Re: [Discuss-gnuradio] Just wondering why?

[Kevin Reid]

On Wed, Nov 1, 2017 at 9:23 PM, Cinaed Simson <address@hidden> wrote:

>> Not a problem for me most of my testing is done with my test set, the RF gain
>> set at 14 dB means I can receive signals down to -115 dBm, I tend to use
>> signals at around -80 dBm so I am far away from the -5 dBm maximum for the rf

No, setting the RX gain to 14 dB means you haven't done your homework.

Take a look at the output of

   hackrf_transfer

Note

  # RX/TX RF amplifier 1=Enable, 0=Disable.

That is, the RF gain is either on or off for both receiving and
transmitting - it's all or nothing - you don't get to choose the level.

This is true about the hardware, but gr-osmosdr, which is being used here according to the original post's screenshot, expresses all gain stage settings in dB. The RF amplifier is represented as a gain control with a numeric value that can be either 0 or 14 but no other values — it cannot be entered as a boolean through the gr-osmosdr API, and if you try, 1 dB will be rounded to the nearest valid value of 0 dB (amplifier off).

If one is interested in the relevant code, see:

    hackrf_source_c::get_gain_range

    hackrf_source_c::set_gain