The effect we observe doesn't seem to be a non linear effect due to high signal amplitude. Lowering the amplitude doesn't solve the problem. For example, when we transmit a 1 MHz tone we can see that a spurious tone appears at -3 MHz (referred to the carrier frequency) when using an interpolation rate of 16 (4x at the AD9862 and 4x at the FPGA). So, that spurious seems to be aliasing. Can you corroborate this?
Óscar El 19 de enero de 2010 03:00, Eric Blossom <e...@comsec.com> escribió: > On Mon, Jan 18, 2010 at 11:46:53PM +0100, Óscar González Fernández wrote: > > Dear all. > > > > We are trying to setup a MIMO node using a USRP motherboard and two > > xcvr2450. Theoretically the maximum allowable transmission bandwidth when > > using two antennas simultaneously is 4 MHz or 8 MHz if using a single > > antenna (limited by the bandwidth of the USB port). However, we have seen > > that the maximum affordable aliasing free bandwidth is approximately 2 > MHz > > due to the poor antialiasing performance of these filters. As we need > more > > bandwidth, the question is: Do you think it could be possible to put a > > better interpolation filter that fits into the FPGA while mantaining two > > transmission and reception chains? > > What is the amplitude of the signals you're sending? > If you need more linearity, try sending smaller signals. > > Eric > >
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