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Amplifier antenna question

davenn

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So the Wikipedia article on envelope detector is wrong? Or do you mean that yes resistance and capacitance are needed in addition to the diode or crystal, but usually the internal resistance of the wires and the capacitative reactance of the wires is enough?

show me the wiki link you referred to please.

you just need a diode to detect the AM radio signal. You would usually have a capacitor and inductor in parallel with each other in front of the diode to be your tuned circuit but they are not part of the actual audio detection. out of the diode you get audio to go to the crystal ( high impedance ) earpiece


Oh really, then it is impossible to connect your guitar amp to a speaker with a cable without a RF modulator. This is a false statement. So I don't think it is the case that audio frequencies can not be made into electromagnetic waves. Otherwise there would be no such thing as an electric guitar because the electric guitar pickups convert the sound waves on the strings into an alternating sinusoidal wave.

no you are incorrect.

The guitar pickup DOESNT pick up the sound waves from the vibrating string. The metal string moving in the magnetic field generats a current flowing in the picup coil
try a pickup on a classical nylon stringed guitar .... you wont get anything!!!


In addition, if RF near audio frequencies did not exist, then that would mean that 60Hz AC power transmission would be impossible so you would have no power for you computer allowing you to view this web page, unless you lived within half a mile from an Edison power plant and payed an arm and a leg for electric power, which Edison doesn't care that it can only go half a mile he only cares that you are paying him an arm and a leg for electric power.

none of that makes any sense and isnt the way power transmission happens .... it has nothing to do with it being 60 Hz or any other freq as a RF signal


dietermoreno ..... I wonder how old you are ? how much schooling in basic physics and electricity you have had ?
you have quite a few misconceptions in most of your statements that show that you really havent been taught correctly ot at all, or didnt understand what you were being taught.

but stick with it in here and read and learn, it will fill in a lot of gaps in your understanding :)

Dave
 
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davenn

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OK this is probably the wiki article you were referring to...

http://en.wikipedia.org/wiki/Envelope_detector

that first section and the accomp. diagram with the resistor and capacitor after the diode isnt even referring to audio detection from a RF signal. Its actually referring to Envelope detection of an Audio signal

in a basic crystal set radio receiver, there is no resistor or capacitor after the diode :)
the resistor would only be detrimental and drop the signal level. The capacitor is sometimes used for filtering any remaining RF on the output of the diode

have to go to work now but I will expand on the receiver as soon as I can

Dave
 
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dietermoreno

Dec 30, 2012
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show me the wiki link you referred to please.

you just need a diode to detect the AM radio signal. You would usually have a capacitor and inductor in parallel with each other in front of the diode to be your tuned circuit but they are not part of the actual audio detection. out of the diode you get audio to go to the crystal ( high impedance ) earpiece




no you are incorrect.

(1) The guitar pickup DOESNT pick up the sound waves from the vibrating string. The metal string moving in the magnetic field generats a current flowing in the picup coil
try a pickup on a classical nylon stringed guitar .... you wont get anything!!!




(2) none of that makes any sense and isnt the way power transmission happens .... it has nothing to do with it being 60 Hz or any other freq as a RF signal


(3) dietermoreno ..... I wonder how old you are ? how much schooling in basic physics and electricity you have had ?
you have quite a few misconceptions in most of your statements that show that you really havent been taught correctly ot at all, or didnt understand what you were being taught.

but stick with it in here and read and learn, it will fill in a lot of gaps in your understanding :)

Dave

(1) Oh okay that makes sense. That explains why guitar pickups don't pickup sound at all when you sing into them but pick up guitar string movement. The guitar pickups would have to be dynamic to have sound waves generate a force oscillating the magnetic field which generates oscillating electric current. The dynamic part of the pickup-string circuit is the strings. The strings are moving in and out of the magnetic field of the inductors of the pickups, generating alternating current. The strings do make a quite audible sound that is the same sound wave frequency as the electro-magnetic wave generated. The strings have no current to them and the pickups have no current to them, that is unless your house doesn't have a GFI outlet next to where you are practicing. I have been shocked before playing guitar in a friend's house which is an old house built in the 1950s that doesn't have GFI outlets. If I touch the strings of my guitar while my guitar is plugged into the amp if I stand within a few inches of the other guitarist the local ground of the guitar amp between the two guitar amps uses my body as local ground since the objective of an AC current is always to search for ground to flow to.

(2) I didn't say that 60Hz power transmission is a carrier wave. Power transmission is not a signal, its power. The amplitude isn't representing sound, the more time the amplitude is at a peak the greater the rms power is. So having a frequency of 10Hz would be 6 times less efficient but no higher frequency than 60Hz is needed to make devices work similar to if they were powered by DC.

(3) I am 21 years old. At a community college I took algebraic based physics for mechanics, electricity, magnetism, and optics. We skipped the chapter on alternating current because the instructor told me that AC requires the magic of calculus to truly understand since it has an instantaneous rate of change and this is an algebra based physics course. I am in Calc I now. I don't know that much about physics, electronics, or math and I don't need to know that much about those subjects because I am studying in the medical field rather than the engineering field because I'm not good at math and I don't like doing math because I'm not good at it.




(1) OK this is probably the wiki article you were referring to...

http://en.wikipedia.org/wiki/Envelope_detector

(2) that first section and the accomp. diagram with the resistor and capacitor after the diode isnt even referring to audio detection from a RF signal. Its actually referring to Envelope detection of an Audio signal

(3) in a basic crystal set radio receiver, there is no resistor or capacitor after the diode :)
the resistor would only be detrimental and drop the signal level. The capacitor is sometimes used for filtering any remaining RF on the output of the diode

(4) have to go to work now but I will expand on the receiver as soon as I can

Dave


(1) Yes it is.

(2) Oh. There is disambiguity in Wikipedia. It didn't specify that the circuit was for audio rather than radio. Wikipedia must have assumed that no one cares about envelope detectors for radios anymore because everything is going digital now so envelope detectors are no longer used in radios.

(3) Oh okay that makes sense. There is no need to have an RC circuit after the diode or crystal because the signal has already been tuned to before being demodulated and in crystal radio there is no amplification so adding a resistor would lower the audio volume. but there could be oscillator circuits after the diode (to remove any remaining RF, to remove mains hum, to equalize the audio) if mulitple gain stages are used in a more real world radio, rather than the idealized crystal radio which was okay when the tube hadn't been invented yet or was okay when all you have to build a radio is some wire and some tin cans and some pencil graphite.

(4) Okay thanks for attempting to teach me.
 
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