[USRP-users] Questions on set_rx_gain

James Humphries james.humphries at ettus.com
Mon Mar 7 10:00:56 EST 2016


Hi Maurizio,

It really depends on the application as to what you set the gain to. What
kind of input power do you expect on the RX? Is this for a B200/210, if so,
a good starting point is around 20-30dB.

Here is some data I took a while back (see attached photo). The lines end
where I started to see distortion with too much input power. Maybe this
will help as a rough guide. Note the high noise floor at 0dB gain, you need
some gain to improve the noise figure.

-Trip


​

On Mon, Mar 7, 2016 at 8:32 AM, Maurizio Crozzoli via USRP-users <
usrp-users at lists.ettus.com> wrote:

> Martin Braun via USRP-users <usrp-users at ...> writes:
>
> >
> > That is correct; an analog gain is applied. Note it is still possible to
> > "do damage" this way, e.g. by driving amps or ADC into saturation.
> >
>
> So what's the rule?
> Setting the correct gain seems to be really critical but I cannot
> understand
> what is the correct approach to decide a reasonable value: is it just a
> cut&try approach?
>
> AGC might help from a theoretical point of view. But just theoretical, I'm
> afraid, as far as I have understood, because most likely you tend to get
> damages when AGC is on.
>
> Nevertheless AGC would be really needed when your signal level fluctuates
> along a wide range of values. And if the best suggestion is to avoid AGC,
> we
> go back to the initial questions.
>
> Comments, suggestions, even tutorial from a practical point of view are
> more
> than welcome (they might even be worth of becoming a FAQ for SDR
> not-so-experienced users). Volunteers?
>
> TIA!
>
> Maurizio.
>
>
> _______________________________________________
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>
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