I have an old Ten-Tec Paragon here, Bill. The noise blanking is done in the
first IF ahead
of all the narrow second IF filters and is extremely effective on impulse
noise provided that
the band is not full of strong signals (this is oftentimes the case on 160
meters in the wee
hours before sunrise). This compares to the blankers on most of the JA rigs
I've used
(even the $4K FT-1000D) , which for the most part appear to be useless.
73 de Mike, W4EF...............................
>
> The noise blanker comment above is related to what is referred to as
ringing and Heisenberg's Uncertainty Principal. This is a mathematical fact.
Unlike theories and laws this is an undisputable fact.
>
> The product of bandwidth and pulse width can't be less than 1. In this
case frequency is in Hertz or cycles per second.
> In quantum mechanics these are expressed as (energy, time) or
> (momentum, position) and and Planks Constant instead of the constant of 1.
> Sometimes other factors appear depending on the space used. Physicist like
using K-space at times or frequency in radians per second which throws in a
factor of 2*PI as well. But all these expressions go back to the
relationship of bandwidth and pulse width.
> That is to say if you have a filter passing a tone burst ( a dit) that is
0.1 second long then the filter will have to have at least 10 Hz band width
to pass it. If you have a shorter burst than 0.1 seconds long then the
filter will stretch it to 1 second (ringing).
> For the same reason a noise blanker needs to be preceded with a wide
bandpass filter so that the short burst may be detected and eliminated
(blanked) in such a way that very tiny bit of time where the signal is not
passed is not detectable after narrower filtering and detection.
>
> Take a look at this web page:
> http://www.mathpages.com/home/kmath488/kmath488.htm and note equation 2.
>
> The method of filtering does not matter. It is the bandwidth.
>
> merry Christmas and
> 73
> Bill wa4lav
>
>
>
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