Topband: Hi Z amplifiers for 160m

[Jim Brown]

On 3/11/2020 9:39 PM, Michael Tope wrote:
> The signal components add coherently at the combiner output yielding a 
> total signal voltage of 14.14 Volts rms. The noise voltages are 
> incoherent, so they add as root-sum-square at the output of the 
> combiner. This yields a total noise voltage of sqrt(0.707^2 + 0.707^2) = 
> sqrt(1) = 1.0 Vrms. Thus, the combined noise voltage is unchanged, but 
> the signal voltage goes up by sqrt(2).

This is also why averaging in measurement systems and spectral displays 
improves their signal to noise ratio. As the number of averages is 
increased, signal to noise increases using the same math as above. I set 
averaging on my P3 to the max, the noise averages out, adjust the 
display reference level so that the noise is at the bottom of the 
display, causing even the weakest carriers (or CW) to be seen above the 
noise (and as faint traces in the waterfall).

We used averaging extensively in pro audio measurement systems, 
beginning with Time Delay Spectrometry around 1982. Which, by the way, 
was invented about ten years earlier by the late Richard Heyser, was was 
at JPL at the time. In this AES Paper, I buried a TDS sweep in a music 
track at a level that was nearly inaudible and fed it through a popular 
broadcast audio processor to study it's dynamic frequency response at 
high levels of compression. The sweep was nearly inaudible, the the 
system was able to recover it by 64X averaging, combined with TDS's 
inherent noise rejection.

http://k9yc.com/AESPaper-TDS.pdf

73, Jim K9YC