K3 S meter

[Barry Simpson]

This is a subject which has been referred to in several recent postings.

 

The S meter in my K3 reads typically S5 as a minimum on SSB and S3 on CW
(selectivity 400Hz) on band noise, that is in the absence of a signal. When
disconnecting the antenna the S meter reverts to no reading.

 

It is a fact that the band noise is not for example  S5 - and my FT1000MP
MKV and TS2000 read S0 or S1 in the same situation.

 

In my view the K3 S meter is simply far too sensitive at the lower end. I
can make it read S1 on band noise by fiddling with the various settings.
However this then means that an S9 signal will read S5 or somesuch low
reading. A friend of my who lives nearby has a similar situation with his S
meter and I suspect it is typical of the K3 generally.

 

Wayne/ Eric please can you look into a fix for the next firmware update.

 

Barry Simpson  VK2BJ

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[dj7mgq]

> In my view the K3 S meter is simply far too sensitive at the lower end.

I do not think so. Some band/antenna/QTH combinations will on a *good*  
S-Meter show fairly high S values for band noise. Without wanting to  
reopen the S-Meter mail wars of from the days after the announcement  
of the K3. There is a norm: IARU Region 1 Technical Recommendation  
R.1. Ninety-nine percent of all S-Meters are *not good* i.e. are not  
in accordance with the norm.

<http://en.wikipedia.org/wiki/S_meter>

<http://www.iaru-r1.org/VHF_Handbook_V5_21.pdf>, Page 151
=====================================================================
1. One S-unit corresponds to a signal level difference of 6 dB,

2. On the bands below 30 MHz a meter deviation of S-9 corresponds
to an available power of -73 dBm from a continuous wave signal
generator connected to the receiver input terminals,

3. On the bands above 30 MHz this available power shall be -93 dBm,

s4. The metering system shall be based on quasi-peak detection
with an attack time of 10 msec ? 2 msec and a decay time constant
of at least 500 msec.
=====================================================================


vy 73 de toby

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[Bill W4ZV]

Barry Simpson wrote

It is a fact that the band noise is not for example  S5 - and my FT1000MP
MKV and TS2000 read S0 or S1 in the same situation.

This is because most rigs' meters are inaccurate and indicate ~3 dB per S-unit below S9.  Identical "S1" noise on another rig would be 24 dB (8 units [S9-S1] times 3 dB per unit) lower than 50 uV (S9), and indicate S5 on the K3 (4 units [S9-S5] times 6 dB per unit).  

Below is a typical S-meter (FT-1000), and you can see that "S1" on it is actually closer to a real S4:
(from http://www.n6rk.com click on "FT-1000 S-meter calibration"

Actual  Equivalent*
1   3.8
2   4.2
3   4.3
4   4.7
5   5.2
6   5.7
7   6.3
8   7.3
9   8.3

* Equivalent means S9 for 50 uV and 6 dB per S-unit, according to the following table on the same site as above:
http://www.n6rk.com  click on "Definition of S-unit"  

Another problem is that most rigs' S-meter readings will change if you are use a Preamp or Attenuator.  In the K3's ABSolute S-meter mode, the reading will not change with Preamp or Attenuator settings, since it is correctly reporting the signal at the input terminals (which of course does not change with the internal Preamp or Attenuator setting).

The K3 meter is probably one of the more accurate S-meters available, especially below S9.

73,  Bill