Re: [Discuss-gnuradio] USRP receiver filter response

[Johnathan Corgan]

On Wed, Sep 24, 2008 at 7:53 AM, Kell, Scott <address@hidden> wrote:

> I put a 9dBm tone in at 50 kHz

What gain do you have set for the receive side?  For the BasicRX or
LFRX, this is really the gain of the input driver to the ADC, which
can vary from 0 to 20 db, and effectively changes the full scale ADC
range from 2V p-p to 0.2V p-p.  Your input of 9dBm at 50 ohms is 1.78V
p-p, so, depending on the gain setting, you might be clipping.  It's
not clear how you are measuring your output, but if you are using
usrp_fft.py and not specifying a gain, then it takes the mid-point,
which would set full scale ADC at 0.63V p-p.

With clipping, at some frequencies you will generate harmonics which
will fall into the passband of the CIC filter and throw off your
calculations (assuming I understand how you are sweeping and
measuring.)

-- 
Johnathan Corgan
Corgan Enterprises LLC
http://corganenterprises.com/