The MFJ Noise canceler seems to work ok. As a quick band aid for the
contest.
I have an AN4 and have never been very impressed with it.
W0MU
On 1/22/2020 4:34 AM, Tim Shoppa wrote:
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
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