Notch Filter

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VK6XT's picture
Last seen: 9 hours 2 min ago
Joined: 2010/03/14 - 02:43
Notch Filter

Recently I was listening for the PS-46 Balloon, receiving wspr and jt9 simultaneously. There were some strong wspr signals in the passband, so I used my notch filter to remove 1400 to 1600 Hz whilst listening on 1800Hz. The general idea being to prevent the wspr sigs activating AGC in the receiver and reducing the overall gain. I noticed that some wspr sigs were still visible on the waterfall. What is really surprising to me is that one of the sigs appears to have improved from a -20 report to a -6dB report . This seems counter-intuitive....The notch filter actually improves S/N ratio ?? Wondering if anyone else has noted this ?