Hi,

I’ve been having a look at usrp2/host/lib/copiers.cc and the schematics

to

try and work out if the units mean anything.

As far as I can tell the LTC2284 ADC is set up to use the ±1V input

range

and output 14bits as a twos complement.

From the datasheet/the maths I think the ADC is thus giving possible

outputs

of -8192 to 8191 (i.e ~ ± 2^13) where -8192 represents -1V and 8191

represents 1V-0.000122V.

Where I’m confused is with copy_u2_16sc_to_host_32fc the integers are

scaled

to produce floats where -32768 and 32768 (i.e using the full 16bits of

the

storage variable) are mapped to -1.0 and 1.0 respectively. Is there a

reason

for this? I haven’t tried to look at what the FPGA is doing with this

data

yet…

Can I change this to -8192 and 8192 to map the real/imaginary magnitudes

to

voltages. I think by doing this I should be able to use usrp2_fft.py -S

-f

xx and see the same sort of values as I see on a scope?

Thanks,

Tim