[Elecraft] Noise blanker and APF test recording

[Wayne Burdick]

A brief K4 audio sample can be downloaded using the link at the end of this email. 

This recording hows how the new K4 noise blanker algorithm can reveal a signal buried under loud noise. It also highlights the effectiveness of the audio-peaking filter (APF) when listening to a very weak CW signal. 

This was recorded on 17 meters, CW mode, in a 1 kHz bandwidth. Both receivers are turned on, tuned to the same frequency, and the recording is stereo. There's a slight delay between main and sub RX audio as the settings change; this is due to tapping A>B to copy the main RX NB and APF settings to the sub RX.

Things to listen for (T in seconds):

T0:    S-9 noise masking very weak carrier

T7:    Noise blanker turned on so that only atmospheric noise remains; carrier now barely audible

T14:   APF turned on, 30 Hz BW; carrier clearly audible

T23:   Carrier disappears, leaving band noise only

http://ftp.elecraft.com/K4/K4_audio_samples/K4%20NB%20demo%201.mp3

73,
Wayne
N6KR