On Mon, Jan 28, 2008 at 02:42:33PM -0600, Richard Jaeger wrote: > On Jan 28, 2008, at 1:32 PM, Eric Blossom wrote: > >> On Mon, Jan 28, 2008 at 09:43:13AM -0600, Richard Jaeger wrote: >>> I have been playing with a number of the examples - FM NB and WB >>> receivers, >>> AM receiver, etc. >>> The sample rate appears to default to 64 MSPS, but I have been unable to >>> find where that default rate is set. >>> Where is it defined? Can it be changed from the examples themselves? >>> >>> For example, 64MPS is not a proper subsample rate for the FM broadcast >>> band. >>> It results in aliasing and should be reduced. >>> >>> Dick... >> >> It's not settable, but is determined by the master oscillator on the >> USRP. If you're using the Basic Rx or LF Rx daughterboards, yes you >> will need some kind of preselector. If you're using one of the RFX or >> TVRX boards, the 64MS/s sample rate won't be a problem. >> >> Eric > > > Eric, > > Thanks for the quick reply.
No problem. Be sure to use the "Reply-to-all" command in your mailer to ensure that both the sender and the list get a copy. > So, then I guess the ADCs run at the maximum sample rate all the time. > I thought I saw some other Python examples that set the sample rate to > 20MSPS. I may have misinterpreted what I was reading. I'm new to Python. There is some very old code kicking around that we used with the Measurement Computing PCI-DAS 4020/12. It was a 20 MS/s device. > Once you've sampled the FM band at 64MSPS, I think it's too late to do > anything to solve the aliasing problem. > The spectrum has already been folded. One would need to use some form of > down conversion before the ADC's. Yes, that's why I mentioned the TVRX and RFX-* daughterboards. The Basic Rx and LF Rx are really designed to be used with external converters, filters, etc. > Is the oscillator running at 64 MHz, or is it divided down from a higher > frequency? I guess can inject an external oscillator if needed. It's running at 64 MHz. > My primary application is going to be low frequency phased antenna > arrays (Ham radio - 160M), so the high sample rate is ok (but not > really needed.) I can just decimate right away. Good. I recommend that you take a look at gnuradio-examples/python/multi-antenna/*.py. They use two Basic Rx daughterboards and 4 DDCs to generate 4 streams of coherent samples -- perfect for beam forming, etc. Eric _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
