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Questions about VCOs capabilities

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Member level 3
Oct 31, 2006
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I want to learn about Voltage Controlled Oscillators. I'm new to analog electronics, and basically, i'm trying to achieve a simple radio emission either for linking computers or controlling stuff from my computer. But that's still far away, i'm sure :) I've looked over teh intarw3b, but haven't found anything of real use.

First, how quick can a VCO go? low speed ones are found often (as schematics), but if i looked in a higher band 900, 1Ghz, or so - I can't find any. Are those constructable by beginners?

Can a VCO be used to attain a variable emission frequency (like FM modulation, but I can change the frequency i'm using) ? If yes, what would be the quality and difficulity to build such a device?

I know to work with pics, can a pwm signal, transformed into an analog voltage be used to control the freq, for example?

If i want to attain a range of frequencies, covering a spectrum, how is that done? Can it be done except sweeping? (Of course, not by using a device for each component of the range)


different frequencies can be get by controlling control voltage of VCO,range will depend on type of vco used.

Re: VCOs

Depends on which type of VCO you are looking for.
If it is an audio VCO, an IC as XR2206, MAX038 and so on can solve easily your problems.
If the VCO is in a GHz range, ( as I suppose ) it is not intended for beginners, any lenght of wire acts as inductor ( or capacitor ) and the parameters of the transistor are not as you are studied at school.
Are some VCO in the range you have indicated made by mini circuits and more other companies ( murata, toko, etc ).
From the first you can also by small quantities at fair price.


Re: VCOs
Look for microcontollers with RF interface, like rfPIC , ATrf ... , and here:

**broken link removed**

This way you will only need to configure the chip for a particular frequency, modulation, bitrate, design/use a datasheet schematic for the antenna circuit.
Design and construct carefully the RF part, minimizing the stray elements.

The TI chips for <1GHz(like CC1100) can transmit at 500kbps and are very cheap, so cheap that I would like to test one soon - there are many nice aplications for a RF transceiver and designig your own TRX it's quite hard to get that data rate.

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