David et al;
My statement is almost word for word from the Elecraft K3 manual. And
some from work done by Art Collins and company at Collins Radio. They
prescribed the function of a Noise Blanker as follows:
"The following operational requirements were kept in mind:
1. Reduction of ignition noise from vehicles.
2. Reduction of power line corona noise occurring at 120 CPS repetition
rates.
3. Reduction of local thunderstorm disturbances.
4. And, in general, reduction of any man-made noise which is impulsive
in nature.
Basically, all the above forms of noise interference are impulsive
functions with repetition rates than can extend up to 100 KC in the case
of the strokes in a thunderstorm."
Those are my sources.
Again both descriptions use repetitive pulse rates which are impulsive
in nature. In order for a NB to function efficiently it is best
suited in a wide band signal path that is not restricted by filters.
Hence a wide IF stage of the receiver before any filtering.
As to thunderstorms, since lightning contains many pulses in a single
stroke, the NB is suited to minimize those pulses while at the same
time, the bulk of the strike energy is affecting the receiver in other
means. Namely AGC. Many receivers suffer grossly from this phenomenon.
Fortunately Elecraft and Tentec took actions with their designs to
minimize this phenomenon based on the work of Rob Sherwood. And
regarding thunderstorms, there is a clear difference in the stroke and
content of such for a "local thunderstorm" as compared to the noise
from distant thunderstorms several hundred miles away. The distant
thunderstorm is affected by propagation and may have several wave fronts
with different arrival times where as a local thunderstorm only has a
single wave front. Hence the waveform is quite different and the means
to suppress such will be different.
73
Bob, K4TAX
On 6/14/2019 12:24 PM, David Woolley wrote:
The below statement surprised me. That is not how noise blanking
normally works; normally it will suppress any wide band pulse. The
typical arrangement uses a high bandwidth, low delay, path, to detect
the pulse. It can then mute the signal path by the time the pulse
gets through the narrower filters on the main path. That will happen
with single, or randomly spaced spikes.
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