I figured it out. The USRP input must have an input amplitude between 0 and 32767. When the amplitude was low the signal power was below noise so I couldn't see anything in the FFT. When I raised it to 20000 I was able to see the peak around ( signal frequency +/- offset ).
Marcus about your statements about the SAW filter; I will know a little more about it first from the mail archive and then ask more about it. I don't know anything about it yet so before I ask you something more about it I want to do a little homework myself. Thanks On Mon, May 16, 2011 at 5:31 PM, Marcus D. Leech <mle...@ripnet.com> wrote: > Let me give you the details this time. sorry for the confusion. > > USRP - The first version > Daughterboard - RFX2400 > > The signal source has the following settings. > 1. Sample Rate - 1Msps > 2. Waveform - Sine & Complex > 3. Frequency - 100kHz > 4. Amplitude - 10 > 5. Offset - 0 > > This source is connected to the USRP Sink directly. There is no other > block in between and not even a throttle. > > USRP sink settings: > 1. Interpolation - 128 > 2. Frequency - 2.5GHz > 3. Gain (dB) - 30 > 4. Side - A (Tx/Rx) The USRP is connected fine and works well with > benchmark_tx/rx tests. > > On the receiver side I use a GRC flowgraph with USRP sink and FFT block > only. > > USRP Sink: > 1. Decimation - 64 > 2. Frequency - 2.5GHz > 3. Gain (dB) - 10 > > FFT sink has proper settings too. > > I am not using any filters as I hope the SNR is high enough. > > Thanks > > On Mon, May 16, 2011 at 3:47 PM, Marcus D. Leech <mle...@ripnet.com>wrote: > >> On Mon, 2011-05-16 at 15:34 -0500, John Andrews wrote: >>> >>>> I am running it at 2.5GHz. >>>> >>> What magnitude are the samples you're feeding into the USRP sink? >>> >>> --n >>> >>> Also, by default the RFX2400 has a TX filter that's centered at >> 2.441GHz and about 85Mhz wide at the 3dB points. So, there'll be some >> attenuation >> at 2.5GHz, roughly 6-8dB or so. >> >> >> > It would be useful to see your .grc flow-graph files. Are you using UHD, > or "classic" (sorry if this has already been asked). > > I'll reiterate my earlier comments. The RFX2400, by default, has a > *hardware* SAW filter with a center frequency of 2.414GHz, and a nominal > bandwidth of 85MHz or so in the TX/RX path, so if you're running it at > 2.5GHz, you're somewhere on the skirts of the filter, which would lead > to attenuated output. This filter can be bypassed easily by carefully > cutting the traces going to FIL1, and populating C204 with a 30-100pF > SMD capacitor. > > > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > >
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