For both manual and auto notch, the key seems to be to create two identical streams of signal data and apply different DSP to each. Stream 1 is totally focused on extracting accurate information about the interfering tones (frequency, amplitude, phase) regardless of any damage it may do to the audio signal. The damaged audio signal from Stream 1 is then thrown away. Instead, the tone information extracted from Stream 1 is applied very carefully to a 'clean copy' of the same data in Stream 2 to cancel the interference with minimal damage to the recovered audio.
73 from Ian GM3SEK >-----Original Message----- >From: Elecraft [mailto:[email protected]] On Behalf Of >Jim Brown >Sent: 01 August 2014 09:11 >To: [email protected] >Subject: Re: [Elecraft] [K3] Manual Notch Reconsidered > >I have no clue what the K3 does, but the slickest way to do this is to >first sense the frequency of the tone you want to notch, then create a >tone of the same frequency, shift its phase so that it is exactly 180 >degrees out of phase with the interfering tone, make it equal to the >interfering tone's amplitude, and add it to the signal. That will cancel >the tone with no other effect on the signal. That ain't easy, because it >must track the drift of both the TX and the RX and the varying strength >of the interfering signal, but with DSP, it IS possible. The beauty of >this technique is that it has NO effect on the desired signal -- it >simply cancels the interfering carrier. > >The alternative technique is to add a narrow band notch filter, which >MUST add phase shift that distorts the audio. The deeper the notch and >the narrower the filter, the greater the phase shift, and thus greater >distortion of the signal. > >These are fundamental concepts -- as my friends back home used to say, >"you cain't get no better" than this, :) and you must be very good >(and have the processor cycles available) to do it well. > >73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
