ad9850 DDS module power output, wheat stone, max power, measurable impedance

Discussion in 'The Projects Forum' started by ninjaman, Oct 31, 2014.

  1. ninjaman

    Thread Starter Member

    May 18, 2013

    I have a ad9850 DDS module from ebay, a wheat stone bridge with 50 ohm resistors and an unknown impedance. the DDS puts out 350mV rms (I think this is at 7MHz) from a source impedance of 100 ohms. this it going into the unknown impedance. im guessing that because the unknown impedance is the load and includes the wheat stone bridge resistors, and the unknown load could vary. it wouldn't be 100 ohms, meaning max power transfer isn't happening? is this right or am I completely lost on that.

    DDS, 350mV, 100 ohm========Load, unknown (from 5 to 2000 ohms)

    I have a technical spec from a sark 100 analyser. it says it can measure from 5 ohms to 2000 ohms. is this range found by using the output power, the 2000 ohm impedance and the power of the reflected wave. im guessing its a case of not enough power back from the 2000 ohm impedance and that is what limits the meter? im not sure how to find the output power of the DDS.

    any hints would be good. I have looked at the data sheet
    I don't know if the low power 380mW or 155mW is the output. and im not sure if that would drop or rise at the 30MHz range. I think the 350mV is at 7MHz.
    would the output power stay the same?
    further reading and the 155mW is the power dissipation not the output.

    this output power will go through a wheat stone bridge of 50 ohms to an unknown impedance. the reflected wave will go through a peak detector, buffer amp with a gain of 9 to be measured by the microcontroller.
  2. crutschow


    Mar 14, 2008
    I'm rather confused by you post. :confused: The AD9850 DAC has a high-impedance current output so I don't know what 100 ohm source impedance you are referring to.(?)
  3. ninjaman

    Thread Starter Member

    May 18, 2013
    I got it from

    I looked at the data sheet and the output impedance says from 50 (min) to 120 (max) kohm.
    I took the 100 ohm impedance because I think that is from the DDS module and not the chip itself. could the source impedance be changed by the components on the module?