[Elecraft] K3 S-Meter and Noise

[Don Rasmussen]

Here's my look for what its worth. ;-)

I have been following AGC, S-meter, and threshold/slope values since the beginning - K2 #272 over two years ago. 

Until recently, I have found that K3 sensitivity varied between serial numbers and that could not be changed. I suspect this value was not measured before units left the factory. I had about 10db difference between K3 #272 and #2308.

The s-meter presentation was tied to that difference. A hotter receiver would have a higher resting value on a given band that the more moderate receiver. 

Happily, in the newest limited beta release this has been addressed. The RF Gain can be calibrated to the user's satisfaction. It works great. For example - tonight on 40m I see the same resting band noise that I'd see on IC756p, or OMNI VI+. It is S3.

In the past, the K3 always showed at least 2 points higher, sometimes 3, assuming identical sensitivity with my other sets. So, in the past my K3 would be showing S6 as resting. That was troublesome because I could not see how strong anyone was, if it were less than S6.

At my location the single biggest plus with my K3's was getting the updated DSP board. That took all the critical adjustment out of THRESHOLD and SLOPE in CONFIG and made the default values good everywhere for me. The next major upgrade was this latest firmware and DSP that the guys have been working on. It allows RF Gain calibration. Very nice indeed.

I did write custom s-meter code so that when the first bar on the K3 is solid and the next one is flickering, I can actually see on my remote meter the precision of the value as it is swinging up from S1 and down from S2. For the most part I find flickering bars to be useless. ;-)

Cheers,
Don 







[Elecraft] [K3] RE: K3 S-Meter and Noise

Don Wilhelm w3fpr at embarqmail.com 
Sun Oct 4 19:43:06 EDT 2009
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Jim,

There are 2 reasons I can think of to make that condition 'normal'.
First is if you have the preamp on for a band where it is not needed - 
that would amplify the atmospheric noise when the receiver has no signal 
present and no AGC is active.  If your preamp is on, try tuning it off 
and see if it makes a difference.  A good test for whether the preamp is 
needed or not is to disconnect the antenna and reconnect it.  If the 
noise level increases when you connect the antenna, there is more than 
enough gain in the receiver - turn off the preamp and try the same thing 
again - if the noise level still increases when the antenna is 
connected, try again but use the attenuator this time.
If you can just barely hear the band noise, that is the proper gain 
setting for that band at that time and your antennas.  The noise level 
on a particular band will vary, perhaps even on an hourly basis (i.e. 80 
meters is noisy during the day, but will quiet down some at night).