about ADRF6820


1. What is the function of  "PWRDWN" switch on evaluation board?? No matter "PWRDWN" is pull high or pull low, ADRF6820 still working.

2. When using internal LO,

    RFIN : 1900MHz, 0dBm, CW tone

    REFIN : 153.6MHz, 0dBm, CW tone

    LO set to 1890MHz (using customer evaluation software)

    => I+ port (we remove transformer T6 and resistors R38 & R42) see a ~38MHz ~358mVpp sinewave (oscilloscope is set to 1Mohm)..

    When using external LO,

    RFIN : same as above setting

    LOIP : 1890MHz, 0dBm, CW tone

    => I+ port see a ~10MHz ~273mVpp sinewave (oscilloscope is set to 1Mohm).

    Our question are:

    a. When using internal LO, why the IQ sinewave frequency is not ~10MHz??

    b. Why the amplitude level of I+ signal has large difference between using internal LO and external LO??

    c. For external LO case, do you have a formula to calculate the I+ Vpp value with RF input power level??