[Elecraft] K3s/P3 noise comparisons

[Jim Miller]

Alan

You nailed it!

Thanks!

jim ab3cv



On Sat, Apr 18, 2020 at 3:46 PM Alan Bloom <n1al at sonic.net> wrote:

> > Since noise power scales with the square root of the bandwidth
>
>
>
> That may be the source of the error.  Noise power scales directly with the
> bandwidth.  (Noise *voltage* scales as the square root of the bandwidth.)
>
>
> Since the P3's effective bandwidth is 11 Hz and the K3 sensitivity is
> specified for 500 Hz, the P3 should be showing
>
> 10 * log (500/11) = 16.5 dB lower than the P3.
>
>
> If the P3 is reading -162 dBm, then that corresponds to -145.5 dBm on the
> K3, close to the -145 dBm spec.
>
>
> Alan N1AL
>
>
>
> On 2020-04-18 12:33, Jim Miller wrote:
>
> I'm doing some work on measuring RFI levels on 6m at my QTH.
>
> One tool I'm using is the P3 with averaging set to 20 to make for easier
> reading.
>
> With the K3s preamp 2 engaged I read -162dbm on the P3 scale when connected
> to a 50ohm dummy load.
>
> I'm trying to correlate that to the MDS numbers for the K3s.
>
> The K3s specification with Pre2 engaged is -145dbm measured in a 500hz
> bandwidth.
>
> The effective bandwidth of the P3 per the P3 manual is Scale/450 which for
> 5K that I'm using is 11hz.
>
> Since noise power scales with the square root of the bandwidth that
> should result in a ratio of SQRT(45) or 6.7. 10*log(6.7) = 8.2
>
> Adding -162 to 8.2 only brings me to -153db.
>
> So it seems I'm missing something. The P3 is telling me the K3s is 8db more
> sensitive than its specification.
>
> What am I missing?
>
> Thanks
>
> JIm ab3cv
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