Wire format: using 8-bit (sc8) vs using 16-bit (sc16) resolution to gnu radio

Hi, i am using usrp N200 and i set to gnu radio the wire format as
either
16-bit -> sc16
or 8-bit ->sc8 and host format fc32(complex float) when i use
a) sc16 the power in the window where i see the spectrum is at -110 dB
or
-100 dB, without transmitter sending data (so i see only noise)
b) sc8 the power in the window where i see the spectrum is at -80 db,
without transmitter sending data (so i see only noise as before)

Any ideas why i have a bigger starting power in 8-bit? It is -80 dB
again
-110 dB.

Thanks

On 29.05.2015 12:53, Nick Kara wrote:

Hi, i am using usrp N200 and i set to gnu radio the wire format as
either 16-bit -> sc16
or 8-bit ->sc8 and host format fc32(complex float) when i use
a) sc16 the power in the window where i see the spectrum is at -110 dB
or -100 dB, without transmitter sending data (so i see only noise)
b) sc8 the power in the window where i see the spectrum is at -80 db,
without transmitter sending data (so i see only noise as before)

Any ideas why i have a bigger starting power in 8-bit? It is -80 dB
again -110 dB.

Hey Nick,

it’s all kind of arbitrarily scaled anyway (meaning that the absolute
value, 80 vs 110 is not very meaningful). So this is just an artifact of
how ADC bits are mapped onto the sc8 bits, and then the scaling. It does
not mean you’re receiving more power or anything like that.

M

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