[Elecraft] PX3 Amplitude calibration

[Cady, Fred]

I think Alan, NA1L, posted some words similar to these to the reflector some time ago about why the PX3 and KX3 signal strengths don't agree at times.  They probably apply to your question.

1.	The PX3's LvL Mode is dBm.  The dBm display is a quantitative display of power (in decibels relative to a milliwatt) at the KX3's antenna.  That signal has an absolute power and thus isn't, nor should it be, affected by the KX3's signal processing preamplifier or attenuator.  Therefore, the PX3 automatically compensates for the KX3's preamplifier or attenuator when the display is dBm.  Changing the preamplifier and attenuator will not change the signal displayed on the PX3.
Meanwhile, if  the KX3's SMTR MD menu is nor, changing the preamplifier and attenuator will change the signal displayed on the KX3.   

2.	The PX3's LvL Mode is S-units.  When the PX3 shows S-units, it has the same behavior as the KX3's S-meter and increases when the preamplifier is on and decreases when the attenuator is on.  Note that for most bands the preamplifier must be set at +20 dB for a 50 microvolt signal to display S9.

3.	The signal level on the KX3 and PX3 depends on their respective effective bandwidths.  In the KX3 the bandwidth is set by the pass band tuning control (PBT I/II).  In the KX3 the S-meter gives you a measure of the signal within the KX3 bandwidth.  In the PX3 the effective bandwidth is approximately the span divided by 450 (there are 450 pixels  displaying signals across the PX3 display).  In the PX3 each pixel gives you a measure of the signal within the effective bandwidth of the pixel.  If the two bandwidths are different, the KX3 and PX3 signal displays will be different.  
This will particularly be evident with wideband signals such as SSB.  Even when the PX3 span is 200 kHz its effective bandwidth per pixel is 440 Hz and it does not contain the full signal that is seen on the KX3 S-meter.

I agree with Phil.  In essence each display serves a different purpose.  The KX3 S-meter shows you the signal strength of the one signal within its passband and the PX3 shows you the relative strengths of a number of signals shown in its span.  

Cheers all,
Fred KE7X

Author of:
"The Elecraft K3: Design, Configuration and Operation 2nd ed"
"The Elecraft KX3 - Going for the summit"
"The Elecraft KPA500 and KAT500 - the K-Line Dream Station"
Printed, coil bound copies of these are all available at www.elecraft.com
KPA500 and KAT500 Quick Set Up Guide
http://www.ke7x.com/home/k-line-introduction-and-set-up-guide
KAT500 and KXPA500 Tuner Operation
http://www.ke7x.com/home/kat500-and-kxpa100-tuners


> -----Original Message-----
> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
> Phil Wheeler
> Sent: Thursday, February 05, 2015 9:06 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] PX3 Amplitude calibration
> 
> Same here, but I really don't care. I don't use panadapters to measure
> signal strength but to look at the band.
> 
> 73, Phil W7OX
> 
> On 2/5/15 7:02 AM, dmb at lightstream.net wrote:
> > With the same Span settings, my PX3 consistently indicates signal and
> > noise floor levels about 10 dBm higher than my P3 (or a number of
> > other panadapters on SDR radios).
> >
> > I've looked through the manual, and see that there is an amplitude
> > calibration for transverters using MENU:XV Gain. However, I see no
> way
> > to calibrate the level for non-transverter use.
> >
> > The P3 has a menu option: Lvl Cal for this purpose, but from what I
> > can see there is no parallel for the PX3.
> >
> > Am I overlooking something?
> >
> > tnx and 73,
> >
> > Dale
> > WA8SRA
> 
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