K3: Question about S-Meter Calibration

[Grant Youngman]

So, the S-Meter calibration instructions in the manual indicate that  
PRE should be on.  When calibration is done,  that means that a 50uV  
signal reads S-9 with PRE on .. but about S-7 with PRE off.  And then  
if the mode is changed from Normal to Absolute, a 50uV signal reads  
S-7 with or without the preamp.

Just wondering (maybe I need to RTFM and specs again), why that would  
be the case, vs. 50uV being S-9 without the preamp.  I have always  
just ignored the instruction manual, and calibrated to S-9 with the  
preamp off.  So a 50uV signal reads S-9 (with or without preamp  
engaged if the mode is Absolute).

Am I screwing something up?  Or does it just not matter all that much  
since (1) it doesn't impact anything other than the bar graph, (2) an  
S-meter reading is not all that terribly important anyway (I don't run  
a lab),  (3) it's all relative, (4) the P3 is in my future, and (5)  
all DX or contest exchanges are 5-9 by definition  :-)

To set the record straight on a related topic -- I posted about an  
issue with gain calibration using the updated K3UtilityOSX a couple of  
days ago.  Turned out it was apparently nothing more than cockpit  
error and fat-fingers on my part, which is typical.  Dave Fleming and  
Elecraft support (Gary Surrency) were both very helpful and got me set  
on the path of truth and light ...

Anyone have any insight on the S-meter cal thing?

Thanks ... Grant/NQ5T
K3 #2091 with most all the extras.
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[KK7P]

> So, the S-Meter calibration instructions in the manual indicate that  
> PRE should be on.  When calibration is done,  that means that a 50uV  
> signal reads S-9 with PRE on .. but about S-7 with PRE off.  And then  
> if the mode is changed from Normal to Absolute, a 50uV signal reads  
> S-7 with or without the preamp.

Yes.  In the end, you must calibrate the S Meter for how you use it. I
operate in ABS mode, so I have PRE OFF and ATT OFF when I do the S Meter
cal using a -73 dBm (50 uV) source.  I could leave PRE ON in thie mode,
but I know that the DSP is adding an offset when I do that (as it does
for ATT), so I calibrate with both OFF.

If I then go to the "other" S Meter mode, it is inaccurate, of course.

> Just wondering (maybe I need to RTFM and specs again), why that would  
> be the case, vs. 50uV being S-9 without the preamp.  I have always  
> just ignored the instruction manual, and calibrated to S-9 with the  
> preamp off.  So a 50uV signal reads S-9 (with or without preamp  
> engaged if the mode is Absolute).

Correct.

***

When you do the RF Gain Calibration procedure, it is important to know
that your signal source is -73 dBm (50 uV).  If you use the S Meter to
make this determination, you need to know how it was calibrated.


73,

Lyle KK7P

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[Don Wilhelm-4]

Grant,

Mine does the same thing as yours - it appears as though the S-meter
'abs' setting is the same as S-meter 'nor' with the preamp OFF.  So what
I did was calibrate the S-meter with the preamp OFF and then set it to
'abs'.
Makes sense to me, after all S-9 is supposed to be a 50 uV signal at the
antenna.

As an additional point - I had to do a lot of 'fiddlin' to get the
S-meter calibrated with the preamp on.  With the preamp off, my K3
S-meter parameters are set right at the default values.

73,
Don W3FPR

Grant Youngman wrote:

> So, the S-Meter calibration instructions in the manual indicate that  
> PRE should be on.  When calibration is done,  that means that a 50uV  
> signal reads S-9 with PRE on .. but about S-7 with PRE off.  And then  
> if the mode is changed from Normal to Absolute, a 50uV signal reads  
> S-7 with or without the preamp.
>
> Just wondering (maybe I need to RTFM and specs again), why that would  
> be the case, vs. 50uV being S-9 without the preamp.  I have always  
> just ignored the instruction manual, and calibrated to S-9 with the  
> preamp off.  So a 50uV signal reads S-9 (with or without preamp  
> engaged if the mode is Absolute).
>
> Am I screwing something up?  Or does it just not matter all that much  
> since (1) it doesn't impact anything other than the bar graph, (2) an  
> S-meter reading is not all that terribly important anyway (I don't run  
> a lab),  (3) it's all relative, (4) the P3 is in my future, and (5)  
> all DX or contest exchanges are 5-9 by definition  :-)
>
> To set the record straight on a related topic -- I posted about an  
> issue with gain calibration using the updated K3UtilityOSX a couple of  
> days ago.  Turned out it was apparently nothing more than cockpit  
> error and fat-fingers on my part, which is typical.  Dave Fleming and  
> Elecraft support (Gary Surrency) were both very helpful and got me set  
> on the path of truth and light ...
>
> Anyone have any insight on the S-meter cal thing?
>
> Thanks ... Grant/NQ5T
> K3 #2091 with most all the extras.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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[Gary, W7TEA]

Grant, on an earlier thread on this general topic Wayne said that
SMTR OF and SC may need further tweaking when switching to Abs
after first aligning in Nor mode with Pre on.   My experience mimics yours.
With a 50uv signal and the S meter at S9, Nor OF setting is 30 and Abs
setting is at 23.  So that's quite a tweak.

I prefer Abs, having gotten used to the idea with my Omni VII.  I'm not
sure why it is recommended that the alignment first occur in Nor mode
unless what you and I are seeing is abnormal.  It is almost as if the settings
are independent except for SC which is 14 in both cases. So, no insight,
just a similar experience.

Gary W7TEA
K3 #1001

<quote author="Grant Youngman">
So, the S-Meter calibration instructions in the manual indicate that  
PRE should be on.  When calibration is done,  that means that a 50uV  
signal reads S-9 with PRE on .. but about S-7 with PRE off.  And then  
if the mode is changed from Normal to Absolute, a 50uV signal reads  
S-7 with or without the preamp.

Just wondering (maybe I need to RTFM and specs again), why that would  
be the case, vs. 50uV being S-9 without the preamp.  I have always  
just ignored the instruction manual, and calibrated to S-9 with the  
preamp off.  So a 50uV signal reads S-9 (with or without preamp  
engaged if the mode is Absolute).

Am I screwing something up?  Or does it just not matter all that much  
since (1) it doesn't impact anything other than the bar graph, (2) an  
S-meter reading is not all that terribly important anyway (I don't run  
a lab),  (3) it's all relative, (4) the P3 is in my future, and (5)  
all DX or contest exchanges are 5-9 by definition  :-)

To set the record straight on a related topic -- I posted about an  
issue with gain calibration using the updated K3UtilityOSX a couple of  
days ago.  Turned out it was apparently nothing more than cockpit  
error and fat-fingers on my part, which is typical.  Dave Fleming and  
Elecraft support (Gary Surrency) were both very helpful and got me set  
on the path of truth and light ...

Anyone have any insight on the S-meter cal thing?

Thanks ... Grant/NQ5T
K3 #2091 with most all the extras.