# Confusion, help please **URL:** \ **Category:** GNU Radio\ **Created:** [March 3, 2015, 12:30am UTC](https://www.ruby-forum.com/t/confusion-help-please/234410 "2015-03-03T00:30:37Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [March 3, 2015, 12:30am UTC](https://www.ruby-forum.com/t/confusion-help-please/234410/1 "2015-03-03T00:30:37Z")
Hello all, I just had a quick question regarding the polyphase channelizer. As a start, I’m trying to divide an input spectrum into 6 channels of equal width. My sample rate for now is 5 MHz and the way I’m calculating the taps as follows: firdes.low\_pass2(1.0, samp\_rate, samp\_rate/(nchan_2.15), samp\_rate/(nchan_13.8),attenuation\_dB = 10, window = firdes.WIN\_HAMMING) The channels are being divided equally now, but the first channel behaves very different from the rest, it becomes super wide for a moment, and then shrinks back to normal just like the rest of the channels and this happens repeatedly. I’m honestly stumped as to what the reason could be, so would really appreciate if anybody can point me in the right direction or at least clarify why this is happening. You can find the images here: [http://tinypic.com/a/3e8so/4](http://tinypic.com/a/3e8so/4) Thank you, Best, Ali ---
**Author:** ![alirose](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bc79bd/32.png) [@alirose](https://www.ruby-forum.com/u/alirose)\ **Post date:** [March 3, 2015, 9:43am UTC](https://www.ruby-forum.com/t/confusion-help-please/234410/2 "2015-03-03T09:43:57Z")
Hi Ali, that’s interesting. Would you mind sharing the flow graph that you use? Greetings, Marcus PS: Although using adblock plus, before I see every other picture on tinypic, I get stuff like casino advertisment, and similar. Could you use any image hoster that doesn’t block view on the pictures with advertisement? I found [imgur.com](http://imgur.com) to work fairly well. ---
**Author:** ![alirose](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bc79bd/32.png) [@alirose](https://www.ruby-forum.com/u/alirose)\ **Post date:** [March 4, 2015, 8:19pm UTC](https://www.ruby-forum.com/t/confusion-help-please/234410/3 "2015-03-04T20:19:56Z")
Hey Marcus, Thank you for replying back! Absolutely, I’ve posted my flowgraphs on [imgur.com](http://imgur.com) now. Here’s the link: [http://imgur.com/a/a0KCX](http://imgur.com/a/a0KCX) Also, for some reason, I think it could be because I’m using the Spectrum analyzer’s tracking generator? P.S I’ve done a couple of changes since my last email: 1. My sample rate is now 10M 2. My filter taps for the channelizer are being calculated as you told me earlier: firdes.low\_pass(1.0, samp\_rate, samp\_rate/(nchan_2.15), samp\_rate/(nchan_4.5)) 3. Assuming that the tracking generator is at fault, and everything else in the design is good, it works perfectly fine for a 2M sample rate, but when I try using a higher sampling rate say 10MHz, I get strange results which leads me to believe that there’s something wrong in my design, though I just can’t put my finger on it. One of the pictures is when I’m asking the channelizer to make a total of 8 channels, and the other one is where I’m asking the channelizer to create 20 channels. (Only 6 of which are being plotted in both cases). Is the way I’m calculating my filter taps at fault here or is it perhaps something else? Best, Ali Date: Tue, 03 Mar 2015 09:42:19 +0100 From: Marcus M?ller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Subject: Re: [Discuss-gnuradio] Confusion, help please Message-ID: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Content-Type: text/plain; charset=“windows-1252” Hi Ali, that’s interesting. Would you mind sharing the flow graph that you use? Greetings, Marcus PS: Although using adblock plus, before I see every other picture on tinypic, I get stuff like casino advertisment, and similar. Could you use any image hoster that doesn’t block view on the pictures with advertisement? I found [imgur.com](http://imgur.com) to work fairly well. On 03/03/2015 12:27 AM, Ali R. wrote: > Hello all, > > I just had a quick question regarding the polyphase channelizer. As a > start, I’m trying to divide an input spectrum into 6 channels of equal > width. My sample rate for now is 5 MHz and the way I’m calculating the > taps as follows: > > firdes.low\_pass2(1.0, samp\_rate, samp\_rate/(nchan_2.15), > samp\_rate/(nchan_13.8), > attenuation\_dB = 10, window = firdes.WIN\_HAMMING)