[Elecraft] LP Pan versus P3 Panadapters

[samuel ernst-fortin]

It strikes me, when implementing algorithms to compute Periodograms using 
DFT/FFTs, there are tradeoffs in variance and spectral resolution. There are a 
number of factors, including window/FFT length, window function,  amount of 
window overlap, degree of zero-padding, number of estimates  to average, choice 
of normalization factors, etc. Then you've got a lot  of considerations with 
respect to how that spectrogram is displayed on  screen that can influence the 
visual detection problem. We haven't even  addressed computational complexity / 
speed of computation. 


I do  not know how much flexibility the P3 allows for changing a number of  
these parameters, the manual indicates spectral resolution is changed with 
"span", so if everything is automatically selected for the end-user at this  
release of the software, perhaps  some configuration options might be placed 
back into the hands of the user in a subsequent release, including a  guide 
provided to help one understand these tradeoffs in PSD estimation and 
presentation and how to  configure the display for optimal results depending on 
what you want to do. The manual is not very verbose in this regard.

With sampling rate known, and these other parameters chosen, conceptually, the 
software  can report an estimate of the spectral resolution which could be 
theoretically  expected on a popup information window or other.

This is one argument for having an "external",  potentially more "open to 
adjustment" system for analysis of the IF  information, rather than say a P3.

KJ4VPI


________________________________
From: Alan Bloom <n1al at cds1.net>
To: Larry K1UO <k1uo at uninet.net>
Cc: elecraft at mailman.qth.net
Sent: Tue, September 14, 2010 1:00:30 PM
Subject: Re: [Elecraft] LP Pan versus P3 Panadapters

Hi Larry,

It depends on the span.  Unlike some other panadapters, the P3
automatically reduces the sample rate as you narrow the span, which
improves the sensitivity.

For example, I have my HP8656B signal generator set to 3640 kHz with the
amplitude as low as it will go (-127 dBm).  The K3 has the preamp off,
the attenuator on, and default CW shift and width.  Under those
conditions I can just barely hear the carrier.  It's weak enough that if
it were a modulated CW signal I don't think I could copy it.

However the carrier is clearly visible on the waterfall if I set the P3
span to 2 kHz.  As I increase the span the signal gradually gets harder
and harder to see.  Above about 30 kHz or so the signal disappears into
the noise.

So that's the trick.  Narrow the span to make those signals pop out of
the noise.

73,

Alan N1AL


On Tue, 2010-09-14 at 06:03 -0700, Larry K1UO wrote:
> Bill,
> 
>    I can tell you that just last night, on 160 meters, I copied 2 very weak
> stations perfectly Q5 that did not show on the P3 waterfall.  Now, Its
> entirely possible its my adjustment skills but I dont think so.  Yes..the K3
> IF Mod was factory installed.     This has happened more than once.  For
> some reason I was expecting the P3 to show these very weak signals better
> than I could find them myself while tuning but no amount of adjustment so
> far will do this.  I may be expecting too much?
> Just so you know what anothers experience has been so far.
> 73
> 
> 
> 
> 
>   I too would like to see details of the improvement over LPan etc. I am a
> long time user of SDR/computer panadapters for use in detecting very weak
> signals at UHF/VHF/microwave. I use a Softrock on the K3 IF port since I got
> my K3 a year ago.  I have yet to see one report regarding weak sig detection
> with the P3 after many requests to the initial testers of the P3. ANYONE out
> there looking for weak weak sigs with a P3??
> 
> 73  Bill K0AWU  EN37ed
> 
> 


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