Demodulation

[alfa88]

How am I able to do a AM transmitter and receiver ? My friend will be doing the AM transmitter and I am responsible for AM receiver. Any suggested circuit ?

No microcontroller is allowed

For the life of me I can't recall where I found this transmitter schematic. I didn't have a variable cap. so I used a fixed value I had sitting around. The range wasn't all that good but then again I slapped it together with no regard to lead length, noise, etc.

 

[duke37]

An old chip, the ZN414 has been used for a TRF receiver, this is now absurdly expensive but has been replaced by MK484 (cheaper) and TA7642 (cheap). It needs a power supply which the crystal set does not.
This could drive an amplifier or headphones.

 

[vick5821]

For the life of me I can't recall where I found this transmitter schematic. I didn't have a variable cap. so I used a fixed value I had sitting around. The range wasn't all that good but then again I slapped it together with no regard to lead length, noise, etc.

What can I used to made the antenna ? Can it be a single core wire ?

Thanks

 

[vick5821]

Something like that with a preamplifier in the output maybe ?

Pretty much same as john's diagram

Any further info about this typee of circuit ?

Do we actually have vari cap ?

What is the expected output here ?

Thanks !

 

[davenn]

What can I used to made the antenna ? Can it be a single core wire ?

Thanks

yes it can be a single wire off the bottom end of the coil ... the L1/C26 junction, you should have a variable capacitor across ( in parallel with) the coil. It gives you the ability to tune the transmitter to a particular frequency. The antenna wire can be anything up to a couple of metres long

Dave

 

[vick5821]

yes it can be a single wire off the bottom end of the coil ... the L1/C26 junction, you should have a variable capacitor across ( in parallel with) the coil. It gives you the ability to tune the transmitter to a particular frequency. The antenna wire can be anything up to a couple of metres long

Dave

Are we able to purchase a varrible capacitor ? I doubt my University lab have it ><

Thanks

 

[BobK]

If this is a one-off transmitter receiver project, you don't need a variable capacitor, you could tune it to a fixed frequency with a few caps in parallel.

Bob

 

[vick5821]

If this is a one-off transmitter receiver project, you don't need a variable capacitor, you could tune it to a fixed frequency with a few caps in parallel.

Bob

What is the L1 ?

What should I search in google ? I need more information about this things. I am planning to do it.

Thanks !

 

[Electro132]

If this is a one-off transmitter receiver project, you don't need a variable capacitor, you could tune it to a fixed frequency with a few caps in parallel.

Bob

Can you show us what you mean in a diagram please?

 

[vick5821]

https://www.electronicspoint.com/attachments/8042d1367101382-demodulation-14184_158_1.jpg

Here is the picture. What is the L1 at the left side there ?

Thanks !

 

[CDRIVE]

That's dependent upon the value of 'C'....

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

http://www.1728.org/resfreq.htm

This does beg a bigger question though.

Chris

 

[vick5821]

which one do you mean ?

Thanks !

 

[dietermoreno]

I built a variable capacitor out of plastic loyalty cards in my wallet, aluminum foil, and 3 nails like this:

https://www.electronicspoint.com/va...rible-capacitor-fm-crystal-set-t259535p2.html

 

[CDRIVE]

which one do you mean ?

Thanks !

Which one what? Are you referring to the two caps in that circuit? If so we're referring to the tank cap. The cap across the phones is an RF bypass.

Tip: If you want to keep your sanity I suggest Ignoring anything posted by dietermoreno. He knows just enough to be dangerous to himself and anyone near him!

Chris

 

[vick5821]

Which one what? Are you referring to the two caps in that circuit? If so we're referring to the tank cap. The cap across the phones is an RF bypass.

Tip: If you want to keep your sanity I suggest Ignoring anything posted by dietermoreno. He knows just enough to be dangerous to himself and anyone near him!

Chris

I mean what is the L1 ? It's seems to be a transformer to me. And I can connect a speaker at the output ? What will I hear ?

Thanks !

 

[alfa88]

It is a transformer of sorts. It couples the signal from the antenna to a resonant tank circuit. The value of L1? Who knows? You could find one in a discarded AM radio in the form of a loopstick antenna; coils wound on a ferrite rod. Finding the capacitor value will take experimenting with alot of capacitor values, most likely in the pF range.
There will not be enough power to power a speaker. An earphone yes.

 

[(*steve*)]

L1 and C1 are chosen to be resonant at over the range of frequencies that you wish to receive.

The winding between the antenna and ground may be a simple as a few turns on the end of a ferrite rod (the same ferrite rod that the main part of L1 is on)

Here is a similar circuit which shows the component values you may be interested in.

 

[CDRIVE]

Let's talk about proper audio transducers for Crystal Radios. Conventional electromagnetic speakers are out of the question. Earphones, Ear-buds, etc are the order of the day but they must be high impedance. You can't use earphones that employ miniature speakers. In fact I don't even recommend 1KΩ ear buds, as they still require easily measurable power to drive them. Since Crystal Radios don't employ a power source or any active amplifier stages the earphone must be sensitive enough to be driven from the demodulated RF wave directly

Crystal earphones are unique transducers. They provide no DC path other than leakage which, for the most part, is insignificant. This puts them in the Electrostatic category. These are devices that respond to voltage while real part current (non reactive) is zero. This property makes them ideal for Crystal Radios because they dissipate negligible real power.

If you use a crystal earphone with This circuit you must also shunt the earphone with ~100KΩ - 1MΩ. This is needed to provide a DC path for the Detector Diode while keeping the signal load minimal.

Chris

 

[vick5821]

What type of question will normally been asked for Amplitude modulation and demodulation topics ?

What should I be clear about ?

Hope to get some guidance.

Thanks !

 

[CDRIVE]

What type of question will normally been asked for Amplitude modulation and demodulation topics ?

What should I be clear about ?

Hope to get some guidance.

Thanks !

Your question might win EP's 'Oddest Question Ever Asked' award. I'm not sure what you're asking. It only makes sense if your a student and want to know what your instructor might ask you about your project. As in: "Mr. Vick please explain the purpose of C1 to the class".

So, is this the general idea of what your asking?

Chris