AD831 down mixing into Audio range


I currently use a CN PCB with 9V supply and would like to use 2 closed freq. mixed into audio range.

1. Freq. 10Mhz

2. Freq. 10Mhz + 100...50kHz

Currently added the filter caps as 10nF (may change later lower for may 200kHz).

The questions are now, how to configer 10Hz...100kHz mixer regarding:

. the 5K/5K & 0.1 uF Cap network for the  VFB

. clear sine output (not clipped) in that range as low THD

. constant LO input level as mentioned as-10dBm, but level for the full range as 10Hz...100kHz

. The output caps may altered to for this 10Hz...100kHz range

. whether the 9V topological to use or +/- 5V

While currently my results using 10nF filter caps:

. OK down mixed at 9kHz diff

. 400Hz LO have to go down to 5mVpp to get clear sine !!??

So the question is how to configure & drive a down mixer into the 10Hz...100kHz range without any THD!

While the MCL mixer have no filter options, so the AD831 is IMHO a good match.

  • Well, no any Analog Device engineer's on sky yet O:(

    Now tested the +9V single powering some more...

    1. I set the LO level, so that the limiter does not work anymore or do not need to work any more. About 100..200mVpp

    2. Measured the output at the IFP, so no output driver involved, to get into the real behavior.

    3. the RF is still about 10dBm at 10MHz

    4. changed the LO freq to 10.020MHz, 10.010MHz, so output is OK

    5. Changed as on 4) LO freq below 10.005...10.0004, output level continues rises as lower the freq. difference gets.

    6. In other words... WHY rises the output level f(freq) as below 5...6kHz difference!!!  Data spec's defines down to DC!!

    Spec sheet erratas revision D:

    1) at page 8 "Using the Output Amplifier" >> 50 Ohms load, false is 50 V load

    2) at page 11 Figure 10 at the right as output >> IF Output, false is RF Input

    So engineer please...