Matt, I was trying to explain that using 8 as a decimation rate would complicate my rational resampler coefficients, not that it would give me less band. Anyway resampling seems too heavy for my processor and I decided to use filtering as you suggested. The problem is that I don't understand what is the difference between using an 8, 10 or 12 rate decimation (aside from the obvious band size difference), if and how they affect the measured power values. I used decimation 8 and the appropriate 8 MHz filter and measured a signal power of -44.42 dBm. I used decimation 10 and the appropriate 8 MHz filter and measured a signal power of -42.1 dBm. I used decimation 12 (which gives me a 8.333 MHz band) and the appropriate 8 MHz filter and measured a signal power of -47.07 dBm. As you can see there is a great difference between the 3 results, considering they are measuring the same band. I've read that using even decimation values that are not multiples of 4 result in an output of only one halfband (the low rate one), but I don't know how to interpret this information nor if it's even relevant to my case. What are your thoughts on this? Thanks.
Vlad. P.S.: I don't think my power measuring method is the problem: I unbuffer the filter's output, input it in a magnitude FFT block (fft squared) after which I buffer the resulting coefficients, sum them, divide the result by the buffer size and the sample time and transform the output value to dBm. --- On Tue, 11/16/10, Matt Ettus <[email protected]> wrote: From: Matt Ettus <[email protected]> Subject: Re: [Discuss-gnuradio] USRP2+WBX - How to use precisely an 8 MHz band? To: "Vladutzzz" <[email protected]> Date: Tuesday, November 16, 2010, 8:09 PM On 11/16/2010 09:36 AM, Vladutzzz wrote: > > Thank you all, for your replies! > I am a bit confused about the 10 rate decimation, which just gets one > halfband (the low rate one) - as explained in USRP2 FAQ. Does this affect > the power level that I will later measure? > I thought about using 8 which is also a multiple of 4, but it is a very > unfortunate fraction and I would like to keep as much as possible from the > original band, I don't understand this. Decimation of 8 will give you more bandwidth, not less. > plus the 10 rate will also decrease the load on my processor. > So, is the 10 rate decimation in fact a good candidate for what I'm trying > to do or I'm better of using 8 with a 1.5625 rational resampler? Why do you need to resample? Just use a filter of 8 MHz bandwidth. Matt -- View this message in context: http://old.nabble.com/USRP2%2BWBX---How-to-use-precisely-an-8-MHz-band--tp30191243p30238749.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
