signals. I hypothesized the surrounding buildings may have somehow affected the signal, but we wouldn't know unless we demolished the entire block.

[Goodhart]

On one of the earliest "crystal" sets I ever build (decades ago) the coil was not tapped as mine is here, but rather a piece of metal was bolted to the wood base, using two washers, so it could be moved back and forth, and bent an angle up closer to the coil, so only a "cut out point" would touch the coil. Of course, this meant running the metal piece back and forth over the chemically coated wires until they were worn through and contact could be made but that was a very simple method for making a nearly infinite amount of variability.

[nutsandbolts_64]

Not exactly what I meant... But it appears I went a bit off course from what you meant. In whichever case, has anyone considered using aluminum wire? Galvanized wire perhaps? Any metal that doesn't need a chemical coating in order to reduce its corrosion. Although yes galvanized wire is coated, what it's coated with is still electrically conductive. I don't know how this would affect resonance, but it's worth a shot -- wow I just got an idea. Interchangeable coils anyone? I did instantly realize the pros and cons.

Pros:
-No need to fine tune into desired radio station

Cons:
-Carrying a box full of coils isn't really viable for portable sets, unless you really want to

Thoughts?

[Goodhart]

The coil would have to be wound VERY carefully if not coated, so that NONE of the wires TOUCHED each other. That would constitute a short, and the coil wouldn't be a coil anymore.


I have a box of coils, most of them are not really as useful as one might think.  Since we are looking at the need for such a BIG coil, carrying a bunch of those around would be cumbersome (at very least ;-)  

[nutsandbolts_64]

Now I realized how off course I really am... How about you remove the coating on one side, and physically separate the exposed surfaces with some sort of dielectric? And here we are exploring all the options on how to reinvent the coil (reinventing the wheel is a bit too far-fetched).

[Goodhart]

Sounds painfully hard to do, to be honest. Using the coated wire, one only need run the blade of the adjuster bar (more like a then bent piece of metal) a few times to wear through a ridge for contact. My "tapping out the coil" method actually complicates the original crystal set I had, and maybe unnecessarily so.

[nutsandbolts_64]

Agreed... Maybe then there is no need to reinvent the wheel (ahem, coil). Then it looks like the tried and true methods are the best techniques for use on crystal sets. It all comes down on experience, and that's where most people are lacking (of which also includes me).

[Goodhart]

Yeah, I was kind of thrown into it head first as a youngin, some 38 - 39 years ago or so.....was cool then to "listen to a radio without any electricity" :-)

[nutsandbolts_64]

Speaking of the radio, would magnet wire from a burnt-out coil from an electric buzzer suffice? (the electric buzzer is from a door bell)

[Goodhart]

as long is "burnt out" doesn't mean the insulation was "burnt off" (a continuaty meter clipped on both one end and drawn along the length of the insulation, should tell you).

[Infinitevortex]

Nice. Looking forward to the next episodes!

[Goodhart]

I am having difficulties finding the time....hopefully this weekend.

[DELETED_explosionist]

(removed by author or community request)

[Goodhart]

In my next installment, I will be demonstrating how to make one's own capacitor, diode, and coil.

[DELETED_explosionist]

(removed by author or community request)

[Goodhart]

It isn't anything fancy, just the "very" basics from days gone by :-)

[Cybot Rules]

Niiccee Work (:

[Goodhart]

Thank you :-)
This is just the beginning of a couple (2 or 3 at least) in series that I will post links to one another inside the ibles,  so anyone can find the others quickly, once they are finished.

[Goodhart]

Sorry ! I had forgotten to upload the schematic....fixed now.