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Old 26th Nov 2022, 12:42 am   #272
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: 6-gang FM stereo tuner heads

I have just done a "filthy" TOI test of the SSA3021X+ without DUT like what it is described in the RS white paper. I dont have the LP filters for the 10MHz and 10.1MHz tones so I stick two 20 db attenuators to isolate two signal sources further. The 2nd harmonics for the FY6900 are to be -67dBC, and DG1022Z to be -51.65dBc at 10MHz fundamental.

I have tested the mixer of the SSA3021X, setting the built-in attenuation 30db, 20db, 10db and 0db at 10Hz RBW (10 sample averaging). The pre-amp is turned off in all cases except in the last attachment with 30db attenuator.

My two tones are not exactly the same level and you can see the TOI is higher with higher input level at the upper side. The results are very similar for attenuation from 30db to 10db. Only at 0db attenuation, the TOI degrades drastically. Strangely enough the pre-amp does not degrade the TOP with 30db attenuation( attachment 5).

I can try to repeat the test by making two LP filters for the frequency sources. I am trying to understand what is going on here and what are the limitations of the spectrum analyzer rather than treating it as a black box.

According to Siglent, the TOI is > 14db at 1GHz, with -20dbm two-tone, 0db atten, RBW=10khz.

I think there are mistakes in the RS white paper mentioned in my last post about the 3rd order IMD products at f1-delta _f and f1+delta_f.. But how could it be? They are the experts and not me. I struggle with the idea that when you have two phase uncorrelated sources enter the mixer, somehow there will be constructive and destructive interference. I can easily understand it in time domain when two tones of different frequencies can have constructive and destructive interference along the nodes, but I cannot visualize the same in the mixer within the frequency domain.
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