Thanks for the mention of the Collins document. I had not seen it and after a
search and finding it, I was amazed at how much of it was similar to what I
established independently.
If you happen to look at the bottom of my QRZ bio you can see the mobile rig
belonging to a boyhood neighbor. He gave me my first exams, but I wouldn't call
him an Elmer in the mentoring sense. He built the mobile because a powerline
running through his property prevented him from hearing anything. That was
until Collins came out with their noise blanker for his 75A-4. (I never
understood why he didn't just move but I think his trust fund income came after
he moved there.)
Wes N7WS
On 6/14/2019 11:33 AM, Bob McGraw K4TAX wrote:
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
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