Hi A few years ago I had an idea for a filter that would remove the back ground noise on HF. I was wondering if a digital signal processor does this or if some one had made a commercial filter to do this. It would be a help to catch those stations that fall below the noise level! God bless, Mark WZ0K God loves you! My personal prayer book. Add your prayer or pray for others at the following link. http://prayerbook.homewithgod.com/cgi-bin/prayerbook/multi.pl?131961113534708:24:0 http://lists.topica.com/lists/funhamradio. http://funhamradio.bloki.com