[Elecraft] Interpretation of P3 display

[Fred Jensen]

On 6/8/2012 11:45 AM, Harold V wrote:
> I have a question for the group regarding interpretation of the P3 display of
> SSB signals.
>
> Primarily I use it to spot stations on quiet bands or spot openings on busy
> bands.  But I am trying to gain a better understanding of what it is showing me
> regarding the quality of signals as well.

I run mine at spans of 20 or 40 KHz [I have the PF keys set for those] 
when operating in contests or when I want to see the immediate band 
around me.  I use fixed-track all the time, so sometimes it's not "all 
around me," just on one side.  If I want to look at someone's signal 
spectrum, I go to a span of 6.  If he's really wide, I'll look at it at 
a span of 10 KHz.

> Is this what is known as "splatter"?  Is the station overdriving their
> transmitter or linear?  Is their ALC or compression too high?  Is the frequency
> response of their microphone too wide?

OK Van, multiple questions.  What most folks call splatter is caused by 
driving the last amplifier stage into saturation [i.e. it can't produce 
any more power so it clips off the peaks].  It doesn't really involve 
compression, they're just driving their amplifier into saturation, it 
clips the peaks [a very non-linear occurrence], and all sorts of IMD is 
generated around their signal.  The cure is, "Don't drive your amplifier 
into saturation."  This is sometimes called flat-topping.

Another problem could be phase noise.  This is generated inherently in 
the transmitter part of your radio, and is essentially unwanted random 
FM modulation of your signal caused by jitter in the frequency.  Phase 
noise on a signal will be essentially independent of the strength of the 
signal, within reason, although the guy down the block with 1.5 KW and 
lots of phase noise can easily take out the entire band for you when he 
taps his paddle.
>
> A good friend of mine has a K3/P3 and we have discussed this at length and come
> to the conclusion that we really don't understand what we are seeing.  Anyone on
> the list have comments as to what they have observed or an explanation of what
> we are seeing?

There are a whole lot of other causes.  Getting an amplifier and 
saturating the core in your balun can wreak havoc on the ham bands, and 
on your neighbor's TV's if they're receiving over the air.  Same effect 
as driving your amplifier to saturation.

Highly compressed audio can lead to unintelligibility on SSB.  It tends 
to be a bit wider, but the real problem is it totally fills the 
bandwidth with no dynamic range, something we depend on in our heads to 
understand speech.  ESSB signals will be broader, as will AM.

I've been watching WWV on 10 MHz.  I'm working on a project for my wife 
and I need to get the little PIC to keep time reasonably well.  At 4 KHz 
span, I'm surprised by the spectrum.  It *IS* WWV, I'm sure there's 
nothing wrong, but I still can't explain what I see.

Your P3 opens a whole different view of the radio spectrum.  It's worth 
exploring.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org