On 08/26/2017 05:36 PM, Robert McGwier wrote: > At one time rational resampling meant that the interpolation and > decimation were each integers so the rate change is the ratio of two > integers and thus rational.
All integers are rational. But not all rationals are integers. 1,2,3, are integers and rational. The quotient of rationals is rational. Hence 1/2 = .5000000...... 1/3 = .3333333...... 2/3 = .6666666...... are all rational. > > If one or more of your inputs is fractional> I can input 1/2 in the rational resampler which satisfies the "rate change is the ratio of two integers and thus rational" - and the machine will reduce it to .5000000....... - which is also rational. > I believe you need the > arbitrary rate resampler. I've never used an arbitrary or fractional resampler. Maybe by an arbitrary resampler they mean it can used with either rational or irrational resampling ratios? And maybe a fractional resampler is to make a small adjustments to sampling rate - like on the order of a couple of percent? -- Cinaed > > Bob > > > On Aug 15, 2017 10:16 PM, "Cinaed Simson" <cinaed.sim...@gmail.com > <mailto:cinaed.sim...@gmail.com>> wrote: > > On 08/14/2017 07:14 AM, Jack White wrote: > > Hello, knowledgeable ones, > > > > I need to put together testbed satellite uplink using AX.25 > encoding and > > GMSK modulation. The flowgraph source is an Ettus USRP X310 with a > > WBX-120 daughterboard. > > > > The flowgraph is a modification of one used with a USRP B210. That > radio > > had handle different sample rates to the X310, so some level of > > resampling is required - in this case from the proposed 614.4ksps to > > 400ksps. > > > > I understand the premise of constructing the AX.25 packet, but I'm > > having real difficulty understand tagged streams and how the > tagging and > > the PDU format is affecting my transmission.> > > > > > > > > > > The disabled low-pass filter and the enabled and encircled rational > > resampler are my additions. The AX.25 line coding hierarchical > block is > > below. > > > > > > > > So, when I run the flowgraph and try to set a command from the > > groundstation, I get a huge load of buffer underrun errors in the GRC > > log: > > > > UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU > > > > UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU > > > > UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU > > > > UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU > > > > If I try sending the command again, I get a tP error, followed by more > > underruns. > > > > In my head, it looks like the USRP is expecting a combined sample of a > > certain length, but it doesn't get it. The buffer is more than half > > full. Then the next packet comes in, of the same length, and you > get one > > buffer filled with half of one packet and half of another. > > > > The USRP /is/ transmitting something, because I checked the > transmitting > > antenn400k/614.4a on a spectrum analyser. > > > > Can anyone help me understand the flowgraph, especially the tagged > > streams and PDU input, and get this working? > > > > Cheers, > > I don't really understand what you're doing but I have a couple of drive > by comments. > > The produce of 2 rationals is always rational - and the quotient of two > rationals is always rational. > > I would replace the 2 serial rational resamplers with one, namely, > > (8/1)*(400000/614400)=(8/1)*400/614.4) = 5.208333333333333/1 > > or > > 15.625/3 > > That is, interpolate by 15.625 decimate by 3. > > Since the sampling rate of the sink is 400000 Hz, then the sampling rate > coming out of the GFSK Mod needs to be 76800 Hz. > > And the baud rate out of the GFSK Mod would then be 76800 Hz/8 sps = > 9600. > > If reducing the 2 serial rational resamplers to one doesn't help, I > would poke the front side of GFSK Mod - add a throttle in front of the > GFSK and set it to 76800 Hz - see what happens- not recommend for > general use. > > And I would add a Message Debug to Tagged Stream Multiply Length Tag and > set the Length scalar to 1 - 512 times the packet_length seems high - > but then I don't know the packet_length either. > > -- CInaed > > > > > -- > > Jack White > > white.n.j...@googlemail.com <mailto:white.n.j...@googlemail.com> > <mailto:white.n.j...@googlemail.com > <mailto:white.n.j...@googlemail.com>> > > 07875 813 745 > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
