High resolution VCO
High resolution VCO
(OP)
Please help: What VCO would replace the Agilent E4422B (or equivalent) in the 2.000-2.300 GHz range? We are looking for a comparable high-resolution. thanks.
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RE: High resolution VCO
VCOs are voltage controlled oscillators. You would have to build a control loop to feed them the precise voltage required to achieve the frequency resolution that you need. That control circuit is called a phase locked loop, and the entire subsystem would be a frequency synthesizer. You would program the synthesizer's frequency with a serial digital word.
You would need a knowledgable engineer to design it for you. But you should determine exactly how fine a frequency resolution you need, as finer resolution means more complex circuitry. For instance, a 1 KHz resolution is much cheaper than a 1 Hz resolution.
RE: High resolution VCO
RE: High resolution VCO
thanks, but what's wrong with a having a high-resolution voltage supply to control the VCO (w/ voltage resolution high enough to match the sensitivity of the VCO)?
RE: High resolution VCO
The Agilent references to quartz. Therefore, I thought you should address the accuracy issue.
This leaves you with tuning speed, spur levels and the noise floor.
What are your actual requirements?
RE: High resolution VCO
I am tracking a cavity w/ a tuning speed that is most likely to be slow (seconds) for most applications. All I care is that nothing disturbs the oscillator to within 1-10 KHz (noise, spur) from the voltage set frequency,which I need set with ACCURACY to within 10-100 KHz to match the cavity normal mode.
RE: High resolution VCO
There are a lot of good books on VCO PLL. There are some practical concerns that you could get from an experienced engineer in this forum possibly. If you can afford it, there are single board solutions, VXI and even PXI solutions. It all depends on your time frame and what your NRE costs are relative to your purchase costs.
RE: High resolution VCO
RE: High resolution VCO
You could try these, but you could find lower cost if you can have a slower speed.
http://www.aeroflex.com/products/pxi/3010.cfm
http://www.elcom-tech.com/elcom_ads.pdf
RE: High resolution VCO
If you want to set the vco to a SPECIFIC frequency from pre-knowledge of where you want to go, and without the need to use something like a frequency counter to measure it and dither the voltage up/down until frequency is close enough, then you need a closed loop system--a PLL based frequency synthesizer. The closed loop system will NOT drift frequency with time, so once you set it on frequency, it will stay there for the next year.
RE: High resolution VCO
http://www.madelltech.com/AV1485.html
If you are planning on manufacturing hundreds of these "VCO's", I would be glad to design you a low cost solution.
RE: High resolution VCO
This SC will be voltage controlled w/ sensitivity within 40 KHz/mV (some VCO's are capable of that). I'll be adding to this, a VC attenuator (to control the power output). And since my tunability speed requirements are on the order of 500 msec, I don't think I need a PLL. In fact, the feedback loop could easily go through a laptop measuring the voltage reflecting an incident/reflected power from an antenna. I appreciate your comments. thanks
RE: High resolution VCO
1) Put a ferrite isolator between the VCO and the variable attenuator, something like Model No. PE8301, from h
This way the oscillator will be happier for various loads and attenuator settings.
2) I would use a VCO like this one: ZX95-2500 from mini circuits. It is around 90 MHz per volt sensitivity.
http://www.minicircuits.com/oscillat.shtml
3) Put it all in a box to airconditioning currents can not change the temperature of the vco easily.
4) Use a very regulated power supply for the VCO for the +12 Volt power supply. A few 22 uF tantalum capacitors right at the VCO power supply pin would not hurt either.