[Elecraft] OT - WSJT-X & K3s

[Jim Brown]

On 9/5/2017 1:21 PM, Joe Subich, W4TV wrote:
>
> You will find almost without fail, the common emitter transistor
> preamp with unbypassed emitter bias resistor is, in fact, clipping well
> below 1V.

Gee, I said 100 mV, which is 20 dB below 1 V.

> Remember, we're talking about *AMATEUR* equipment - not professional
> and broadcast equipment with its 1V or 4V P-P standard "Line" levels
> and wide range mic preamps that provided standard level outputs

I am well aware of the differences -- that was my profession for 50 
years, and, among other things, I'm still on the AES Standards 
Committee, which standardizes stuff like this!  Indeed, consumer line 
inputs (into which ham gear falls) typically clip around 1V. Nowadays, 
pro line level equipment clips in the range of +18 to +24 dBu. That's a 
lot more than 4V P-P.

> In any case, a typical dynamic microphone - professional or amateur -
> is rated around -55 dBV/Pascal (check Shure, EV, etc.) some may be a
> more sensitive, some less.  For those who do not know, 1 Pascal is a
> 94 dB Sound Pressure Level (think traffic on a busy roadway) - nearly
> 25 dB above the EPA threshold for hearing protection!  -55dBV is in
> *the millivolt range*.  5 mV is a decent level for normal conversation
> with a dynamic microphone within 6" of the lips.

I suggest that you drag out a scope and look at the output of some these 
mics with speech with different people and different working distances. 
The variables are distance and how loud the speech is. I know guys who 
get pretty excited calling DX or during a contest. And sound pressure 
level follows inverse square law, just like antennas. That means the 
voltage doubles (+6dB) every time the distance between mic and mouth 
drops by a factor of 2.  1-in to 2-in is 6 dB. 2-in to 4-in is 6 dB. 
4-in to 8-in is 6 dB. And having ridden gain on a wide variety of 
performers for 50 years, I can assure you that it is VERY common for 
speech levels to vary by 20 dB in perfectly ordinary speech.
>
> All of this information is available from public sources and a little
> study.

I learned it more than 50 years ago. :)

73, Jim K9YC