P-3 background noise level interpretation

[Mike Scott-7]

I wonder if someone would check my understanding of interpreting broadband
noise on the P-3 display.

 

I have gone through the P-3 calibration procedure on 40M as well as
calibrating my S-Meter on the same band.

 

Now when looking at band noise I see the tops of the yellow line at around
the -110 dBm level. If I run peak-hold, the peaks are maybe -108 dBm in the
region where the K3 is tuned (between the MKR A cursor). Without further
interpretation this would indicate S-3 or so.

 

The K3 S-Meter shows S-6 to S-7, hmmm.

 

Should I be adding 10+log(K3 bandwidth/P3 resolution) to my P-3 view to
compare with K-3 S-Meter?

 

+/- 10 KHz span: P3 resolution = 20,000/450 = 44.4 Hz

K3 bandwidth = 2700 Hz (stock filter)

 

10*log(2700/44.4) = 17.8 dB

 

-110 dBm +17.8 dB = -92 dBm or around S-6.

 

 

AE6WA

Mike Scott

Tarzana, CA

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[Alan Bloom-2]

The effective bandwidth of the P3 is one pixel on the display.
(Somewhat more than that for spans < 5 kHz.)  Each pixel is about 1/450
of the span.

> +/- 10 KHz span: P3 resolution = 20,000/450 = 44.4 Hz
>
> K3 bandwidth = 2700 Hz (stock filter)
>
> 10*log(2700/44.4) = 17.8 dB

You got it right.  Assuming 6 dB per S-unit, about an 18 dB difference.

That's only for noise.  CW signals should show the same level on the P3
as on the K3.

Alan N1AL


On Fri, 2010-11-12 at 11:04 -0800, Mike Scott wrote:

> I wonder if someone would check my understanding of interpreting broadband
> noise on the P-3 display.
>
>  
>
> I have gone through the P-3 calibration procedure on 40M as well as
> calibrating my S-Meter on the same band.
>
>  
>
> Now when looking at band noise I see the tops of the yellow line at around
> the -110 dBm level. If I run peak-hold, the peaks are maybe -108 dBm in the
> region where the K3 is tuned (between the MKR A cursor). Without further
> interpretation this would indicate S-3 or so.
>
>  
>
> The K3 S-Meter shows S-6 to S-7, hmmm.
>
>  
>
> Should I be adding 10+log(K3 bandwidth/P3 resolution) to my P-3 view to
> compare with K-3 S-Meter?
>
>  
>
> +/- 10 KHz span: P3 resolution = 20,000/450 = 44.4 Hz
>
> K3 bandwidth = 2700 Hz (stock filter)
>
>  
>
> 10*log(2700/44.4) = 17.8 dB
>
>  
>
> -110 dBm +17.8 dB = -92 dBm or around S-6.
>
>  
>
>
>
> AE6WA
>
> Mike Scott
>
> Tarzana, CA
>
> ______________________________________________________________
> 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

______________________________________________________________
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