Hello,
I have been looking at the PXA with NFE to measure very low noise like signal. My understanding is as follow:
- according to datasheet if I want to measure a signal of about -172dBm/Hz at 2GHz, connecting the signal directly to the PXA and without PreAmp nor NFE I will not be able to see this level but I will see about -153dBm/Hz. Using the PreAmp I gain about 10dB so I can read about -165dBm/Hz, and adding on top of that NFE I can reach -172dBm/Hz
- now if I use an LNA in my Rx path to raise the -172dBm/Hz signal to about -140dBm/Hz (thus well above the DANL of -153dBm/Hz) at PXA input I can make the measurement without the use of PreAmp and NFE.
Is this correct? Then I don't see what is the use of the NFE. I can just go down to the same level of measurement using an LNA?
Also what happens if I use the NFE after the LNA 30dB gain? Is the NFE going to reduce the level I read on the display by 10dB whatever the signal input power is or is it intelligent enough to understand that there is no contribution from the PXA?
Many Thanks for your reply
I have been looking at the PXA with NFE to measure very low noise like signal. My understanding is as follow:
- according to datasheet if I want to measure a signal of about -172dBm/Hz at 2GHz, connecting the signal directly to the PXA and without PreAmp nor NFE I will not be able to see this level but I will see about -153dBm/Hz. Using the PreAmp I gain about 10dB so I can read about -165dBm/Hz, and adding on top of that NFE I can reach -172dBm/Hz
- now if I use an LNA in my Rx path to raise the -172dBm/Hz signal to about -140dBm/Hz (thus well above the DANL of -153dBm/Hz) at PXA input I can make the measurement without the use of PreAmp and NFE.
Is this correct? Then I don't see what is the use of the NFE. I can just go down to the same level of measurement using an LNA?
Also what happens if I use the NFE after the LNA 30dB gain? Is the NFE going to reduce the level I read on the display by 10dB whatever the signal input power is or is it intelligent enough to understand that there is no contribution from the PXA?
Many Thanks for your reply
Noise Floor Extensions (NFE) is a software-based technique that effectively reduces the level of noise for spectrum measurements including CW power, band power, adjacent channel power, and pulsed-RF characterization. The noise reduction is not as universally useful as true improvement of noise figure in a spectrum analyzer, but can often be remarkably effective. Its effectiveness is modest with CW signals, and excellent with noise-like digital-communications signals, and often also excellent with pulsed-RF signals.
Dynamic range is a core measure of spectrum analyzer performance, and can significantly affect other core measures such as accuracy and measurement speed. Spectrum analyzers have many different measures of dynamic range, and most of these include noise, specifically the analyzer’s own internally-generated noise. Reducing the effective analyzer noise floor therefore improves dynamic range and the quality of many measurements. While lowering an analyzer’s inherent noise floor through hardware design and component choices is obviously beneficial for dynamic range, there are practical limits, and another approach offers significant improvement. With sufficient processing and other technical innovations, the noise floor in signal analyzers can be modeled and subtracted from highly averaged signals to reduce the effective noise level. In the new Agilent PXA signal analyzer this operation is called noise floor extension (NFE).
The first step in subtracting the noise contributed by the analyzer is to accurately characterize it over the operating range of the measurements. This involves modeling the noise floor and combining the model with measurements of individual analyzers to accurately estimate their noise floor. The noise of the analyzer adds incoherently to the noise or any other signal type that constitutes the signal to be measured at the analyzer input. Therefore the predicted input power is simply the observed power of the signal input plus noise, minus the observed noise power. Please refer to Agilent Application Note 1303 (Literature number 5966-4008E), “Spectrum Analyzer Measurements and Noise.” Also, please refer to the NFE application note: http://cp.literature.agilent.com/litweb/pdf/5990-5340EN.pdf
When using a Low Noise Amplifier (LNA), you can use the same basic principles of noise cancellation. You can first measure the noise of the LNA with the input terminated, and can then hold this trace on the PXA. You can then measure a signal that is connected into the LNA with the PXA. You can then use trace math to subtract the trace holding the noise power from the trace with the input signal to the LNA connected.
Simply connecting the LNA to the analyzer, would result in noise reading that is the combination of the LNA’s noise contribution plus its gain. Turning on and off NFE would not affect this result if the LNA’s noise contribution is sufficiently higher (>10 dB) than the analyzer’s noise floor without NFE turned on. So, the results you are getting are to be expected, since the LNA’s noise figure + gain appear to be about 34 dB, which would yield a reading of about -140 dBm/Hz
Regards -