Elecraft

P3 Vs. K3 Noise Level

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Brian J. Linn

P3 Vs. K3 Noise Level

All:

Even after considering the P3 manual (page 21) and with AGC off, I find the
following difference in S unit measurement odd.

Band P3 K3

75m S5 S9

10m S0 S2

I'm trying to ascertain an accurate noise level reading at my QTH. Does
anyone have any thoughts on the degree of difference in these readings?

Brian KD0HII

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Alan Bloom

Re: P3 Vs. K3 Noise Level

The indicated noise level depends on the receive bandwidth. For
example, if you use a narrower bandwidth on the K3, you'll notice that
the S meter reads lower.

The effective bandwidth of the P3 is approximately one pixel on the
display, which is SPAN/468. So, for example, if the span is 47 kHz, the
effective bandwidth is about 100 Hz. If the K3 bandwidth is 2.7 kHz,
then the P3 should read 10 * log (2700/100) = 14 dB lower than the K3.
14 dB is roughly 3 S-units.

When measuring a steady carrier, the K3 and P3 should read the same,
since all of the signal is within the bandwidth. The P3's amplitude can
be calibrated with the "Lvl Cal" menu selection.

Alan N1AL

On 03/07/2016 03:14 AM, Brian J. Linn wrote:

> All:
>
>
>
> Even after considering the P3 manual (page 21) and with AGC off, I find the
> following difference in S unit measurement odd.
>
>
>
>
>
> Band P3 K3
>
> 75m S5 S9
>
> 10m S0 S2
>
>
>
>
>
> I'm trying to ascertain an accurate noise level reading at my QTH. Does
> anyone have any thoughts on the degree of difference in these readings?
>
>
>
> Brian KD0HII
>
>
>
>
>
> ______________________________________________________________
> 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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NK7Z

Re: P3 Vs. K3 Noise Level

Alan,
Thank you for such a clear explanation! I understood the process, and
why, but having someone actually put numbers to it helps in getting
that "gut feeling" as to why... Thank you!!
--
73's, and thanks,
Dave (NK7Z)

For software/hardware reviews see:
http://www.nk7z.net

For MixW support see:
https://groups.yahoo.com/neo/groups/mixw/info

For SSTV help see:
http://groups.yahoo.com/neo/groups/MM-SSTV/info

On Mon, 2016-03-07 at 09:56 -0800, Alan wrote:

> The indicated noise level depends on the receive bandwidth.  For
> example, if you use a narrower bandwidth on the K3, you'll notice
> that
> the S meter reads lower.
>
> The effective bandwidth of the P3 is approximately one pixel on the
> display, which is SPAN/468.  So, for example, if the span is 47 kHz,
> the
> effective bandwidth is about 100 Hz.  If the K3 bandwidth is 2.7
> kHz,
> then the P3 should read 10 * log (2700/100) = 14 dB lower than the
> K3.
> 14 dB is roughly 3 S-units.
>
> When measuring a steady carrier, the K3 and P3 should read the same,
> since all of the signal is within the bandwidth.  The P3's amplitude
> can
> be calibrated with the "Lvl Cal" menu selection.
>
> Alan N1AL
>
>
> On 03/07/2016 03:14 AM, Brian J. Linn wrote:
> > All:
> >
> >
> >
> > Even after considering the P3 manual (page 21) and with AGC off, I
> > find the
> > following difference in S unit measurement odd.
> >
> >
> >
> >
> >
> > Band  P3    K3
> >
> > 75m   S5    S9
> >
> > 10m   S0    S2
> >
> >
> >
> >
> >
> > I'm trying to ascertain an accurate noise level reading at my
> > QTH.  Does
> > anyone have any thoughts on the degree of difference in these
> > readings?
> >
> >
> >
> > Brian KD0HII
> >
> >
> >
> >
> >
> > ______________________________________________________________
> > 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]
> >
> ______________________________________________________________
> 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]