On Sat, 10 Dec 2005 20:51:01 -0500, Tom Rauch wrote:
>The noise
>is sampled, phase inverted, and combined with the noise from
>the main antenna at the same level as that noise. What you
>are really doing is setting the sensitivity of the sense
>antenna and main antenna to the same level at the distance
>and angle of the undesired signal, and inverting the noise
>exactly 180 degrees.
I agree with almost everything you are saying with respect to
cancellation of multiple sources and azimuth, except for one VERY
important thing. A noise canceller is SHIFTING the phase of the
noise sense antenna so that the resultant signal from the sense
antenna is 180 degrees out of phase from that same noise on the main
receiving antenna. That phase shift may be any number of degrees
from -infinity to +infinity (although -180 to +180 is enough). :)
The fact that it must be a phase SHIFT and not only a simple
polarity reversal is what makes the adjustment so tricky (and why it
must be re-balanced when the frequency changes very much).
This is a discussion we have had before, and as a practitioner in
both the audio and RF worlds, I am VERY bitchy about the difference
between polarity and phase. I know you design these things, and that
you do that very well, but the way we TALK about how they work is
very important to all of us understanding them. :)
Polarity is a two-valued function, and it is not related to
frequency or time. Phase has an infinite number of values, and it IS
a function of frequency and time. It is not possible to "invert the
phase."
73,
Jim K9YC
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|