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CRYSTAL
SETS
4
A
Crystal Set By
Kenneth Rankin |
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| CRYSTAL SETS 4: A
CRYSTAL SET BUILT
BY KENNETH RANKIN |
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| MDS975.co.uk reader Roddie Rankin
kindly
sent in the details of a crystal set built by his son Kenneth for a
school project which won him great praise and merit. The
crystal
set is so nicely made and the project so well written that I thought it
deserved a special page of its own. |
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 Photograph Of Kenneth Rankin's Rather Super Crystal Set |
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| CONTENTS 1 - What Is A Crystal set? 2 - How A Crystal Set Works 3 - History Of Crystal Sets 4 - How I Built My Crystal Set 5 - The Results I Obtained 6 - Where I Found The Information 7 - Quiz |
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| 1 - WHAT
IS A
CRYSTAL SET? Perhaps
you
think, like I
did, that a crystal set is just a collection of lovely stones. In fact
a
crystal set is a very early, simple domestic radio. The photograph
above
shows the crystal set I built.
The crystal set does not have a battery. It runs completely from the radio waves it picks up in the air. It is absolutely free to run! Please read on to find out more about this exciting invention! |
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| The birth of
domestic
radio: A deluxe crystal set produced by Marconi for the
reception
of programmes from the first of the BBC's radio stations, 2LO in London. [from Pageant Of The Century - Odhams Press] |
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| 2 - HOW
A CRYSTAL
SET WORKS The diagram below
shows the circuit
diagram of the crystal set I have built. It consists of a
coil (L1), a tuning
capacitor
(C2), a diode (X1), an aerial, a crystal earpiece and an earth.
(Capacitors C1 and C3 are not essential.)
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Circuit
Diagram
Of
The Crystal Set
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First the aerial
picks up radio
waves from
radio stations all over the world. Then the required station needs to
be
selected, this is called tuning, and this is achieved with a Tuned
Circuit. The Tuned Circuit in the crystal set consists of two
items; a component called a variable capacitor and a coil of
wire.
By adjusting the value of the capacitor and coil tuning is achieved. The coil taking unwanted signals of low frequency straight through to the earth, which gets rid of them, while the capacitor takes unwanted signals of high frequency straight through to the earth. The remaining signal, in between the high frequency and low frequency signals, is the signal of the required station which is not passed to earth by either the coil or the capacitor. This is the frequency to which the set is now tuned in. You normally change the frequency to which a set is tuned in to by turning the knob on the tuning capacitor, thus receiving different stations by varying the capacitance of the variable capacitor. The number of turns on the coil can also be changed [called varying the inductance of the coil] and this will give different tuning ranges. A larger number of turns provided longer wavelengths [lower frequencies], while a smaller number of turns of wire provides shorter wavelengths [higher frequencies]. [ It is also worth noting that the inductance of a coil can be increased by inserting a component called a Ferrite Rod into the centre of the coil. ] Once tuned into the
required station
this
remaining signal goes to earth by travelling through the diode and
earpiece. The diode takes the sound signal out of the radio signal
[called demodulation], and passes it to the earpiece. The sound signal
travels through the crystal in the earpiece which vibrates the air in
the earpiece giving us the sound of the radio station to which you are
tuned.
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3 - THE HISTORY OF THE CRYSTAL SET The history of
crystal sets begins
with the first broadcast stations being opened. This happened in
England
in 1922. The simplest form of receiver for these broadcasts was the
crystal set.
In those early sets
they had "cat’s
whiskers"
instead of diodes. A cat’s whisker was a fine piece of wire
which was
adjusted to make a suitable contact with a crystal. The crystal would
be
made of a substance such as coke or galena. An example from
1923
is shown in the picture below. Notice how well made these
instruments were.
There
were several limitations to
the crystal set: it needed a big aerial, an earth connection, the
clumsy
cat’s whisker, and the weak signal could only be listened to
by one
person at a time with headphones. Very quickly the crystal set began to
be replaced by valve radios with loudspeakers, powered by battery (see
the picture from 1923).
In World War II,
crystal sets were
used by prisoners of war in prison camps to listen to news from home.
As
they were often badly treated it was hard to get all the right parts to
build the set.
By this time crystal sets were no longer used in the home. Instead radios like the attractive 1937 model in the picture were being used. Nowadays people only use crystal sets as a hobby. There are various different kits available on the market (see websites in the references below).
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| Photograph
Of A
Crystal Set From 1923 [from Pageant Of The Century - Odhams Press] Crystal sets were primitive instruments used for 'listening in', and were fitted with the now famous cats whisker. Listening was done though a pair of headphones which meant that only one person could listen at a time. |
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| Photograph
Of a
1923 Radio [from Pageant Of The Century - Odhams Press] Later valve amplification could be added to radios which allowed them to power a loudspeaker so that everyone in a room could listen in. |
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| 4 - HOW
I BUILT MY
CRYSTAL SET The crystal set is
a fun and easy
thing to build.
Next
the
earth.
For
this I
drilled another
hole in the ceiling and fed another wire through and out of an air vent
at the other side of the house (see previous paragraph). I attached
this
wire to the metal frame of my swing. This is a good earth because its
poles stick deep into the ground.The first thing I had to do was put up an aerial and earth. For the aerial I drilled a hole in the ceiling and fed wire through the hole. Then I went into the attic and took the wire to the other end of the attic, fastening it to rafters as I went. When I got to the other side I fed the wire out of an air vent to the outside of the house. I then went outside tied wire to a nearby tree and joined it up to the wire coming out of the air vent. This gave me an aerial of about 25 metres. The coil used
enamelled copper wire
wound on to a piece of plastic pipe with a diameter of 5 cm. There were
120 turns of wire. Every 10 turns I made a loop on which a crocodile
clip could be fixed. See the picture below:
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| Photograph
Of The
Coil Showing The Tapping Points & Crocodile Clips |
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| The
Tuning
Capacitor - Being Carefully Adjusted |
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For the crystal set
itself, I first
had to plan what I would be using and where the pieces would be placed
(see picture and the plan drawing). I was using the circuit
shown
above. I built the crystal set on a wooden board about 20cm
by
15cm. I drilled 4 holes 4cm apart. I put screws with cup washers in
each
hole and fastened the wires of the parts of the crystal set and the
aerial and earth wires under the cup washers. I fastened the
capacitor to the board using Meccano brackets and screws. The
coil
was fixed to the board using glue. The earpiece plugged into a socket
which was fastened to the board using a thunderbolt shaped piece of
Meccano.
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| Drawing
Showing
Layout Of Components |
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| 5 - THE
RESULTS I
OBTAINED At first all I
could hear was a
foreign station. But then, I tried late at night and could sometimes
hear a station from Florida in English! By tuning the
capacitor
and moving the crocodile clips up and down the coil I managed to
receive
a few foreign stations on Short Wave. What I really wanted was to tune
in to Medium Wave. I wanted to receive English stations like Radio
Scotland and music stations. I tried everything including a longer
aerial and using different parts but to no avail. I came to the
conclusion that I could not get a strong enough Medium Wave signal in
Northerly area of Scotland where we live.
Here is a picture of me operating my crystal set: |
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Photograph
Showing
The Crystal Set In Operation
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| 6 -
WHERE I FOUND
THE INFORMATION The History Of Crystal Sets Book: The Pageant of the Century, Odhams Press, 1933. www.oldradioworld.de/gollum/dhistor.htm How I Built My Crystal Set: Web page describing how to build a crystal set: http://www.mds975.co.uk/Content/crystalsets2.html
(THIS
SITE) Book: "Making A Transistor Radio" written by Rev. G.C. Dobbs, Ladybird, 1972 Kits Are Available From: www.midnightscience.com/kits.html www.oldradioworld.de/gollum/xkits.htm 1N34A.com - crystal radio parts, including litz wire is http://1n34a.com Other Hobby
Websites: Dave Schmarder's Crystal Set Pages http://www.makearadio.com/crystal/index.php
http://www.makearadio.com More
Crystal Set Links here >> |
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7 -
QUIZ QUESTIONS
CRYSTAL SET QUIZ QUESTIONS:
1. What is a crystal set? 2. When were the first crystal sets sold? 3. Name 3 essential parts for a crystal set. 4. What does the earth do? 5. Does the coil pass signals of low frequency or high frequency? 6. How far apart were the screws on my crystal set? 7. What happened when I made the aerial longer? 8. What is this an anagram of: i a c c p r o t a? (ANSWERS ARE AT THE BOTTOM OF THE
PAGE)
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PARTS
THAT ARE
REQUIRED
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| A Superb
RGD Valve
Radio from 1937 - carefully restored in 1994 by Roddie Rankin |
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With thanks to Kenneth and Roddie Rankin for sending in this excellent article and photographs! |
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QUIZ
ANSWERS
1. The first kind of radio 2. 1922. 3. Coil, diode, capacitor, earpiece, aerial, earth. 4. Gets rid of signals you don’t want. 5. Low. 6. 4 cm. 7. It did not make much difference. 8. Capacitor.
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No
AM radio stations or transmitters in your locality or country?
 Has your
local medium wave broadcast station closed or been moved to VHF/FM or
Digital? Don't worry. You can
still build and experiment with crystal sets and TRF radios by
also buying
or even building a simple low power AM transmitter. So, not only can
you use your
crystal sets but you can also run your own radio
station that can be heard in and around your home - playing the music
or programmes that you want to hear!
SSTRAN
AMT3000
Superb high fidelity medium wave AM transmitter kits from SSTRAN.
Versions available for 10kHz spacing in the Americas (AMT3000 or
AMT3000-SM) and 9kHz spacing in Europe and other areas (AMT3000-9 and
AMT3000-9SM). Superb audio quality and a great and well
designed little
kit to build: http://www.sstran.com/pages/products.html
 http://www.sstran.com/ Other AM transmitters available:
Spitfire
& Metzo Complete, high quality ready built medium wave AM
Transmitters from Vintage Components:
http://www.vcomp.co.uk/index.htm Vintage Components offer a choice of the high quality Spitfire and Metzo transmitters: SPITFIRE AM Medium Wave
Transmitter with 100 milliwatt RF output power:
 METZO AM Medium Wave Transmitter with built in compressor:  AM88 LP A basic AM transmitter kit from North County Radio. http://www.northcountryradio.com/Kitpages/am88.htm |
LINKS:
BOWOOD ELECTRONICS - A friendly, helpful and very speedy source for many of your electronic components at prices that won't frighten your wallet!
THE FOXHOLE and P.O.W RADIOS - Simple crystal set receivers used by soldiers during the war and by prisoners of war (P.O.W.'s).
VINTAGE COMPONENTS - A great resource for crystal sets, components, valve radio kits and medium wave AM transmitters!
6V6 - Electronic Nostalgia and Vintage Components
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