broadband noise measurements - RF Cafe Forums

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cubeleg
 Post subject: broadband noise measurements
Posted: Thu Oct 04, 2007 1:18 pm 
 
Captain
User avatar

Joined: Tue Dec 05, 2006 1:55 pm

Posts: 5

Hi!

I want to ask a question, please I'm newbye in microwave and RF thecniques, so please, feel free to close the thread if it is just a stupid question.

I am trying to measure noise of resistive elements in the GHz range. We are looking for new devices based on ferromagnetic materials, then the ferromagnetic resonance is an important noise source.

In first place I am not sure about the equipment needed in order to perform such a task. I can imagine that a broadband (about 0.1-20GHz) low noise amplifier and a spectrum analyzer are needed, also a low loss line is recommended in order to reduce the noise introduced by the line. It is needed anything else?

Secondly, is there any book which would help me in this task, I have read pozar's book: microwave and RF design of wireless systems, and search in forums information related with it.

Regards

Rubén
 
   
 
cubeleg
 Post subject: more questions
Posted: Tue Nov 13, 2007 6:36 am 
 
Captain
User avatar

Joined: Tue Dec 05, 2006 1:55 pm

Posts: 5

Hi all!

I have begun to do the test on the system, I have just get an spectrum analyzer and a amplifier. Unfortunately I don't have a noise source, but I have tried to measure de noise generated by a 50ohms terminator placed in the input of the amplifier. The noise figure of this device in unknow, I have estimated the gain by measuring different synusoidal frequencies and it is about 140 with a bandwith of 1GHz. The preamplifer of the spectrum analyzer has a NF of 11dB.

The problem is that I am obtaining less espectral density than the expected in input (about 805pV/sqrt Hz, while 50ohms have to have about 900pV/sqrt Hz). I have check that the gain compression begins at 1mVrms in the input, so I am far away from compression region which could explain such a low espectral density value. I also check the amplifier with a vector network analyzer and it has a reflection in the input of about -0.2 at 700MHz, could this be related with the obtained reduced noise values? suggestions or ideas :?: ?

Cubeleg

Posted  11/12/2012