Re: [Discuss-gnuradio] window sizing issue

[ematlis]

Ok, I can accept that this device was not intended to be used as a 
calibrated measurement device, but maybe I can give it a shot.  If I keep 
the decimation constant, and stabilize the temperature, what other 
considerations do I need to take into account (other than the obvious one, 
ie gain) for the basic am-demodulation routine I am using?  Can I consider 
the FPGA as a "black box" and just calibrate the output vs the input at 
the physical connector?

thanks,
eric

On Fri, 16 Mar 2007, Eric Blossom wrote:

> On Fri, Mar 16, 2007 at 05:30:44PM -0400, address@hidden wrote:
> > Thanks-
> >
> > I'm using the DC-30 MHz basic RX board.  So by recording the input signal,
> > recording the value displayed on my "time series" window, and knowing the
> > gain (0-20db if memory serves) I can calibrate the hardware so that I can
> > back out the original voltage levels at the input?  What impact does the
> > signal processing have on the absolute magnitudes?  If there is some
> > magnitude attenuation caused by the FIR filters, is it frequency
> > independent?
> >
> > thanks,
> > eric
>
> Not to discourage you, but the USRP was designed as a software radio
> peripheral, not a precision calibrated measurement device.
>
> You will have to calibrate _everything_ in the path, and of course
> that includes the signal processing in the FPGA as well as anything in
> the host-based signal processing path.  And yes, pretty much all of
> this varies depending on a large variety of settings.  E.g., you'd
> want to calibrate for each possible FPGA decimation rate that you're
> interested in.
>
> Also, any calibration you make is going to be temperature dependent.
>
> Eric