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Author Topic: Simplest AM radio receiver  (Read 8420 times)
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Lancashire, UK
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What makes me think GM is in his element with this old technology ? 

No offence Mike, I'm one of your biggest fans really.
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Manchester (England England)
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Crystal sets were old technology when I was a lad.   smiley

I used to sell crystal sets to people when I was at school. That is where I came up with the ferrite rod tuning method, it was a cost down on the variable capacitor. I made the boxes out of cardboard and used to sell then for three and six ( 3/6 ) and it cost me about two shillings to make. Not sure what that is in new money.
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17.5p and 10p.  Buys b*gger all these days.  I'll bet there's an amateur radio ticket in your past somewhere......
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One over two Pi root LC gives you the resonant frequency. (sing it)

When nobody else is listening preferably... my landlady just gave me a O___o look as though I'm an escaped mental patient smiley-wink
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Manchester (England England)
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I'll bet there's an amateur radio ticket in your past somewhere.
G8HBR

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my landlady just gave me a O___o look

 smiley
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just got all the parts and made a Am radio. it worked! i used a 100pf cap and a inductor like you told me and tuned it using the rod method!
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Well done, I bet you are well happy.
Can you pick up many stations?
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i am as very very happy! thank you again! i thought id never understand how a LC circuit works but i do now! i can easily pick up 3 stations, but i used an op amp to amplify the signal, also the signal is also sometimes very noisy, how can i reduce this? capacitor?
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i next have to learn how fm circuits works. For another time i guess  smiley-grin
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The thing I like about a crystal set is that it uses no power, so using an op amp is cheating a bit.  smiley

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also the signal is also sometimes very noisy, how can i reduce this? capacitor?
The way to reduce this is to make the LC circuit have a higher Q. This Q is a quality factor and is related to how sharply the frequency response is defined. That means it picks up less of the other signals and more of the wanted signal.
Some capacitors will give a higher Q tuned circuit than others. Here ceramic capacitors are not so good, mica and polystyrene are much better. But the thing that affects the Q the most is the inductor and the grade of ferrite. For an explanation see:- http://en.wikipedia.org/wiki/Inductor
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Well yes, kinda cheating but i did get the crystal earpiece  smiley it did work but the volume was too low. I used an op amp only then i could hear the other two stations. hmm i see, it depends on the quality of components used. this method of transmission and reception can work with any frequency right? also i was trying to buy a 200pf trimmer cap for this but it seems there aren't any.
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also i was trying to buy a 200pf trimmer cap for this but it seems there aren't any.
Not as a compression trimmer but you can get a 500pF variable capacitor, but new they are not cheap.
There is this one:-
http://compare.ebay.co.uk/like/120824146657?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&cbt=y

But again there is this one:-
http://www.radioworld.co.uk/catalog/second_hand_520pf_medium_spaced_variable_capacitor-p-8916.html
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thanks again! yeah i saw that too. Also remember you said that the germanium diode is not necessary, and it could be used with a silicon rectifier, i tried the running circuit with a general purpose rectifier and it didn't work at all.
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A germanium diode needs 0.2V across it before it conducts where as a silicon diode need 0.7V. Therefore you need a much larger signal to make it work. Also a rectifier has a larger junction surface area which acts as a capacitor and suppresses the Q of the tuning circuit.
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thanks again! all queries have been solved smiley may i ask how do u have so much knowledge of almost everything related to electronics, i always see you answer on everything smiley  is there anything known as variable inductor? also can you guide me on how to make inductors of a specific value?
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