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K3s/P3 noise comparisons

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Jim AB3CV

K3s/P3 noise comparisons

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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Alan Bloom

Re: K3s/P3 noise comparisons

> 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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Help: http://mailman.qth.net/mmfaq.htm
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Jim AB3CV

Re: K3s/P3 noise comparisons

Alan

You nailed it!

Thanks!

jim ab3cv

On Sat, Apr 18, 2020 at 3:46 PM Alan Bloom <[hidden email]> 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
>