USRP FLEX900 Daughter Boards Calibration

Dear All:

I need to calibrate my USRP with Flex900 daughter boards to take real
world
measurements in dBm. But I am confused with the gain parameter that is
used
in usrp_fft.py.

  1. Not sure whether the RFX900 board has a PGA of its own
  2. Or is it just the AD9862 PGA before the ADCs
  3. The gain bar/parameter varies over 0-90, what does this represent?
  4. When you increase the gain from 0 till 30 or abouts there is no
    change in
    the noise floor? why is that?

If you have any docs that I can go through to understand the gain
characteristic, please.

Kind regards,

Shabbir

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On Wed, Jul 29, 2009 at 04:29:35AM -0700, Shabbir A. wrote:

Dear All:

I need to calibrate my USRP with Flex900 daughter boards to take real world
measurements in dBm. But I am confused with the gain parameter that is used
in usrp_fft.py.

  1. Not sure whether the RFX900 board has a PGA of its own

The RFX boards have adjustable gain on the Rx side, controlled by
one of the low speed DACs.

  1. Or is it just the AD9862 PGA before the ADCs
  2. The gain bar/parameter varies over 0-90, what does this represent?

Roughly the gain in dB relative to an unspecified point.

  1. When you increase the gain from 0 till 30 or abouts there is no change in
    the noise floor? why is that?

Not sure.

If you have any docs that I can go through to understand the gain
characteristic, please.

The code that controls the two parts of the gain setting can be found in

db_flexrf.cc, flexrf_base_rx::set_gain

You might want to add a couple of printfs to that code to see what’s
going on.

Eric

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