# Need help or resources for RF frequency generator design?

Discussion in 'Wireless & RF Design' started by electronice123, Oct 19, 2008.

1. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
304
0
I am working on a project in which I need to build a 0-10kHz frequency generator with a 50% duty cycle, with adjuatable gating & voltage amplittude. The frequency will go to a transistor which will then drive the primary side of a resonant transformer.

I plan on building the circuit using a 4046 VCO. I know how to build that part, but as far as the adjuatable gating and voltage amplitude I don't even know where to start, what would be required, and how to build it.

I can read diagrams and build circuits, but as far as designing them and knowing what I need to use I don't have much knowledge. I am just wondering where I can aquire this knowledge, or if anyone here can help me build this circuit.

Any help or recommendations would be greatly appreciated!!!

thank you everyone!

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
This is as dupilcate thread so I have removed the duplicate.

You refer to RF in the title but 0 to 10KHz is not RF. Did you need assistance with radio-frequency?

hgmjr

3. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
While you can broadcast at 10 KHz and lower, those frequencies are usually referred to as audio frequencies, as people can hear them.

Here is a link to a circuit that is very useful - http://wiredworld.tripod.com/tronics/signal_source.html. I would use it because it is easy to apply the triangle wave output to a voltage comparator to produce a variable duty cycle.

The adjustable amplitude is done by applying the signal to a potentiometer and using it as a volume control.

Resonant transformers are usually so because they work at a fixed frequency. Driving one with a variable frequency might be a challenge. What kind of power will it handle?

4. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
304
0
Ok.

I need the circuit to perform the following:

10V source voltage, 0-10kHz square wave 50% duty cycle, adjustable gating at 5, 10, 15, and 20 pulses, adjustable voltage amplitude output also.

I have already built the frequency generator out of a 4046 VCO, it's basically a 10V regulator, the 4046 chip, a 82K resistor, a .002 uF cap, and a 100K pot to adjust the frequency. I found this design in a book and thought it would be best as it produces a 50% duty cycle no matter what frequency you go to.

The only thing I do not know how to do is put in the gating circuit, and the voltage amplitude. I was thinking I could use an amp on the output to the transistor and then possibly a pot to adjust it for the amplitude like you said, I am not sure how strong the signal coming out of the chip will be or if the amp is needed though. I want the transistor to be adjustable from about 100ma-1A or so, I'm not sure what base current that would require. I guess I need to look up the datasheets for my transistor to find out.

Last edited: Oct 19, 2008
5. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
For that kind of gating, it would be convenient to apply the pulse train to a counter. When the preset number has been reached, disable another gate to stop the pulse train from going to the rest of the circuit. 4000 series CMOS might be simple to use, given the 10 volt Vcc.

As said before, driving a transformer over a wide range of frequency is very difficult. They become very inefficient. What is the circuit going to do?

Oct 14, 2008
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7. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
304
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The transformer is designed to work at a specific frequency. The transformer is used to charge a resonant tank circuit so I need the frequency to be adjustable so I can get as close to resonance as possible.

Later I want to build a circuit to detect and lock resonance in, but for now I'm just wanting to build the circuit with a manual frequency adjustment using the pot.

I have been told before as you said I can gate the circuit using counters and some AND gates, but I have no idea where to start or how to do that?

8. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
304
0
Thanks Farlander. That is a good reference, I will have to study it and see what I can learn.

thanks again