-----Original Message----- Would this type of noise canceler not work on "white" noise also ? _______________________________
The simplest answer is no. White noise typically arrives from random directions, with random phases, random polarizations, etc. etc. etc. and are usually from thermal and uncorrelated sources. The principle of operation of these phasing units IS THAT THEY CAN BE PHASED to eliminate unwanted signals since they are from a sufficiently point like source that a null can be tuned on top of them. How is this done? You can arrange to add an interfering signal 180 degrees out of phase with one from the intended antenna while not killing the signal of interest to the point it is not heard. In other words, you increase the signal to (signal+interference) ratio. To the extent that this is automated, it is a "smart antenna". The importance of them having equal responses to the interferer so that simple phasing works is a tricky business. If amplification is required to do this, then you have the myriad problems (IP3, IMD, DR, MDS, etc) to deal with in this new system. Since we are not asking for a perfect null, but some serious suppression, these conditions can be relaxed. If the noise source is localized or coming from a direction that is not nearly collinear (within the 3dB beamwidth of say a directive antenna) with the signal of interest, it can be nulled with these phasing methods irrespective of its power spectral distribution, white, poisson, tone, etc. This is all reasonably complicated as you can see. Bob N4HY _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
