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Strange steps in band (GC5016)

Ondrej Karas13780
Prodigy 210 points


Hi,

I tried to create 4 independent channels with 5MHz bandwith, continuously behind. (Center at 85, 90, 95, 100MHz) on TSW4100. It works, but On the spectrum analyzer I saw some steps (on attached screen shot). Please could some explain what this steps means? I enclose screen shot of TSW4100 GUI also.

I am using Anritsu spectrum analyzer with trigger generator (0 dBm output power).

Thank you.

Ondrej

  • 0
    TI__Mastermind 37500 points

    Hello,

    The TSW4100 example has 4 Down convert channels from a common ADC, has 4 Up converter channels, a summer and output to a DAC.  If you have input 4 Mhz channels it appears that either the input, or digital repeater has a gain mismatch, or programming problem.

    The ADC is sampling at 160Mhz, the 2nd Nyquist zone is selected, the first step is that the IF frequencies are within the proper Nyquist zone, this appears OK.

    The decimation ratio is a CIC ratio, and a PFIR decimation of 2.  A CIC decimation of  8 indicates the PFIR output or PFIR input rate is 10Msps. 

    The PFIR filter design is set for a 5Mhz passband, with a 1.5db passband ripple.  If you want to have less passband ripple you will have a lower gain variation.  The gain variation would be over 5Mhz, not like the spectrum analyzer output.

    Each BB channel for the DDC output has a gain.  The gain can be varied but this is used for fine tuning.

    On the far right of the display, the interleaved IQ baseband interface has a clk rate, and a Sync Delay.  It is normally the same value for all channels.  I suggest you put in a tone .1Mhz above each IF center frequency, one channel at a time.  Following the TSW4100 user guide for Sync Delay adjustment, adjust each channels Sync delay for the proper output tone .1Mhz above the center frequency.  Repeat this test for each of the 4 tone signals.  When the 4 tone signals work, then retest your 4 channel modulated signal repeater case.

    Fine gain adjustments are usually in -db range, so you may need to adjust from -6 to 0db

    Regards,

    Radio Joe