[Elecraft] K3 and W2IHY EQ Plus!

[Lyle Johnson]

>> My primary goal was to eliminate the high level of background 
>> noise from my VHF amplifiers when I operate SSB mode.
>>     

There are two main approaches to helping mitigate shack noise from Tx 
audio: Noise Gate and Downward Expansion.

A Noise Gate, such as is used in the K3, acts much like an FM squelch 
does on receive.  It looks at Tx audio amplitude and if a signal exceeds 
that amplitude, it opens the audio path for a certain period of time.  
Whenever an audio peak exceeds the threshold, the timer is 
re-triggered.  Thus, continuous speech will keep the gate open.  The 
timer is necessary to allow softer parts of speech to pass without 
distortion.

Thus, the Noise Gate is not a clipper or "waveform modifier" and 
introduces no crossover or other distortion when it is activated.  In 
this case, the speech overrides the noise source during speech, and the 
timer silences the audio path when there is no speech.  However, if the 
threshold is too high, then "leading edge" distortion may result.

A Downward Expander changes the gain (slope, or transfer function) of 
the input amplifier for signals below the threshold.  This can result in 
crossover and other distortion for the low-level components of speech.  
On the other hand, it may also result in reduced amplitude of the noise 
source itself even when speech is present due to the slope of the 
downward expansion.  Gating in the form of clipping occurs when the 
downward expansion slope results in zero gain.

The most common misadjustment of the Noise Gate is to set the threshold 
too close to the noise source's level. This can result in the noise 
source triggering the audio, resulting in a scratchy or staccato 
effect.  In most cases, *increasing* the threshold beyond that point 
will result in the desired "squelching" of the noise source, while still 
allowing speech to pass.

73,

Lyle KK7P