[Discuss-gnuradio] Issue with MMSE interp. filter (broken?)

[Colby Boyer]

Hi All,

Recently I've been using the MMSE interp filter. I found that when I shift a signal by a fractional amount of 0 (or anything really), the signal goes way off! I would expect SOME difference, but not this much...

Some example output.

Mu:0 In:(-1.67869,0.480381) Out:(0.0418351,-0.16734)

Mu:0 In:(-1.23772,-0.104519) Out:(0.16003,-0.115883)

Mu:0 In:(-1.7598,-0.0618457) Out:(0.0986395,-0.33428)

On the imgur links are two Re-Im scatter plots of a bpsk signal, one with the fractional shift of 0 and the other with a fractional shift of 0.1 The points with 'x' are the resampled points and points with 'o' is the original signal. As you can see, the mmse fractional interp more or less destroys the signal! Unless I'm using it wrong!?

Any comments?

imgur: http://imgur.com/a/w98SX top picture is 0 delay, bottom is 0.1 delay.

Thanks!
Colby