Optimal / maximum RF input level

I am not sure if there is an easy answer to this question, but what is the optimal maximum RF input level? Obviously you don't want A/D overload and clipping, but should the signal level be kept even lower than that, perhaps to avoid any nonlinear regions of the front end amp?


  • edited March 2019
    that's a little tricky because you have to consider the sum of all the big signals in the HF range, not just what you see. I use S9+40 dBm as my goal when filtering, notching or nulling the biggies.
  • Right, let's assume I can put an accurate scope on the RF input. What's the largest acceptable peak value? Or even better, what's the maximum A/D count? (With a way to view it on the Admin panel)
  • From here: http://kiwisdr.com/quickstart/index.html#id-overload
    Tests with a signal generator show the ADC overflows when a single-tone exceeding -15 dBm (almost S9+60) appears on the antenna terminals.

    -15dBm at 50 Ohm would be 56mV peak.
  • From the LTC2248 data sheet, "Connecting SENSE to VCM selects the internal reference and a ±0.5V input range. " which according to the schematic is what R408 does.
    20 dB of LTC6401 gain, data sheet again, and 2 dB of LPF loss, an estimate, would produce 18 dB gain ahead of the conversion. This net gain would turn a sine wave of 44.5 mV rms ( -14 dBm in 50 ohms) at the SMA connector into 1 V p-p at the LTC2248 ADC. I'm guessing that the OV indicator comes on when the instantaneous input exceeds this level, which agrees closely with what we all measure.
Sign In or Register to comment.