Spectrum Vs. Network analyser - for frequancy response measure

[levnu]

if i would like to measure a frequancy response of one of my RF circuits should i use Spectrum or Network analyser?

i would like to measure different output voltages under different input to my circuit freqs

are there any advices how to do it right ? becuase i never used such before

Thanks

 

[albbg]

You have many options:

1. Use a spectrum analyzer with integrated tracking generator
The generator is inside the spectrum; the generated and measured frequency will be the same and will be automatically swept in the range you specified.
2. use a couple generator+spectrum analyzer.
In this case, if you want to observe the behaviour over a certain band you need to set the generator in order to sweep the band automatically, or you have to change mnually the frequency. The spectrum have to be set in order to display the whole band. In case of generator set to sweep the frequency band you should set the spectrum as "max hold", otherwise you will see a peak passing through the screen.
3. Use a network analyzer
For this simple task the behaviour is similar to that of spectrum+tracking.

In all the cases the bench will be calibrated in order to eliminate the contribution of the cable. Furthemore amplitude will be set to comply with expected value+some margin. Be careful not to exceed the maximum input power of the instrument.

 

[Borber]

Fourth possibility is to use proper noise generator and spectrum analyser. It will show circuit frequency response.

 

[levnu]

Thanks,
attached the circuit ilustration that theoreticly i would like to measure its freq response,
its an inductive coupled circuit that i would like to measure its freq response while drawing different loads from the secondary. i think that the primary is driven by some Half or full bridge though and not like in the ilustraion.

conseptualy questions:

Thanks again
1. can i only measure the resonance of the secondary by it self if yes how? becuase it will be passive without any power
2. can i measure while primary and secondary are coupled? if yes where should i measure to have the whole system response? in what point on the circuit
3. should i do it when i change K factor, for understanding the response?

4. do you think that if i measure the system while drawing current from the secondary any destractive power can drift to the spectrum analyser?

5. does spectrums can deal with more power than networks?

 

[FvM]

Regarding question 1 to 3: All circuit elements are acting together, there's no thing like a "secondary resonance". You can either measure individual circuit elemnts while isolating, shorting, disconnecting etc. others, or measure the overall properties of the complete circuit

It should be noticed, that a vector network analyzer measuring complex S11, S21, S22 gives a multiple of the information a scalar transmision function can ever reveal.

Both network analyzer and spectrum analyzer have strict "external" power limits that must be observed. Measurements at a power electronic circuit in operation don't seem to make much sense as far as a characterisation of the LC circuit is intended.

By the way, the initial post is talking about RF circuits. Apparently the problem has changed somehow.

 

[levnu]

i always thought that the circuit (inductive coupling) above is sort of an RF circuit, am i wrong?

if i want to define well the circuit (as a whole system) where should i measure the freq response?
each part alone or when the circuits are coupled? where should i measure? where to place the prob? on the primary coil? should it be under different secondary circuit loads? and under different k factors? what will help me to define as best as possible the inductive coupled system? by using this measurent instruments?

 

[FvM]

For low and medium frequency circuits (e.g. below 1 MHz), I would measure the coupled inductor parameters with a LCR meter and calculate the overall circuit beahviour.

Non-linear behaviour is a special point. It would be usually accessed by operating the circuit regularly and observing voltages and currents.

 

[levnu]

thanks, so what you are saying is that measuring the system with spectrum analyzer won't help me to define the coupled system? because it has non liner behaviour... but won't it show me the freq response under each load?
the LCR meter params are not helping me becasue there are many other parameters that are around for i.e. metal above the secondary etc. it also influence on the voltages and currents and i'm looking for some complete and observative solution that will help me to define the response of the coupled system under any of its physical conditions

from your answer it seems that i can't achive that ...... :-(

i thought i would be able to give some general definition to the coupled system by using the spectrum absorvation parameters, such as res freq, gain, changes of the resonance under loads, different k factor, load modulation influence on freq response etc.

 

[Borber]

For abstract problem you should use abstract instrument. Just imagine whatever you want.