harmoics meas setup questions.....

I am trying to understand the meas setup as attached here:

PA(24dBm output)->6dB attn.->High pass filter->Spectrum analyzer

Questions are:

1. Why do I need to use the 6dB attn?
2. what is the purpose of the high pass filter?

Thanks in advance

MK28

highpass filter attenuates the fundamental power but lets the harmonics thru unattenuated. You get a more accurate measurement that way, since harmonics generated in the spectrum analyzer itself are minimized. You need th pad to keep the amplifier thinking it has a matched load.

Thanks biff44!

Usually HP input impedence is 50 ohm, so 50 ohm load is seen from PA output, correct? so load impedence seeing from PA is 50 ohm, but PA output impedence is higher (I assume!)...therfore, due to this impedence mismatch there will be some power reflected back, correct? But having attenuator lowers this mismatch!

Is my above statement correct?

It should improve the VSWR between PA and filter.