hi.

can anyone pls tell me the best and simplest way to generate square waves with frequency of around 20-50 Mhz .. i am thinking of using a crystal oscillator but i think it wont be that easy.. i will be also needing an amplifier circuit for it..
can anyone pls help me with this? a circuit or reference will be of great help

thanks

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hi,
For 20MHz buy a, SG531P 20MHz oscillator module.
Get the data sheet

Look here: http://www.ece.rutgers.edu/~ece428/Datasheets/SG-51.pdf

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Do you need just a single frequency, or do you want an adjustable frequency? If it's just a single frequency, go with an oscillator module as suggested above.

Also, what kind of amplifier are you envisioning? just a buffer or a voltage or power amp?

 

At those frequencies your "square waves" will have a decidedly rounded appearance. Without careful layout and impedance matching they may also ring like a bell!

 

k.. heres what i am planning to do.....

i want to make a kind of local positioning system. it will work with the same fundas of gps with thte only difference of using rf transmitters instead of satellites. i need mhz frequency generator cause i want to send data after modulating it on the carrier wave (this 20Mhz square wave) using any of the shift key method. i want to have a range of around 1-3 kilometers.

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yes a variable frequency oscillator willl be best 'if' its not that tough to make or too costly (ie < US$10-15)

for the amplifier.. i want to use it to boost the signal strength so that it can be received as far as possible with least probability error....

from where can i get a schematic of such an amplifier or what should i be googling for?

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This guy has some really good RF projects:
http://hem.passagen.se/communication/6mpa.html
Here is a crystal controlled 50Mhz transmitter:
http://hem.passagen.se/communication/buggtx.html
I particularly like his 0-250mhz signal generator. I might even try building this one day. Will make a nice piece of test gear with a few mods:
http://hem.passagen.se/communication/rfinject.html

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What county are you in? Most have laws against that sort of range and heavy fines for violations. Plus there are a limited number of frequencies available for amateurs and 20MHz to 50MHz is probably not an available frequency, and square waves are probably right out due to harmonics.
Typical unlicenced transmitters are often limited to a few meters and far less than a watt of power.

Add to that GPS is a pretty sophisticated system with very accurate clocking.

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I would agree, I doubt there's any country where such a scheme wouldn't be highly illegal?.

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i am in india... the place where i will be performing my project is an educational institute located on the outskirts of a town (ahmedabad). we do have laws in our country but they are not very strict about it, especially in remote areas. moreover our institute does hold the license to use the amateur band. in fact, we have been using it for past couple of years for experimental purposes.


ya now.. the square wave generation is completely out of question. what now i need is an oscillator which can generate sine or cosine waves at frequencies of around 20-30Mhz.. are there any readymade ics available?

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It doesn't matter if you are in a remote location, it's still highly illegal!, bear in mind 100mW at 20Mhz could travel thousands of miles!.

But I suggest you look up PLL (Phase Looked Loop).

And why not use laboratory signal generators to try your scheme?.

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k... i looked up in our countrys frequency spectrum division chart.. my college has the license to use the amateur wireless telegraph station license grade 2... in which its legal to transmit signals at 25W power excepth fo r the last one - 5 watts

there are three frequency range for this.. 3.8-3.9,7-7.1,144-146 (all in Mhz)

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Very apt Nigel, the purpose is not to design a RF signal generator , but only to transport a signal over a distance and the lab signal generator can well be used.

ujjvalshah gains time to do other (the mainpart) of his project. most probably 27MHz also can be made use of under the resitricted power levels, i hope..

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Those are some of the amateur bands, and their use is restricted to specific modes and usages - notice they don't cover a large block from 20MHz to 50MHz as you were asking about!. I also don't think your intended use meets the licence conditions?.

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thanks nigel and sarma.. i will definately use the lab generators for testing purpose. but as a project i need to make my own oscillator.

so for time being leave out all the legal stuff and pls just guide me to make an oscillator with frequency of anything around 20-50Mhz and the output of which should be a sine/cosine wave..
arent there any readymade ics available?,, ,like the one SG531P 20MHz oscillator module posted earlier in this thread by ericgibbs which generates square waves.. are there any ics that can generate sine waves?

hey nigel,..can you pls throw some more light on ppl for me?

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