Features
The Basics of Radio Reception
Written by Bryce Ringwood   
Wednesday, 20 October 2010 22:59

 

Generating and receiving a signal

A radio transmitter generates rapidly varying electric voltages and currents in a conductor. If these are connected to a suitable radio antenna, then an electromagnetic wave is produced. According to the manual for one of my receivers, electromagnetic waves have frequencies of 20000 Hz and above, but I think they are merely referring to what is practice for most communications.

Last Updated on Wednesday, 06 November 2013 10:29
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Help -My Crystal Set Won't Work! PDF Print E-mail
Written by Bryce Ringwood   
Tuesday, 05 November 2013 11:37

My first crystal set didn't work either. At least, not at first. That must have been many years ago in the 1950's. Nowadays, there are many more reasons why a set won't operate than there were then – as we shall see. (More Illustrations to follow...please be patient!)

Last Updated on Thursday, 19 December 2013 15:56
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Shortwave Radio
Written by Bryce Ringwood   
Wednesday, 16 February 2011 11:38

Early Radio, prior to World War 1 focussed on long and medium wave transmissions. These cover from approximately 10kHz to 1600kHz. Broadcast long wave transmissions cover from approximately 150 to 300kHz and medium wave broadcast from about 500kHz to 1600kHz. Transmissions on these frequencies are carried principally by a “ground wave” during the day and by a “sky wave “ toward evening and at night time, where the signal can cover greater distances because it is reflected from the ionosphere.

Last Updated on Tuesday, 08 October 2013 13:24
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The Superhet PDF Print E-mail
Written by Bryce Ringwood   
Sunday, 14 November 2010 21:50

The Superheterodyne Receiver or 'Superhet' was invented by U.S. Army Major Edwin H Armstrong in 1918 in France during World War 1. Almost all the radios that you have ever seen are superhet receivers. (The exceptions being the crystal set and regenerative receiver projects on this web-site. The fremodyne is a type of superhet.)

Last Updated on Thursday, 08 August 2013 15:22
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Example Superhet Circuits PDF Print E-mail
Written by Bryce Ringwood   
Wednesday, 19 September 2012 21:39

This article provides a description of some typical radios you will never encounter - but at some point you may think you have! The first is from the 1936 RSGB Radio Amateur's Handbook. You can click on the images to download a higher-quality .pdf image.

Last Updated on Thursday, 08 August 2013 15:02
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Guide to Radio Valves PDF Print E-mail
Written by Bryce Ringwood   
Thursday, 28 October 2010 08:41

Radio valves are the active components of old wireless receivers. These are the devices that amplified the signal, converted it and drove the loudspeaker. In the transmitter, they generated and amplified the transmitted carrier wave and impressed speech on to it, so that a broadcast could be transmitted. This article describes some of their history, what they are and how they work.

Last Updated on Wednesday, 07 August 2013 13:48
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Rough Guide to (Mostly) Old Transistors Print E-mail
Written by Bryce Ringwood   
Sunday, 16 January 2011 11:20

Transistors are small electronic devices that can amplify small electric signals and can therefore perform a similar function to that of radio valves in radio receivers and transmitters.

Last Updated on Thursday, 13 September 2012 11:38
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Dial Cords and Drives PDF Print E-mail
Written by Bryce Ringwood   
Friday, 18 April 2014 17:40

Radios have a dial drive mechanism to translate motion of the tuning knob into motion of the dial pointer and increase the number of turns required to move the vanes of the tuning capacitor. A system of cords and pulleys is used to move the dial pointer horizontally. This article explains how to reair broken drives and the principles of operation.

The simplest radios do not have a dial drive. The tuning knob connects straight on to the tuning capacitor and a pointer on the knob points to the frequency marked on the radio cabinet. Many transistor radios adopt this simple system. At the other end of the (er.) scale we have complicated arrangements to make tuning easier for the user. Such complexities are by no means confined to military and "communications" type receivers.

Last Updated on Saturday, 19 April 2014 16:51
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Batteries PDF Print E-mail
Written by Bryce Ringwood   
Sunday, 04 August 2013 13:24
   

This article could save you thousands  of Rands per year! Supermarkets and pharmacies have hordes of batteries on display at the checkout – and most people take a pack of alkalines because they are well 'branded' and advertised, regardless of what they are going to be used for. If you can't be bothered with the text, then jump to the summary at the end and deal with the details later.

Safety first: Batteries contain dangerous chemicals. They also contain a huge amount of energy. Please observe safety tips. I am not responsible if you poison yourself or blow yourself up.


Batteries, i.e. Dry Cells, Accumulators and rechargeables represent portable power and convenience, generally at a high cost compared to mains electricity. In books on batteries, the term Primary Battery is used to refer to non-rechargeable and Secondary Battery to rechargeable cells.  I'm going to mention some archaic batteries because you may encounter references to them in old instruction manuals and wonder what they were. Whilst on the subject of archaic batteries – we might as well see how they were invented.

 

Last Updated on Sunday, 02 November 2014 18:10
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Printed Circuit Construction and Repair PDF Print E-mail
Written by Bryce Ringwood   
Monday, 03 November 2014 14:55
Printed circuit construction uses a thin sheet of material on which electronic components are mounted. The connections between the components are made from copper tracks on the board material, rather than the older method of wiring between each part. If you take almost any modern appliance apart, you will see the circuit board, often a small brownish coloured board with a few components sitting on it. The pins on the components go right through the board and are soldered to tracks on the other side. If you look at a computer printed circuit board, you will see very tiny components soldered to tracks on top of the board. This is a "Surface Mount Board", as opposed to "Pin-in-hole".
Last Updated on Wednesday, 05 November 2014 12:04
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Capacitors
Written by Bryce Ringwood   
Friday, 02 November 2012 11:39

Capacitors are used in electric circuits to store electric charge. In old radio books they are called condensers. They are different words for the same thing.

Early use of capacitors

The first experimenters were interested in storing electrostatic charges. Nearly everyone in the South African highveld knows all about static electricity through the numerous elecric shocks experienced in the dry season due to electic charge building up on our bodies. This happens because when we move, excess electrons are removed from our skin and clothing by the dry air. Then when we put our metal key in a grounded car door - the electrons flow from the metal door to our hands via the key.

Last Updated on Sunday, 07 December 2014 13:59
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