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LMX2594EVM: lmx2594evm and sv601349 board

Jeffrey Pawlan
Prodigy 60 points
Part Number: LMX2594EVM
Other Parts Discussed in Thread: USB2ANY, LMX2594

I am measuring huge amounts of noise and spurs in the sidebands of a CW signal generated by the LMX2594EVM while I am connecting it with the Reference Pro board (SV601349).  I have tried several frequencies including the supplied default of 7GHz and also 11.7GHz which is what I ultimately want.

1.  I located the source of most of the noise. It is coming from the Reference Pro board (SV601349) board. When I place a piece of ferrite on top of the IC the noise is reduced by more than 20dB. What is causing this on the reference Pro board?

2.  I then substituted an older interface supplied with with a different EVM. It is the USB2ANY module.  It loads the LMX2594EVM correctly from TICS and has far lower noise.  However, now there are a few large spur signals in the sidebands of the microwave signal from the LMX2594EVM.  One is at 2.5KHz away from the carrier and is only 20dB down from the carrier level.  What is causing this?

  • 0
    TI__Mastermind 28960 points

    Hi Jeffrey,

    Are you powering the Reference PRO through USB? It's possible the USB power supply is not very clean, and this is contaminating the LMK oscillator on the Reference PRO. You can try using the VccEXT connector and jumpers to eliminate USB power supply noise. You could also try inserting a self-powered hub between the USB2ANY or the Reference PRO and the USB connection to the PC, as this would likely have a self-contained and much cleaner power supply.

    Regards,

    Derek Payne

  • 0 in reply to Derek Payne
    Prodigy 60 points

    I had already known to unplug the USB cable so there was no power going to the interface board. I can even disconnect the ribbon cable because the synthesizer registers are already loaded.

    This morning the large sideband was not there but I am now using a different frequency so perhaps it was generated my my signal generator which I use to mix the microwave signal down to 100MHz to read more accurately on my spectrum analyzer.

  • 0 in reply to Jeffrey Pawlan
    TI__Mastermind 28960 points

    Signal generator noise is plausible. It sounds like your setup is slightly more complex than I envisioned, so could you tell me how everything is connected? So far I've heard there is a Reference PRO generating the input reference (at what frequency?), or alternately some other reference when using USB2ANY (?); a lower-frequency spectrum analyzer, or else a spectrum analyzer with higher accuracy at lower frequency range; and some external signal generator mixing down the output of LMX2594 to 100MHz.