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Too easy ADC overload - will be hardware fix in the future?

LacekHUNLacekHUN
in KiwiSDR Discussion
Now my Kiwi works perfectly. The ONLY issue is the ADC overload above -30 dBm.
At evening a lot of stations on 49 and 41 meterband booming in and reaches -20...15 dBm at their peaks. Especially CRI and TRT. They makes terrible overloading in the whole spectrum.
I cannot build notches to all problematic frequency :)

Is there any HW improvement in the future, that allows Kiwi to handle high signal levels, like -15 dBm?

Comments

  • BjarneBjarne
    What the KiwiSDR doesn't have, but most other SDRs and receivers do have, is an attenuator. I understand that these are relatively easy to make, and be placed in the antenna feedline. I found a couple fixed value attenutators during an internet search, such as http://www.ve6kq.com/dx440attenuator.pdf. I'm sure with the correct potentiometer, a variable attenuator could be made too.

    Bjarne Mjelde
    arcticdx.blogspot.com
  • jksjks
    edited April 2017
    Well, it sounds like you don't need to be building notches but rather putting a 10 - 20 dB attenuator on the antenna input. Or even using a smaller antenna.

    There is no switchable attenuator on the Kiwi because to do it properly, in our opinion, it really needs to be done mechanically (i.e. relays). And that is very expensive. Just Google around and you will find stories about other SDRs in the Kiwi price class with electronic attenuators that suffer from terrible distortion products. Distortion caused by the same high-level signals they are trying to attenuate. This is a very well known problem.

    The Kiwi gives you a 14-bit ADC and a medium-sized FPGA at a relatively low price compared to similar devices. In exchange you need to operate it within its limitations. So that means accounting for input dynamic range: protecting against high-level signals AND spending the time to improve your local noise floor.

    So, no, there will be no front-end hardware changes to the Kiwi because, in our opinion, there's nothing wrong with it.


  • G8JNJG8JNJ
    Hi Laszlo,

    It's still possible to add wider notch filters or band-stop filters as required. 

    They just become more complicated to make and set up correctly.

    I've attached plots of one example I quickly designed using ELSIE (free).


    Choose a shunt or series input band-stop filter and put in the center frequency, bandwidth and terminating impedance, then adjust the values to suit. 

    Drop me an email if you need help.

    Regards,

    Martin - G8JNJ






    Attachments:
    https://forum.kiwisdr.com/uploads/Uploader/64/052f787d9bf97806f8e9dcb75c7da8.png
  • WA2ZKDWA2ZKD
    edited April 2017
    martein.home.xs4all.nl/pa3ake/hmode/bpf_notch.html
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