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Re: [Discuss-gnuradio] window sizing issue

From: ematlis
Subject: Re: [Discuss-gnuradio] window sizing issue
Date: Fri, 16 Mar 2007 18:29:42 -0400 (EDT)

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?


On Fri, 16 Mar 2007, Eric Blossom wrote:

On Fri, Mar 16, 2007 at 05:30:44PM -0400, address@hidden wrote:

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


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.


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