FSK

[audioguru]

A simple FM detector will output different voltages for the two carrier frequencies, and you can easily convert it to logic levels with a comparator.

Yeah, any FM detector has a DC output shift caused by FM.
Even the AM receiver used by MStechca can have a DC output shift if it slope-detects the FM.

Many licence free modules use FSK, but they use AC coupling, which prevents a continuous DC output from the receiver.

Then the data can't have a string of highs nor lows. Therefore is their data coding called "Manchester" or "NRZ"?

 

[Nigel Goodwin]

Many licence free modules use FSK, but they use AC coupling, which prevents a continuous DC output from the receiver.

Then the data can't have a string of highs nor lows. Therefore is their data coding called "Manchester" or "NRZ"?

It can have a string of lows, and it does in the situation of no signal, but it can't have a continuous high - after a certain time the AC coupling makes it fall to low again (rather messily!). As you rightly say, "Manchester" or other "NRZ" coding can be used to get over the problem.

 

[mstechca]

Are you going to modulate a single RF carrier with AFSK audio tones, or are you going to somehow switch between two RF frequencis with FSK?

It would be nice if I used two separate carrier frequencies and transmit tones and receive them. In fact, I think that method is at least twice as fast compared to transmitting two tones on one carrier frequency.

and because the varactor trick you pointed out has some more success to it, I can use that to switch the frequencies. This is where the digital counter comes in handy :wink:

Don't worry Nigel, I'm not reentering that topic.

This guy here:
**broken link removed**
audioguru must be jealous, because my receiver works, even though he declares it as a "toy". My god, if I gave it to a young kid, he eat the ***n transistors :shock:

Good point!
FM is a very simple way to make FSK. But how would you detect it, it is DC modulation, isn't it?

I have made a VU meter that detects amplitude and lights an LED accordingly.

The problem is that MStechca's transmitter was an AM transmitter

How is it AM? I used and slightly modified the "miniature FM transmitter" found at the university of guelph.

Now he can't afford a real varactor diode...

It isn't the matter of affording it, it is the matter of wise shopping.
I shop at Sayal Electronics, because it is the cheapest store I go to.
They sell varactor diodes at $1 each. they sell normal 1N4007's at about 10 cents each. I would rather screw up 1 regular diode than 1 varicap.

Did anyone tell you that at least 1/2 of us are not real experts?

It is called "Experimenting".

Also he is using an AM receiver.

As long as I can receive almost anything with it, I don't care.

 

[audioguru]

The problem is that MStechca's transmitter was an AM transmitter

How is it AM? I used and slightly modified the "miniature FM transmitter" found at the university of guelph.

It is an AM transmitter that also produces a little FM.

The audio signal modulates the amplitude of the RF oscillator transistor producing AM. When a transistor is amplitude-modulated then its collector-emitter capacitance is also modulated since its reverse voltage is modulating. The transistor is used as a varactor diode to make a little FM. If you overmodulate it then the transistor saturates and cutsoff at the peaks, which really messes-up its FM.

Hee, hee. :lol: Is the range of your "toy" transmitter and "toy" receiver more than about 15 feet yet?