# Noisy APT images

**URL:** <https://www.ruby-forum.com/t/noisy-apt-images/239607>\
**Category:** GNU Radio\
**Created:** [March 6, 2014, 4:44pm UTC](https://www.ruby-forum.com/t/noisy-apt-images/239607 "2014-03-06T16:44:30Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [March 6, 2014, 4:44pm UTC](https://www.ruby-forum.com/t/noisy-apt-images/239607/1 "2014-03-06T16:44:30Z")

</div>

Hi,

I’m trying to receive APT images from NOAA with a QHA antenna and I  
received noisy images. I use a usrp source block, then a low pass filter  
with 50 kHz of cutoff and 20 kHz of transition width, then a WBFM  
receiver  
and a resampler connected to the audio sink. I think that I should  
change  
the parameters of the filter.

Regards,

Pablo.

---

<div class="post-metadata">

**Author:** ![pablo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ad7895/32.png) [@pablo](https://www.ruby-forum.com/u/pablo)\
**Post date:** [March 6, 2014, 6:22pm UTC](https://www.ruby-forum.com/t/noisy-apt-images/239607/2 "2014-03-06T18:22:19Z")

</div>

The WFM receive block includes deemphasis processing for improving the  
sound of broadcast FM reception. This is going to screw up your APT  
reception. You’ll be better off making your own WFM demod block – it’s  
just a quadrature demod followed by a low-pass filter.

–n

On Thu, Mar 6, 2014 at 7:42 AM, Pablo F. Alonso \<