Testing an RF oscillator

[Coust]

Hello everybody!

I need advice to find the best way to test my Rf oscillator. At the beginning I used this oscilloscope Agilent InfiniiVision 5000/6000/7000 Series Oscilloscopes with 10073C probes. The problem I found was that the parasitic capacitance of my probes modify the osicllator frequency so, to fix that, I built a buffer to isolate the tank part of the oscillator from the probe's part. With the buffer I hope that the parasite capacitance doesn't affect the frequency of operation but I don't know if I have solved the other problems.
My teacher recommended me to use SMA connectors and SMA cables to improve the signal but I found that those cables have a parasitic capacitance of 100pF/m (I have a 0.5m one) and when I introduce them in my simulation, I get the signal attenuated. The question is: Do I need another way to mesure the oscillator or just another SMA cable with low capacitance? What is the regular procediment to measure this kind of circuits?

The circuit here:


Ty very much!

 

[Ow@i$]

whats your oscillation frequency?
yeah the probe does effect your measuring e.g. a probe of 10MHz will surely give different result then a probe of 1GHz when used for testing a 1GHz application circuit.

 

[Coust]

My oscillation frequency is 868MHz. Yes, I noticed this before I built the buffer. The question is: How do I test it now? Should I connect the SMA cable directly at oscilloscope? Is there any common way to measure those Rf circuits?

Ty very much for your advice!

 

[Ow@i$]

the thing with RF is one need to have proper instrument to conclude a result. Sorry I don't get when you say connecting SMA cable directly to scope?? you mean from the output of the oscillator through a SMA connector and cable you will connect it to the scope???

Perhaps for a test it just came in my mind, try reverse configuration of cable for measuring!! I mean connect the probe (Needle part) of the cable with ground and the ground part(crocodile clip) at your measuring point.... I assume a slight difference would be there in your result ?? give it a try!!

 

[Coust]

Yes, when I say "connecting SMA cable directly to scope" I mean connecting a SMA cable from SMA connector to oscilloscope. I think that in this way I would avoid the parasite capacitance of the probe but not the one from the cable.