By: Bob Wolbert, K6XX 

July, 2026

Elecraft introduced “SSNR”, (Spectral Subtraction Noise Reduction) via software update
during April. This marks a huge step forward in the evolution of calculation-based noise
elimination algorithms for HF radios. Unlike previous systems that offered limited results
targeting ragchewers, generally only producing more pleasant copy from moderate- or strong-signals, the new SSNR actually pulls usable signals out of overwhelming noise (up to a point, of course).

My requirements as a contester/DXer are different than ragchewing. I must pull weak,
uncopyable signals up to the point where callsigns are decipherable. This is while 
wearing headphones and concentrating strictly on simple exchanges. Toward this goal, I’ve
evaluated noise reduction (NR) processing since “deep in the last century”, when Icom
introduced its first NR hardware. I spent hours adjusting the NR on FT1000MPs of all flavors, then repeated these efforts with the K3 & K3S. Universally, my favorite NR setting has been “OFF”—NR did not accomplish my goal. The situation changed with K4’s SSNR: signals now jump out of the noise, from “is something there?” to “got it!”.

Operation

Getting SSNR running in [on?] your K4 is simple. Load the latest radio software (version 38 or newer) in the normal fashion. Tune in a signal, preferably weak and buried in noise. Tap the “NR” button. Listen… Long-hold the “NR” button on the front panel. Twist VFO A and adjust the aggressiveness of the NR routine for best results. That’s it. Different bands at different times with different antennas and different signal/noise ratios have different optimum aggressiveness levels. This level is subjective—go too far and the DSP artifacts become annoying—but I’ve found that the more time spent using NR, the more aggressiveness my ears allow. The improvement has seemingly increased over time.  

Optimum fidelity is not necessarily the same as best copyability. When signals are strong, you may determine that the older NR system (LMS; Least-Mean Squared) works better (or revert to OFF!). Toggle between SSNR and LMS by long holding the “SSNR” soft button on the K4NR screen, accessed when the NR physical button is long-pressed. 

SSNR in Action: SSB

Single sideband offers the most dramatic results. Weak signals, fading away completely into the noise, often become solid when SSNR is engaged. At the best-copy setting, there generally are noticeable DSP artifacts, which usually disappear on signals with better signal/noise ratios. This means that NR may be left active most of the time.

SSNR in CW

Morse also benefits. In my experience, the improvement is real but less dramatic. CW
reception is improved with decreasing bandwidth more readily than SSB, so the operator
must determine whether using a wider bandwidth plus SSNR or simply narrowing the
bandwidth produces the most improvement. While CQing during a contest, wider bandwidths are needed to detect off-frequency callers and here SSNR improves results. When tuning around the band DXing or searching & pouncing, narrower bandwidths are useful and often provide better results. Different conditions demand different reactions. K4 operators now have new options and choices to make.

SSNR with FT Modes

Theoretically, SSNR should not improve the 50-Hz bandwidth FT mode reception. However, some operators have reported benefits. My experiments have shown mixed results, but these are likely statistically insignificant, within the error induced by propagation variation between receive cycles.

SSNR is the most effective noise reduction algorithm I’ve ever experienced—shockingly so. If you haven’t updated your K4 software, do so and give it a try. I am confident that you’ll be impressed.