# Strange Response of a fir1 Filter in Matlab

i have been tinkering with some fir filters to bandpass-filter a signal. Even though the filter looks pretty descent in frequency domain, i receive a quite strange "filtered" signal in time-domain. I think, i'm oversseing something simple... Maybe one of you knows what i am doing wrong.

First of all, here's the code:

Fs          = 200; % hz
nyquistFreq = Fs/2;
frange      = [45 55];
order       = round( 30*Fs/frange(1) );
filtKern    = fir1(order,frange/nyquistFreq);
filtSignal  = filter(filtKern,1,signal);


I plotted the data stored in signal and filtSignal into one plot and the filter-shape is received at the beginning of the filtered signal:

Here's a picture of the filter in time-domain, in frequency-domain and in frequncy-domain with logarithmic scale. According to the plot in frequency domain, the cut-off frequencies fit pretty much what i requested...

Thank you so much, i appreciate every input!

• Are you providing all the code used? It is not clear how the filtSignal gains so much energy. It also will help if you can describe your signal and what you expect as an output – Engineer Dec 28 '19 at 13:37