[Elecraft] [k3] NB & Chirp [+ general discussion of DSP vs. IF noise blanking]

[Wayne Burdick]

Wes,

The DSP NB causes some artifacts at its higher settings. This is an  
unavoidable side effect of signal processing.

The DSP NB is applied after the crystal filter, so the bandwidth is  
already constrained, removing some of the inherent characteristics of  
noise pulses, including their rise/fall time and shape. Thus it is  
harder for the DSP to distinguish between signal and noise. On the  
other hand, this is the only way to remove narrow-band noise (e.g.,  
noise that appears every 10-15 kHz on a particular band, rather than  
blanketing the entire band). The DSP NB also has the advantage of not  
being "pumped" by distant signals outside the crystal filter.

The IF NB has the opposite situation to contend with. Noise pulse  
shape and rise/fall time are preserved, so they can be effectively  
gated. But if you set the threshold too low, the IF NB's noise gate  
can be modulated by very strong adjacent signals.

By including both, we give the operator the ability to optimize the  
ratio between IF and DSP blanking, which can be extremely effected as  
attested to by many customers.

73,
Wayne
N6KR

Wes Stewart wrote:

> Thanks Merv,
>
> So it isn't my imagination as some have inferred.