Hi Tom,
Thanks for your reply. It works.
I met another strange problem. When I use Wav file source --> audio sink,
I can hear the sound in the wav file clearly. However, when I want to hear
the file and transmit it using UHD sink at the same time, audio underrun
"aUaU" occur. The flow graph is like:
Wav file source --> Package Encoder --> GMSK Mod --> UHD sink.
--> Audio sink
Do you know what is the problem?
Jamie
On Fri, Apr 27, 2012 at 3:53 AM, Tom Rondeau <[email protected]> wrote:
> On Thu, Apr 26, 2012 at 12:08 AM, Jamie Wo <[email protected]>
> wrote:
> >
> >
> > On Thu, Apr 26, 2012 at 5:12 AM, wayne roberts <[email protected]>
> > wrote:
> >
> > Hi Wayne,
> >
> > Thanks for your reply. My responses are:
> >
> >
> >>
> >> I was messing with the same thing myself.
> >>
> >> First off, i'm not sure the packet decoder outputs in a real-time
> fashion
> >> to drive an audio sink. Try a scope sink to see how often the packet
> >> decoder output updates: is there a better way?
> >
> >
> >
> > I am not sure the real-time fashion to drive an audio sink either, but
> > there should be a way to support it, I guess. I ran the flow graph and
> saw
> > the update time interval from a scope sink is 3 - 5s . Is this too long?
> Do
> > you know what does this update time mean?
>
> Yes, these run in "real-time." If they didn't, you wouldn't be
> properly able to transmit or receive on an actual piece of hardware.
>
> >> On the GMSK demodulator side, I would think its best to observe the
> signal
> >> going into the demodulator, from uhd rx source. To see it in time
> domain,
> >> you can use Quadrature Demod -> throttle -> scope sink, making sure
> signal
> >> is centered at 0 and is reasonable distortion free. To be sure what its
> >> supposed to look like, you can put on the transmitter side Quadrature
> Demod
> >> -> throttle -> scope sink on the output of GMSK modulator.
> >>
> >> And of course you can put an FFT sink right on the UHD source to see it
> in
> >> frequency domain. On the transmitter side, to UHD sink, I have found
> the
> >> GMSK modulator outputs signal level near the maximum, meaning some
> transient
> >> peaks could cause clipping on USRP transmitter, so it might be prudent
> to
> >> put a multiply const (with 0.99 or so) just before going to UHD sink.
> >
> >
> > I used Quadrature Demod -> throttle -> scope sink on the receiver side to
> > see the signal going into the GSMK demod after uhd source. Also I
> > used Quadrature Demod -> throttle -> scope sink after the output of GMSK
> > mod. The time and frequency domain outputs are attached. Theoretically,
> > these two output should be similar or the same, However, they are quite
> > different after travelling over the air. Can you see any problems from
> the
> > figures?
>
> Don't use a throttle when you have a block that's already setting the
> rate of your flowgraph. The USRP receiver is controlling that. Having
> two rate-controllers in there is at best not needed and at worst
> actually screwing up your receiver.
>
> Tom
>
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