K3 Noise Blanker
From Zerobeat
The K3 Noise Blanker is a hardware device that is included with the base K3 at no extra charge. This blanker was designed at considerable effort starting with the best known designs available as models. This includes but was not limited to the 4-NB noise blanker from the Drake 4C series of the 1970's, which is one of the most regarded hardware noise reduction units ever designed for amateur radio equipment.
From the K3 user manual:
There are two noise blanker subsystems in the K3: the KNB3 module, and a DSP-based blanker The KNB3 is a narrow I.F. pulse blanker that plugs into the RF board. Its broad input bandwidth ensures minimum stretching of fast noise pulses, so it’s ideal for suppressing noise from power lines, thunderstorms, and auto ignitions. The DSP blanker can be used on many other types of noise, including radar and other noise with complex waveforms that might cause heavy intermodulation if an I.F. blanker were engaged. Using the two blankers in combination is often extremely effective. The KNB3 includes a triple-tuned and pass/time-delay filter, wide-range AGC, and a noise gate. You can think of the noise gate as a switch that is normally closed, allowing received signals to pass unimpeded. When a noise pulse appears, it is amplified to a high level and used to trigger a one-shot circuit. This opens the noise gate very briefly (from 5 to about 100 microseconds) to blank the noise pulse. Both the threshold at which blanking action occurs and the length of time the gate is opened are under control of the operator.
Noise Reduction parameters Lyle Johnson kk7p at wavecable.com Sat Dec 22 10:31:48 EST 2007
Can someone enlighten me about setting up the NR parameters....hope I can explain myself ok!
The NR has changed with time and may continue to do so. As a result, the manual is general in its treatment. The overall rule is "more is more."
NR is more properly Signal Enhancement rather than Noise Reduction. The distinction is subtle but important if you wish to understand how it works and how to best apply it. If ti were noise reduction, the implication is that it passes everything until it figures out what is more likely to be noise, which it then attempts to suppress. Since it is signal enhancement, it tends to pass nothing until it figures out that which is more likely signal, which it then attempts to pass.
With this understanding there is one more concept I must explain: correlation. This is the degree to which a signal is similar to itself; conversely, it can be used to figure out how noise is dis-similar to itself (more random). This is the basis on which NR works.
In the current implementation of the K3, we have four (4) basic NR filters. These are displayed as F1..F4. F1 is the gentlest, F4 the most aggressive. Recalling that the filters tend to suppress everything until they can sort out what is probably a signal, there is some time delay involved in their application. Further, especially with voice signals, some components of the signal may not be recognized as well as others. THis gives rise to distortion.
So, we added a second field to the NR. This is the -1..-4 which specifies a certain amount of "bleed through" of the original signal. This reduces the apparent distortion and delay, but limits the ultimate S/N improvement. -1 provides the least distortion but limits the S/N improvement on weak to moderate signals to about 6 dB. -4 provides no "mixing" whatsoever and can result in dramatic S/N improvements, but at a cost of slight time delays and increased distortion.
NR is not appropriate for very weak signals, so a -1 or -2 is best if you wish to hear them.
Having saids al this, the correct way to use the NR is to listen and adjust it for the best compromise between noise reduction and distortion. Everyone is different in this regard. Some tolerate noise better than others, while some don't tolerate distortion very well at all.
I live in a quiet location, and use NR1-2 as my most common setting. This is low in distortion, allows me to hear weak signals, and shows no apparent delay as I tune through the bands. On the rare occasions when things get noisy here, I crank it to higher values.
Lyle KK7P
