Mhz frequency generator

[ujjvalshah]

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

 

[ericgibbs]

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

Look here: https://www.electro-tech-online.com/custompdfs/2007/09/SG-51.pdf

 

[pc88]

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?

 

[Papabravo]

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!

 

[ujjvalshah]

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.

 

[ujjvalshah]

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?

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?

 

[kchriste]

This guy has some really good RF projects:
https://hem.passagen.se/communication/6mpa.html
Here is a crystal controlled 50Mhz transmitter:
https://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:
https://hem.passagen.se/communication/rfinject.html

 

[blueroomelectronics]

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.

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.

 

[Nigel Goodwin]

What county are you in? Most have laws against that sort of range and heavy fines for violations.

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

 

[ujjvalshah]

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?

 

[Nigel Goodwin]

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?.

 

[ujjvalshah]

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?.

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)

 

[mvs sarma]

It doesn't matter if you are in a remote location, ............

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

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

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..

 

[Nigel Goodwin]

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)

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?.

 

[ujjvalshah]

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?

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

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

 

[Mike - K8LH]

are there any ics that can generate sine waves?

You might consider a DDS IC (Direct Digital Synthesis) + amplifier + filter.

I purchased the kit below for around $30 for use with a microcontroller but I believe you can also use PC software connected to it via the parallel port.

**broken link removed**

https://amqrp.org/kits/dds60/index.htmlDDS-60 Kit from AmQRP

(A 0-60 MHz coverage VFO with built-in amplifier and variable output level from 0 to 4V p-p.)

 

[Nigel Goodwin]

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

If you google for it (using PLL and NOT PPL) you'l get all the information you require.

 

[Hero999]

You want sine waves not square waves.

Also I would consider buying pre-made modules rather than stuffing it together yourself.

 

[ujjvalshah]

i googled for pll and its ics and i found out that they will definately serve my purpose.. thanks nigel

but of all the ics i found none of them had sine wave as the output of the vco output.. they all had square waves.. (i have also read that some pll can give output in sine waves too.. but couldnt find them)

You want sine waves not square waves.

Also I would consider buying pre-made modules rather than stuffing it together yourself.

i found some ics which actually generate sine waves directly but their maximum range is 200KHz only

so can anyone pls help me in finding a pll ic which has sine wave as output and of operating range in 20MHz ????

 

[Nigel Goodwin]

i googled for pll and its ics and i found out that they will definately serve my purpose.. thanks nigel

but of all the ics i found none of them had sine wave as the output of the vco output.. they all had square waves.. (i have also read that some pll can give output in sine waves too.. but couldnt find them)

IC's generally don't give squarewave outputs, you use a voltage controlled LC oscillator, with a PLL control system.

i found some ics which actually generate sine waves directly but their maximum range is 200KHz only

so can anyone pls help me in finding a pll ic which has sine wave as output and of operating range in 20MHz ????

The DDS60 kit mentioned above sounds exactly what you want!.