K3 IF/AF Dsp questions (comparisons)

[N2EY]

-----Original Message-----
From: [hidden email]

>I agree that 5 dB per S-unit makes good engineering sense.  Sorry to
the
>standards group, but 6 db per s-unit just doesn't add up.

Sure it does. 6 dB is four times the power. Half an S unit is doubling
the power.

5 dB per S-unit means two S units are ten times the power and four S
units are one hundred times the power.

>S-meters are only useless because they've been built that way for too
>many years.

IMHO that depends on whether you want a receiver or a lab-quality
selective voltmeter.

73 de Jim, N2EY
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[Darwin, Keith]

 
I've had a couple of off-list replies as well, providing good defense
for the 6 dB per s-unit standard.  Yes 6 dB is 4x the power but a linear
amp is usually 10x the power which is 10 dB or 2 s-units.  Also S9+10 dB
would be a nice even 2 S-units over S9 or the equivalent of S11.  If it
were 6 dB per unit, s9+10 would be something like S10.8  Yuck!

Anyway, whether it is 5 or 6 is less important than having it consistent
from S9 to S1 and I still say makers could easily do a better job of
producing a linear meter.  There is a lot of room for meters to be
better without having to be lab quality.  (Eric, hope it's not too late
for the K3).

- Keith N1AS -
- K2 5411.ssb.100 -

-----Original Message-----
>...but 6 db per s-unit just doesn't add up.

Sure it does. 6 dB is four times the power. Half an S unit is doubling
the power.

5 dB per S-unit means two S units are ten times the power and four S
units are one hundred times the power.

>S-meters are only useless because they've been built that way for too
>many years.

IMHO that depends on whether you want a receiver or a lab-quality
selective voltmeter.

73 de Jim, N2EY
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[Brian Lloyd-6]

On May 17, 2007, at 8:24 AM, Darwin, Keith wrote:

> producing a linear meter.  There is a lot of room for meters to be
> better without having to be lab quality.  (Eric, hope it's not too  
> late
> for the K3).

The beauty of a radio where all the display functions (including the  
S-meter) are managed by the housekeeping processor is that the  
programmer can easily include a table lookup to calibrate the meter  
display. Frankly, it would only increase the size of the code that  
implements the S-meter by 4-5 lines.

73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com


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[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
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[k6dgw]

Ken Kopp wrote:
> We Yanks have always resisted the "world order" when it comes to
> measurements ..... Lessee, the last I knew it was just us and Libya
> holding  out ...
>

Quite the contrary, Ken.  We Yanks are going metric all right ... inch
by inch.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2007 CQP Oct 6-7
- www.cqp.org
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[Don Wilhelm-3]

Kieth,

If -73 dBm is equal to S-9, then at 6 dB per S unit, S-0 would be -140
dBm - sounds about right to me for a modern receiver.

73,
Don W3FPR

Darwin, Keith wrote:
> I agree that 5 dB per S-unit makes good engineering sense.  Sorry to the
> standards group, but 6 db per s-unit just doesn't add up.  Having the
> S-meter at S-1.5 with the antenna disconnected?  Can we say useless?
>
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[Bill Coleman-2]

On May 17, 2007, at 11:49 AM, Vic K2VCO wrote:

> 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.

This is exactly what I do! My S5 is a bit higher, but, yeah, if  
there's any indication on the S-meter, you are S5, easy.

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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