Low Frequency Vco

[DMW]

Hi

I am trying to make a frequency response analyser within the range of 0 to 10Khz. I am looking for a Vco which my microcontroller can interface with to create an sine wave output between 0 and 10khz [to be fed into a amplifier].

I have been looking at Vco's rather than DDFS's as I hear DDFS's are very hard to setup, however I am having problems finding any Vco's that will operate at the lower frequency's, can you advise me in any way or surest an IC?

Many Thanks
Dominic

 

[JimB]

DDFS ? Direct Digital Frequency Synthesiser?

They are not hard to set-up at all, just a few lines of code and the job is done.

Have a look at the AD9850, athough it has probably been supeceeded by now. This can give an output from 0 to about 50Mhz in 0.03 hz steps.
Have a look on the Analog Devices website for the latest DDS chips.

As for a VCO, I think it would be difficult if not impossible to go from 0 to 10 khz in one range without using a heterodyne technique, which makes a DDS look like the ideal solution, especially as you are driving it with a microprocessor.

JimB

 

[DMW]

Hi, thanks for the reply, yeah I had a look at the AD9833 a few days ago, they seem like good IC's but if there was a Vco avalible I would prefer to use that, thanks anyway .

 

[Space Varmint]

Hi

I am trying to make a frequency response analyser within the range of 0 to 10Khz. I am looking for a Vco which my microcontroller can interface with to create an sine wave output between 0 and 10khz [to be fed into a amplifier].

I have been looking at Vco's rather than DDFS's as I hear DDFS's are very hard to setup, however I am having problems finding any Vco's that will operate at the lower frequency's, can you advise me in any way or surest an IC?

Many Thanks
Dominic

This is one of my favorites. You will need say a 1 inch ferrite toroid for the coil at the frequency you wish to use. I cut this out of a PLL circuit I recently made. So you won't need Q3 & Q4.

 

[Roff]

This is one of my favorites. You will need say a 1 inch ferrite toroid for the coil at the frequency you wish to use. I cut this out of a PLL circuit I recently made. So you won't need Q3 & Q4.

Good luck at getting an LC oscillator to run at very low frequencies.

 

[Space Varmint]

Good luck at getting an LC oscillator to run at very low frequencies.

Like I said, you need a 1 inch ferrite toroid. I built one that has a beautiful sinusoidal wave shape. It used electrolytic capacitors in the tank and feedback path.

For a VCO at those freqs it would be necessary to place more than one varactor in parallel.

 

[Nigel Goodwin]

We're off again!

 

[Roff]

Like I said, you need a 1 inch ferrite toroid. I built one that has a beautiful sinusoidal wave shape. It used electrolytic capacitors in the tank and feedback path.

For a VCO at those freqs it would be necessary to place more than one varactor in parallel.

You are such a pie-in-the-sky BS'er. Put your money where your mouth is! It's easy to say, "Oh, just use a ferrite toroid and some electorlytic caps and a bunch of varactors, and it will work". If you post a working design of an LC VCO that will cover the audio range, I will publicly state on this forum that "I am not smarter than a 5th grader!"
Edit: It has to put out a low-distortion sine wave.

 

[DMW]

So a DDS is the way to go? thanks