[Elecraft] LP Pan versus P3 Panadapters

[Alan Bloom]

> Also, the waterfall (or Panafall) display should be used to
> take advantage of the averaging, which reduces random noise.

That's a point I forgot to mention.  If you turn on averaging in the
waterfall you can see farther down into the noise.  It works best on
steady carriers.  With CW signals you have to keep the averaging time
less than a dit.

On the P3, you turn on waterfall averaging with the "Wfall Avg" menu
selection.

Alan N1AL


On Tue, 2010-09-14 at 23:03 -0700, N8LP wrote:
> That's useful info for comparison, Alan. 
> 
> To satisfy my curiosity and answer the original question, I just ran a
> similar test with my LP-PAN, with and w/o the upcoming preamp mod kit.
> First, I should mention a couple differences in PowerSDR/IF and the P3. With
> PowerSDR/IF the sampling rate is fixed to one of three values... 48kHz,
> 96kHz or 192 kHz. The sensitivity of the display is the same at any span for
> any given sample rate. The sensitivity is proportional to sampling rate, so
> it is 3dB better at 48kHz than it is at 96 kHz, and 3dB better at 96kHz than
> it is at 192 kHz. My tests were run with the popular E-MU 0202 sound card
> (the E-MU 1212m is a few dB quieter).
> 
> With the K3 preamp ON, the stock LP-PAN at 96kHz sampling rate (and 96kHz
> span) produces a blip on the pan display 10dB above the noise floor with an
> input signal of -128dBm (noise floor of -138dBm). With the LP-PAN preamp kit
> installed, the sensitivity improves by 7dB (noise floor of -145dBm). Dynamic
> range remains the same. Remember, the noise floor will be 3dB better if
> 48kHz sampling rate is selected, and 3dB worse if 192kHz sampling rate is
> selected. 
> 
> For any weak signal work, the K3 preamp should be ON to overcome the loss of
> the K3 buffer. Also, the waterfall (or Panafall) display should be used to
> take advantage of the averaging, which reduces random noise. With
> PowerSDR/IF waterfall, I am able to clearly see signals within a couple dB
> of the noise floor, and which I can barely detect in the K3 by ear.
> 
> Also, remember that if you feed LP-PAN from the P3, there is an additional
> 3dB loss in the splitter. I have designed the LP-PAN preamp to provide a
> noise figure a few dB better than would normally be necessary, in order to
> compensate for the loss of the P3 splitter. The NF of LP-PAN w/preamp kit is
> about 6-7dB. 
> 
> Larry N8LP 
> 
>  
> 
> 
> 
> With the K3 preamp turned on I can see a -135 dB signal, even at 200 kHz
> span.  (I had to use a 10 dB attenuator to get the signal generator to
> go that low.)
> 
> Alan N1AL
>