I have never found a noise blanker to be of particular value, if any at
all, on general power line hash [the "grass" along the baseline of a
panadapter. At our prior home in Auburn CA, I had a 3-phase ~70 KV
transmission line on running across the lower end of the property that
connected a series of hydroelectric plants above and below us, and two
3-phase 112 KV transmission lines on towers about 1/4 mile away. The 70
KV line was essentially quiet. The 112 KV lines was perhaps S3-4 on 80
and had a fairly high frequency sound ... I guess from the 3-separate
phases with peaks occuring at 360 Hz. The K3 NB was ineffective against
it. With the level set high enough to affect the noise level in the
headphones, SSB was highly distorted and CW was chopped up.
Here in NV, we are about 1/2 mile from a 500 KV 3-phase transmission
line connecting a power plant in Patrick NV to someplace up in OR,
probably along the Columbia. It is fairly quiet, S2-3 on 80, and again
seems to be high frequency enough that the K3 NB is ineffective. I've
concluded that, while technically it all is impulsive [arcs on voltage
peaks], the peaks must overlap enough and/or are of a high enough
frequency that the NB either can't find them or punches too many too big
holes in the signal. It might be more effective on noise from a single
phase line, don't know.
I rarely hear ignition noise from spark plugs anymore, however the
landscape maintenance crew showed up earlier this spring to aerate and
de-thatch the grass. Their aerator gizmo had an old 7 HP engine with
strong ignition noise. The NB took all of it out just fine at very low
settings.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
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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