Summing of phase noise masks

phase noise measurements I obtained the dBc values, which are

I assume you have phase noise plots for each unit, not just a single number...

Take the dBc/Hz value for each frequency, convert each value to a numerical power value , P =10^(dBc/10), then ADD the powers form enach unit for each frequncy, i.e add all the powers at 10kHz offset for example, then convert each summed power back to dB dB =

10*log(P). You have to add the phase noise power at each frequency for each unit...you can't add dB directly so you have to convert dB to numberical power, ADD, then convert back to dB.

OK?

If you have just a single number at a single offset frequency , you probably don't have enough meaningfull information

Mark

phase noise measurements I obtained the dBc values, which are

By the way, noise is added as squares and then taken the root of it, not just adding the amplitudes.

Rene

phase noise measurements I obtained the dBc values, which are

I beg to differ,,, in the procedure above, we are adding noise POWER numbers which can be added directly. If we were combining noise VOLTAGE numbers, then yes squares/root are needed. But since the numbers are already POWERS, direct simple addition is correct.

Mark

character.>Fromphasenoisemeasurements I obtained the dBc values, which are

Thank you for your ideas!

But I am not sure if your method is mathematically correct. A frequency shifter like the L-band converter uses a mixer. Mixer are mathematically represented by a multiplier. Hence two time signals are multiplied, which corresponds to a convolution in the frequency domain. So if I have two signals with the measured phase noise, my approach would be the convolve these two signals to obtain the entire phase noise. As you described the convolution has to be performed with non dB values.

I tried both method in Matlab, and observed only slight differences in the result. The convolution gave a more smoothed result, but in average the results mainly the same.

Many thanks again for your ideas!

Koxe

character.>Fromphasenoisemeasurements I obtained the dBc values, which are

what you say above is true but the end result is that the mixer simply takes whatever phase noise is present on the LO signal and "adds" it onto the converted signal. Adds means using the method described. Another way to think about it is....phase noise is unwanted FM modulation with noise as the modulating singal.... Whatever FM is present on the LO will also be imparted onto the converted signal. If the LO shifts up by 10 Hz, the converted signal will also shift (up or down) by 10 Hz.

Mark