Frequency accuracy of PPM

[Hubert Dong]

Hi, I have a question for PPM.
The resolution of PPM is 0.1nT, so the resolution of frequency is 0.1/23.4874= 0.0042576 Hz.(If for Overhauser Magnetometer is: 0.01/23.4874=0.00042576Hz )
The signal of PPM is very noise, How to do for this high accuracy measurement of frequency ?
Regards,

[Willy Bayot]

Hi, I have a question for PPM.
The resolution of PPM is 0.1nT, so the resolution of frequency is 0.1/23.4874= 0.0042576 Hz.(If for Overhauser Magnetometer is: 0.01/23.4874=0.00042576Hz )
The signal of PPM is very noise, How to do for this high accuracy measurement of frequency ?
Regards,

Even if you aim at a resolution of 1nT which is enough for most practical site survey applications, you still need to measure the precession frequency with a resolution of 0.04Hz.
The first problem is to amplify the decaying sine wave of around 1µV peak-to-peak sufficiently to digitally convert it without amplifying the noise. Thus, you need to tune the sensor to the approximate local precession frequency. This brings a good bandwidth filtering and amplification.
Then, you need a stage of low noise pre-amplification before the main amplifier and the ADC stage.
Then comes the difficulty to measure the frequency with enough accuracy in spite of the residual noise and, more importantly, potential spikes.

YES, it is a difficult task to design and build a decent PPM.

Look at http://users.skynet.be/fa352591/index.htm


Willy

[Hubert Dong]

How to build a low noise pre-amplifier ?
If the field is unknow, the tuning capacitor will be variety according to the field. what it is algorithm for capacitor finding?

[Boattow]

Look here

These 2 websites answer all your questions...

http://perso.infonie.be/j.g.delannoy...Guidelines.htm

http://www.gellerlabs.com/PMAGThoughts.htm