Using your perfect samples (the ones you get with decim=8), can you
try low pass filtering them (without decimating) to the equivalent
width that you'd get with the decim=256 setting, and then plotting
them?
Maybe it's not perfectly round because with the narrower filter, we're
losing more of th
On 3/17/07, Eric Blossom <[EMAIL PROTECTED]> wrote:
I'm waiting on hearing the results of low pass filtering the "perfect
samples" without decimation, and seeing if the problem still exists.
I was driving home from work and was remembering that GMSK has a good
amount of ISI built in. When look
On Sat, Mar 17, 2007 at 08:00:59AM -0700, Mike Garcia wrote:
>
> Thanks Eric. That makes sense. I'm still learning about gnuradio so excuse
> my naivete. Could the distortion be cause by the CIC filters? I understand a
> CIC filter needs some amount of bit growth. If the LSBs are truncated
> inste
ay be
unavoidable but might explain the distortion you're seeing.
Mike
-Original Message-
From: Eric Blossom [mailto:[EMAIL PROTECTED]
Sent: Friday, March 16, 2007 10:41 PM
To: Mike Garcia
Cc: discuss-gnuradio@gnu.org
Subject: Re: [Discuss-gnuradio] A medley of questions
On Fri, Mar 16,
On Fri, Mar 16, 2007 at 08:07:33PM -0700, Mike Garcia wrote:
> Hi Eric,
>
> I just joined the gnuradio discussion but I found your question about the
> GMSK amplitude distortion interesting. My guess is that it's aliasing. GMSK
> has good spectral efficiency but it still has spectral sidelobes tha
Hi Eric,
I just joined the gnuradio discussion but I found your question about the
GMSK amplitude distortion interesting. My guess is that it's aliasing. GMSK
has good spectral efficiency but it still has spectral sidelobes that get
folding into your desired passband when you decimate. I would sug
On Wed, Mar 14, 2007 at 10:24:10PM -0400, Steven Clark wrote:
> You're right, I was normalizing for the purposes of plotting. Here's what
> the raw complex samples look like:
> http://img490.imageshack.us/img490/3225/rawbasebandvv9.jpg
> +/- 2400 or so.
> and here's that other plot regenerated:
> h
You're right, I was normalizing for the purposes of plotting. Here's what
the raw complex samples look like:
http://img490.imageshack.us/img490/3225/rawbasebandvv9.jpg
+/- 2400 or so.
and here's that other plot regenerated:
http://img249.imageshack.us/img249/9520/d256unnormalizedkd4.jpg
signal is
On Wed, Mar 14, 2007 at 09:47:20PM -0400, Steven Clark wrote:
> Plots of USRP decimation woes:
> input is GMSK waveform @ ~30ksym/sec, BT = 0.35, no noise added
> using decimation rate of 16:
> http://img339.imageshack.us/img339/4467/d16cz9.jpg
> top plot is complex baseband, bottom plot is amplitu
Plots of USRP decimation woes:
input is GMSK waveform @ ~30ksym/sec, BT = 0.35, no noise added
using decimation rate of 16:
http://img339.imageshack.us/img339/4467/d16cz9.jpg
top plot is complex baseband, bottom plot is amplitude of top plot
some amplitude variations noticeable, but fairly minor.
On 3/14/07, Steven Clark <[EMAIL PROTECTED]> wrote:
GMSK is a constant amplitude modulation. So unless I am misunderstanding
something (which is entirely possible), if you plot the complex baseband
signal with real for X and imag for Y, the result should be a
constant-amplitude circle regardless
There is always an unknown phase between the transmitter and receiver.
In addition, the clocks between the transmitter and receiver are never
running at exactly the same frequency. FWIW, the oscillator on the
USRP is spec'd to 50ppm.
Eric
GMSK is a constant amplitude modulation. So unless I
On Wed, Mar 14, 2007 at 05:54:03PM -0400, Steven Clark wrote:
> >> I'm using usrp_rx_cfile.py. So hopefully I'm just looking at the raw
> >complex
> >> baseband coming across USB.
> >
> >No surprise, you're not sampling at the center of the symbols.
> >
>
>
> Eh? I'm using the -f command line arg
On Wed, Mar 14, 2007 at 04:53:58PM -0400, Steven Clark wrote:
> Eric: many thanks for your responses. My responses below:
>
> On 3/14/07, Eric Blossom <[EMAIL PROTECTED]> wrote:
> >
> >On Wed, Mar 14, 2007 at 03:45:32PM -0400, Steven Clark wrote:
> >> Hi all-
> >> Two very different questions for
Eric: many thanks for your responses. My responses below:
On 3/14/07, Eric Blossom <[EMAIL PROTECTED]> wrote:
On Wed, Mar 14, 2007 at 03:45:32PM -0400, Steven Clark wrote:
> Hi all-
> Two very different questions for you:
>
> 1) As a test, I am sending a GMSK signal (created by a signal generat
On Wed, Mar 14, 2007 at 03:45:32PM -0400, Steven Clark wrote:
> Hi all-
> Two very different questions for you:
>
> 1) As a test, I am sending a GMSK signal (created by a signal generator,
> very low noise) at low symbol rates into the USRP and plotting the complex
> baseband that reaches the PC.
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