[Elecraft] K3 IF/AF Dsp questions (comparisons)

[Vic K2VCO]

Jim Brown wrote:

> Everyone except the receiver (and transceiver) manufacturers. If you
> run a curve of S-meter reading vs input voltage using a calibrated
> generator, you will find that it's close to 6dB/S-unit around S9, but
> close to 3 dB/S-unit when you get below S6 or S7. And I'm not talking
> about "junk" receivers -- I've done this with some very good radios,
> like TS850's and FT1000MP's.  No, I haven't done it with my K2's.
> Someday.

It's funny how excited people seem to get about one of the least 
important receiver accessories, the S-meter!

First of all, the number of dBm that equals S9 is not important. Why? 
Because the power that arrives at the antenna terminals of the receiver 
varies widely depending on antennas and propagation. An exact 
calibration might be useful during alignment of the receiver, but not 
during operation.

What *is* useful is the dB/S-unit calibration. And as Jim says, not only 
does this vary all over the map from receiver to receiver, but most 
meters are wildly inconsistent at different levels, probably because the 
manufacturer did not bother to build in an actual measurement circuit, 
but caught a ride on something designed for an entirely different 
purpose, like AGC.

A meter with consistent units would be useful for antenna comparisons, 
etc. Even that's hard, since 'interesting' signals often QSB enough to 
make comparison difficult. But I doubt that it would help much for 
signal reports.

I operate CW with little AGC action (RF gain turned down) so I get a 
sense of how strong the signal is by ear. I am often surprised that I 
don't agree with my meter. I seem to give reports like this:

S9 -- above S9 on my meter
S8 -- S7-S9 on my meter
S7 -- S4-S6 on my meter
S6 -- S3 on my meter
S5 -- No deflection to S1 on my meter
S4 -- No deflection, but above noise level
S3 -- No deflection, in and out of noise
S2 -- No deflection, mostly in noise
S1 -- I know you're there, but too weak to get more than occasional letters.

Of course the noise level varies!
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco