[Elecraft] LP Pan versus P3 Panadapters

[Edward R. Cole]

I do not have a P3, so my comments are based on my experience using 
the SDR-IQ on 144-MHz using a 144/28 converter to receive 2m-eme signals.

The sensitivity of the display is tied to the sampling rate (FFT/BLK 
size on the control panel of the SDR-IQ).  With maximum sampling of 
262,144 I get a bin size of 0.42 Hz.  This also referred to as the 
RBW (resolution band width).  The narrower the FFT routine in the sw 
is, the more sensitive the display is.  It is analogous of using 
narrow filters to hear very weak signals.  But one cannot copy CW 
using bandwidths under 25-Hz due to filter "ringing" effect, so the 
panadapter display can be several times more sensitive than what one 
hears, depending on what the sw permits.

I usually run my SDR-IQ at 65,536 or 32,768 samples/sec with RBW of 
1.7 or 3.4 Hz.  WSJT sw that is used for eme has a RBW of 4.3 Hz (I 
believe) and that will display signals 10-dB weaker than can be 
heard.  WSJT has a max span of about 4-KHz.

 From what I am reading from those who are running the P3, RBW is 
dependent on span size.  This is true for the SDR-IQ, as well.  The 
figures I have quoted is for a span of 100-KHz.  If I expand to 
190-KHz then 262,144 produces a RBW=0.75 Hz.  So if the P3 is looking 
at the whole 20m band (350-KHz), for example, it will have less 
sensitivity than narrower spans.  I would guess that a panadaptor is 
used for different reasons on HF than it is for operations like eme; 
signals are not as weak as a rule.

I made sensitivity tests that were the subject of a paper at 
Microwave Update 2005 on the applicability of the SDR-IQ for eme.  I 
compared it to my FT-847.  I fed both radios with a signal generator 
able to generate down to -172 dBm and found that for a span of 
100-KHz the FT-847 with WSJT sw could see -152 dBm signals.  The 
SDR-IQ could see -166 dBm signals at the same span.

There were two preamps feeding both radios so this explains about 
30-dB of the overall sensitivity (the FT-847 is spec at -122 dBm 
SSB).  On air tests using real eme signals verified the results.  I 
hope this sheds some light on the topic, if only as background info.


73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-QRT*, 432-100w, 1296-QRT*, 3400-fall 2010
DUBUS Magazine USA Rep dubususa at hotmail.com
======================================
*temp