[Elecraft] P3 level accuracy

[Don Wilhelm]

  Joe,

Comparing the K3 S-meter with the P3 amplitude indication has some 
limitations.

You stated that your K3 has been calibrated with the XG2 and I have no 
reason to doubt that, but do realize the granularity in that calibration.
If you calibrate the K3 S-9 indicator bar to just barely come on at -73 
dBm, and it will be the only bar illuminated until the signal goes up to 
-67 dBm (assuming 6 dB per S-unit).  So your indication is well within 
that granular step.  OTOH, if you calibrated the K3 S-meter so the S-9 
indication  is on full at -73 dBm, then your K3's S-9 could be as low as 
-79 dBm.
When comparing the K3 S-meter reading to the P3, one must consider this 
granularity in the K3 S-meter - in other words, it is not an "exact 
science" - allow for a +/- 6 dB range when making comparisons unless you 
have calibrated the K3 S-meter with this granularity in mind and can 
define the S-9 range more closely with accuracy.

I believe Alan is working on additional calibration processes for the 
P3, so if we could give this subject a bit of a rest until he completes 
that work, we will keep the reflector more quiet for now - after the P3 
calibrations are in place, then I am certain comments on accuracies and 
inaccuracies of the response will be well received and appreciated.

What we have currently is a digital display with its digital granularity 
being compared to an analog display with greater resolution than the 
digital display - to me, that is like comparing apples and oranges 
unless the granularity (and its consequences) is understood.  Those of 
us old-timers who grew up in the analog meter world do have a difficult 
time with this fact - it just does not seem "natural" unless we have 
gone through the "digital indoctrination" and learned its consequences.

73,
Don W3FPR

On 9/27/2010 5:26 PM, Joe Subich, W4TV wrote:
>
>   >  I've had several replies, all report the XG-2's -73dBm level to be
>   >  between about -78dBm and -80dBm on the P3, so it's at least
>   >  consistent, and will, no doubt receive Elecraft's attention in
>   >  due course!
>
> Well, my XG-2 shows up at -68 to -70 dBm on my P3.  The P3 shows
> a no signal noise floor of -150dBm (RX Ant) in a 2 KHz span.  The
> K3 has been calibrated to this same XG-2 using the K3 Utility and
> reads S9.  The 1 uV output shows up at -105dBm with the same test
> conditions.
>
> The K3 has the IF output modification fitted.
>
> 73,
>
>      ... Joe, W4TV
>