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Re: [Discuss-gnuradio] GMSK receiver question, USRP tuning?
From: |
Dan Halperin |
Subject: |
Re: [Discuss-gnuradio] GMSK receiver question, USRP tuning? |
Date: |
Tue, 18 Dec 2007 13:03:36 -0800 |
User-agent: |
Thunderbird 2.0.0.6 (X11/20071022) |
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George Nychis wrote:
> The decimation should not affect the amplitude of the waves, right?
> Which if you look at the graph, the GMSK receiver has ~4x the amplitude.
Actually, it may. Imagine you decimate by a factor of 4, that's sort of
like adding every 4 samples together -- amplitude grows by 4.
Now, I think there is (or there ought to be) some code that, at lower
decimation levels, shifts which bits of the register it outputs
(presumably, takes 2 more significant bits) to keep the amplitude
constant, but that code may not be there in your new version, or the
FPGA might do it differently that I imagine.
> I agree that the decimation has affected what looks like the frequency,
> but otherwise it should look the same and not affect my ability to
> decode it. Something else seems different between test_usrp_standard_rx
> and the GMSK receiver.
If the decimation factor is not correct there's no way it's going to work.
- -Dan
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