Rick, there are irregularities in my noise - and in the previous utility
line noises I've had at my QTH - that prevent any
predict-the-exact-time-of-the-noise-spike-in-advance algorithms.
Although my sample size is small the experts have told me that randomly
raucous 2-4 spikes every 120Hz I see is entirely typical of
lightning arrestor faults.
To show you the irregularities, here is the impulse envelope, recorded
during daylight on 1.8MHz with a 20kHz wide filter and AM demodulator.
Notice the overall 120Hz repetition, but inside that there is a
substructure where evidently several arcs occur in the lightning arrestor
each cycle and the exact number and timing of those vary from cycle to
cycle:
http://n3qe.org/n3qe-noise-structure.png
And here is a short audio wav so you can hear some of raucous noise
structure.
http://n3qe.org/SDRSharp_20200120_210017Z_18050000Hz_AF.wav
Tim N3QE
On Tue, Jan 21, 2020 at 11:50 PM Richard (Rick) Karlquist <
richard@karlquist.com> wrote:
> The Kalman filter still generates a blanking pulse like the conventional
> circuit. Feedback loops adjust the width and timing of the blanking
> pulse. "Amplitude" is not applicable. The frequency of the blanking
> pulse is supplied from the power line in the shack (EG 60 Hz). The
> feedback loops average over many pulses and therefore suppress QRM
> since it averages out in the long run.
>
> Again, this was all published many years ago.
>
> Rick N6RK
>
> On 1/21/2020 10:30 AM, Jim Brown wrote:
> > On 1/20/2020 2:28 PM, Richard (Rick) Karlquist wrote:
> >> In most cases, line noise is a repeating function with a frequency of
> >> 50 or 60 Hz. To make an effective noise blanker in a contest, you
> >> simply have to make a filter that only responds to harmonics of the
> >> line frequency and then generate the inverse function from a 50 or
> >> 60 Hz line clock.
> >
> > Unfortunately, that's too simple. For effective cancellation, that
> > inverse function must be precisely in phase (degrees, not polarity) and
> > equal in amplitude at each harmonic frequency.
> >
> > 73, Jim K9YC
> > _________________
> > Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
> >
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|
