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LMX2492EVM: Continuous Sawtooth Ramp

kacem ekki
Prodigy 10 points
Part Number: LMX2492EVM
Other Parts Discussed in Thread: LMX2492,

Hi everyone!

Now i am testing the LMX2492 EVM. I downloaded and installed the current version of TICS Pro

I followed all the instructions on LMX2492EVM  User's guide.

Then I tried the example provided on page 8 Continuous Sawtooth Ramp (9600 to 9700 Mhz). But I get always a weak signal in RFout/2 (≅-65dbm) with 20dbm attenuator.

The signal i got on spectrum analyzer is attached. Screenshots of other configurations are also provided.

Is there anything else i forgot to do?

Thanks

  • 0
    TI__Guru* 98190 points

    Hi Kacem,

    Your Vtune voltage looks normal, would that be a spectrum analyzer issue?

    If you do not ramp, can you lock it to 9600MHz and 9700MHz?

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Thank you for your response I lock to 9600MHz and 9700MHz, and I got the result below:

    But when I switch to continious sawtooth ramp I get the same weak signal

  • 0 in reply to kacem ekki
    TI__Guru* 98190 points

    Hi Kacem,

    the measured power is very small even if it is not ramping. Could you check your spectrum analyzer configuration again?

    If you use spectrum analyzer to capture the ramping, you should use max. hold. 

  • 0 in reply to Noel Fung
    Prodigy 10 points

    I retested without 20db attenuator:

  • 0 in reply to Noel Fung
    Prodigy 10 points

    But When ramping, the signal is still weak 

  • 0 in reply to kacem ekki
    TI__Guru* 98190 points

    Hi Kacem,

    I strongly believe it is a spectrum analyzer issue, probably due to improper RBW setting, your sweep time is also too long. Do you have test equipment that can measure freq vs time?

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Indeed you are right I have a doubt to the sweep time, here is the technical characteristics of the spectrum analyzer: 

     I retested with another spectrum analyzer which gave me -5dbm in RFOUT for (9.6GHZ, 9.7GHZ and ramp 9.6 to9.7GHZ) while it gave -9 dbm in RFOUT/2 for the same frequencies it looks like enhanced since the power outout is stable but the doubts still exist since I have a limitation in sweep time to 10ms however the ramp duration is 100us.

    which output power I have to reach with this EVM in RFOUT and RFOUT/2. can you send me an example of a continious sawtooth ramp with the same EVM, otherwise, an Excel table which contains the measure power of several single frequencies and ramps 

  • 0 in reply to kacem ekki
    TI__Guru* 98190 points

    Hi Kacem,

    Looks like you are not using a standard spectrum analyzer, if the IF BW in the spec = RBW, you are not able to change it to a higher value and reduce the sweep time. 

    From Figure 6 in the EVM user's guide, output power at 4.8GHz (div/2) output is -3dBm.