Basic Adivce/tutoring sought

Capacitors remember the past, resistors don't. The voltage across a capacitor is proportional to the total charge that has passed through it, since it last had zero volts across it. Or mathematically, V=Q/C. 1/C is just the constant of proportionality between voltage and charge.

If you look at this as a process, in time, rather than as a result, you can say that the rate of change of the voltage across a capacitor is proportional to the current passing through it. I=C*(dv/dt), where dv/dt means rate of change of voltage with respect to time, with units like "volts per second".

Think of a resistor as a device that enforces a fixed proportionality between voltage and current. Another way to look at ohms is to call them volts per ampere. Double the volts (electromotive force across the resistor) and the amperes through it (amount of charge per second) also doubles.

(replace?)

An inductor also remembers the past, but instead of having a voltage in proportion to total charge, it has a current proportional to total volt seconds. So it remembers how much voltage for how long has been applied to it, and that memory is represented by its current.

A capacitor and inductor in combination act something like a spring and mass act, mechanically to produce a resonance. When the spring is at maximum distortion and the mass is changing directions, but momentarily at rest, all the energy is stored in the spring. But when the mass hits peak velocity and the spring is passing through its relaxed state, all the energy is stored in the kinetic energy of the mass. The energy sloshes back and forth between spring and mass, twice per cycle, and the value of spring stiffness and mass determine the resonant frequency.

I'm not following the question. I think you are trying to combine several processes into one, and skipping too many steps. It is sort of like saying that if you can run a mile on one hamburger, how fast can you run if you eat a gallon of gasoline.

The FM transmitter combines radio frequency energy with audio by varying the frequency of a fixed energy carrier in proportion to the amplitude of the audio signal. Replacing the audio with something else does not change the power of the carrier.

The receiver separated the modulated carrier from all other frequencies (if it receives enough energy from the transmitter) and then discards all information about how strong the carrier is, and just responds to the frequency variations to recreate the audio signal in proportion to the frequency shifts. Doubling the power of the transmitter carrier allows this process to work over a longer distance, but does not change the volume of the audio at the receiver.

Reply to
John Popelish
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Greetings all

I hope I make sense, as I'm seeking some guidance through this, please. I'm trying to get to grips with some basic electronics. I know and have learnt the electronic math rules W = V x A ; V = IR , etc..

What I get stuck on is more "why would one use a capacitor in a circuit, why not a resistor?" I understand the functions that a part plays (sometimes not 100% correct) but generally eg: capacitor: takes in energy (voltage) and stores it, until it is released. Resistor: acts to slow down the voltage as like a form of friction. much like one lane of traffic compared to a 4 lane highway.

But what I don't grasp is why do we place a resistor with a coil to make a tuning circuit, why not use a capacitor. I'm trying to grasp what is it about the resistor, that makes the two components work and thus form a tuning circuit.?

For example: If I take an FM Receiver and Transmitter kit (wireless microphone kit or remote control kit), say I connect a 1 Watt power source to the Transmitter, (in place of the human voice on the microphone kit) what components will effect the Voltage and Amperage (v x a = W) in the receiver side, and should it be the same +/- 1 Watt and what would cause the decrease should there be a difference?

I thank you for your assistance up front,

Thanks Barry

Reply to
Roy Ingham

On Wed, 28 Sep 2005 18:29:49 +0000, Roy Ingham wrote: ...

Not necessarily - only if the receiver is designed to provide that power to the load from its own power supply. The actual amount of "power" sent from the transmitter to the receiver is minuscule.

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Good Luck! Rich

Reply to
Rich Grise

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Not generally, in a practical sense, considering that the energy in
the transmitted beam spreads geometrically when it leaves the
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Reply to
John Fields

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Picture this:

You have a large tank full of water in which is submerged a
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Reply to
John Fields

One of these sources can probably explain it better than I can:

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Good Luck! Rich

Reply to
Rich Grise

Firstly thank you for your reply it was helpful.

John Popelish wrote: > ....

So then the an issue of why a capacitor and a inductor / coil are used in combination is due the time "remberance" that both components have.

If a inductor was put with a resistor, then only the inductor would be aware of the time factor, while the resistor would not, correct?

Thus: frequency, (the tuning circuit = inductor with capacitor) which is time based, requireds all or both components to be time aware, right?

Do you know of an online source, that explains the time aspects of a capacitor. So far I have only come across the voltage storage principles of a capacitor, none mentioning the time rememberance factors?

I could be skipping steps, not sure? Ok, so let me rephrases this another way. Using a wireless microphone kit, with a tranmitter and receiver. Designed or should be used as follows: Human Voice -> Transmitter Receiver -> Tape Deck Using the wireless system I can now record what is said onto the tape deck.

Now making an assumption, lets replace the Human Voice with 1 Watt power supply and the tape deck with a Light Blub, thus giving:

1 Watt Power -> Transmitter Receive -> Light Bulb

Questions:

1) Would the Light blub be able to receive 1 watt of power, if not why?

2) If the light bulb was to receive power. How much would it receive, ans what would cause the loss if the power received is less than the 1 watt supplied.?

Thank you for your input John, your insight was helpful.

Barry

Reply to
Roy Ingham

This is why, together this pair is called a second order system.

Correct, and this pair makes up a first order system.

Frequency selective circuits can be made with just an RC or RL pair, but this kind of selectivity is just low pass (everything lower than some cut off frequency is passed through with minimal attenuation) or high pass (everything higher than some cut off frequency is passed with minimal attenuation) but it takes at least a second order system to produce resonance that act as a band pass filter.

The search key words might be [capacitor capacitance tutorial]. E.G.

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So far I have only come across the voltage storage principles

And you may not find such a description. The mathematical way to say "remembrance factor" is to refer to a function of time. The voltage across a capacitor is a function of current passing through it and time. The rate of change of voltage across a capacitor is proportional to the current passing through it. Current is charge per time. Rate of change of voltage with respect to time is a function of time. If the present value involves time, there is some sense of history in the present value.

In the voice receiver combination, the amplitude of the voice signal produces a proportional receiver output signal, even though the actual power in the receiver's output comes from its power supply, not from the voice. The voice provides a controlling signal that determines how the receiver's power supply is converted to a proportional copy of the original voice signal.

So the conversion of 1 watt going into the transmitter has no particular form implied to make it an appropriate control signal at the receiver. If the transmitter is designed to modulate its carrier energy with a few millivolts from a microphone, and you replace the microphone output with a 1 watt audio tone (say, a speaker drive signal) at the very least, the transmitter would produce a distorted modulation and be received as a distorted (like a fuzzed electric guitar) version of the original tone. At worst, the large audio power to the transmitter input would destroy the modulation circuit.

Power leaves the transmitter in all directions into space. Only a tiny fraction of that energy is picked up by the receiver. That tiny signal is amplified (a more powerful copy is created that matches the instant by instant variations of the radiated wave) with power from the receiver's DC supply. In a similar way, power steering copies the movements you make with the steering wheel, only with much more force capability, using power from the engine via the power steering pump.

The modulation (audio) information is recovered from that amplified copy of the radiated wave, and then that signal is probably again amplifier with more power from the receiver's supply before it comes out of the audio jack of the receiver.

Reply to
John Popelish

You are probably biting off more than you can chew at this stage. The concept of tuned circuits are not something that a beginner should start with, esp if you don't fully understand how a capacitor works yet. Start off with basic DC theory which involves resistors and voltages, and then move on to basic AC theory with Resistor and Capacitor (RC) circuits. Stuff like RC time constants, how a capacitor lets AC through but not DC, that kind of stuff. Then learn about inductors, and Resistor and Inductor (RL) circuits, and then you might be ready to grasp LC tuned circuits and other more complex AC theory. All of these are basic "building blocks" which you combine to make a circuit that does something useful.

I can recommend "Circuit Theory & Techniques" by Hans Goodman. Vol 1 and Vol 2.

Dave :)

Reply to
David L. Jones

In the same way that I can put human voice into the transmitter (microphone) and get the human voice out of the receiver to the tape deck (or house monitors). Can I not "transport or send" power/electricity from a transmitter to a receiver (not linked with the power required to operate)?

The 1 watt power source, is not the power source required to operate the transmitter, nor was I concerned about the power source(battery) to power the receiver. But rather the ability to transmit power from transmitter to receiver. I take it this is not possible?

Thanks again for all your help and input

Barry

Reply to
Roy Ingham

I read in sci.electronics.design that Roy Ingham wrote (in ) about 'Basic Adivce/tutoring sought', on Wed, 28 Sep 2005:

It's not exactly impossible, but it's so very difficult that it's not proved practical. Both Tesla and Yagi (he of the xylophone-like antenna) tried. In fact, Yagi invented his antenna for power-transmission experiments.

There has been speculation about transmitting power as microwaves from solar-powered satellites to ground, but there are huge problems, not least of which is ensuring that the power beam doesn't fry the nearest city when the satellite's guidance system is zapped by a solar eruption.

People have managed to steal a hundred watts or so from a nearby high-powered broadcasting station (think 50 kilowatts), but the receiving antenna had to be very large, and the people running the station could tell it was happening. so the FCC moved in rapidly to stop it.

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Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
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Reply to
John Woodgate

Actually it's done all the time with RFID systems, but maybe not in the ballpark that the OP imagined.

You need to be quite close to the transmitter, as the field falls off quickly.

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ciao Ban
Bordighera, Italy
Reply to
Ban

^^^^^ Oops... 1s

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John Fields
Professional Circuit Designer
Reply to
John Fields

Wow!! so much input, thank you

I didn't even think about the radiation of the signal from the transmitter, thus making it obvious that the receiver can only get a part of the signal.

For everyones input thank you.

Barry

Reply to
Roy Ingham

capacitors behave like springs

they don't

a typical tuning circuit uses a capacitor and an a coil

with a resistor and a coil you can make a filter circuit.

1 watt is way too much input to the microphone terminals, more like 1 microwatt. 1 watt into the power source (battery terminals) is quite a lot too,

the volume knob :)

or if you mean the strength of the radio signal received the antenna, is probably the main consideration.

there will be a decrease, as the 1 watt radio signal spreads out to cover more area it gets weaker like the way a distant lamp gives less illumination.

Bye. Jasen

Reply to
Jasen Betts

it's possible, just not practical. a "crystal set" am receiver is totally powered by the received signal, they typically need a large antenna, and only output into a earpiece.

energy is sent, but the energy sent is one millionth or less of the energy used to power a typical receiver... the energy sent is just used to carry the information - the voice.

if you put a louder input into the transmiiter you'll get a louder output from the receiver (within limits), but still the receiver is responsible for the energy in the output, the transmitter only for the content (information part)

Bye. Jasen

Reply to
Jasen Betts

David Jones gave very good advice- follow it and learn the basics. There is a hell of a lot between understanding of V=IR and radiation of signals and the intermediate steps are important.

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Don Kelly @shawcross.ca
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Don Kelly

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