[Elecraft] P3 level accuracy

[Joe Subich, W4TV]

Don,

 > 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).

The primary point was not the K3 calibration (other than the IF gain
had been calibrated using the XG-2 and K3 Utility) but rather that
my particular XG-2 shows -70 dBm on the P3 vs. the -78 to -80 dBm
being claimed as "normal."  In addition, since the 1 uV signal shows
-105 dBm (vs. a calculated -107 dBm) it would tend to indicate the
gain slope is accurate and the overall gain within 3 dB (reasonable
accuracy considering that the XG-2 is not a calibrated standard).

I did calibrate the S meter on my K3 so the S9 reference was
"centered" (that is, I adjusted SMTR OF to the center of the
range - between the point the S9 bar just comes on and where
the S9+5 dB just comes on).  That should make my S9 bar indicate
-73 dBm +/-2.5 dB (-75.5 dBm to -70.5 dBm).

73,

    ... Joe, W4TV


On 9/27/2010 6:10 PM, Don Wilhelm wrote:
> 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
>>
>