Re: [Discuss-gnuradio] GMSK receiver question, USRP tuning?

[Dan Halperin]

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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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