[TenTec] Noise Blanker Comparisons

[Ken Brown]

This is a HUGE subject. I expect that most of the comments will be 
subjective descriptions of how well a noise blanker worked for a 
particular person in a particular location, on various kinds of noise. 
It would be nice if we also had some details about the real workings of 
the noise blankers. For example, I can think of perhaps four ways to 
describe how each noise blanker works.

How is the blanking triggered? From a pulse detector in the IF of the 
same receiver the blanking is done in, or in a dedicated noise receiver? 
(In almost every amateur rig it will be the former, but this is not 
necessarily the best way to do it)

Is the triggering threshold adjustable? Or can it be changed a bit using 
selected resistor values?

Is the delay from the trigger to the blanking fixed, and what is the 
delay? Or is it adjustable.

Is the duration of the blanking fixed, and what is it? Or is it adjustable?

Where is the blanking done, and how much is the signal attenuated during 
the blanking? If the blanking occurs after many gain stages and filters, 
the noise can get spread out in time and require a longer duration 
blanking than if the blanking was done at at earlier stage in the signal 
chain. In most every amateur transceiver the noise blanker will be in 
the IF system long after a strong noise pulse can distorted and spread 
out. It would be better to have the blanker right at the antenna input, 
but then of course the triggering would have to be done with a dedicated 
noise receiver. What sort of envelope shape does the blanking have as it 
turns on and off.

And here is another that just occurred to me: Does some characteristic 
of the triggering, such as the noise pulse amplitude, dynamically change 
the delay or duration of the blanking?

Just some things to ponder. Much of what I have mentioned is not 
applicable to amateur equipment, but we can dream. The questions of 
delay and duration of the blanking are relevant and can be determined 
with the right instrumentation.

DE N6KB