[Elecraft] [P3] How to measure bandwidth of RX signal

[David Cole]

Jim,

Thank you for the extended explanation, it helps!  I want to be sure I
understand the rig, the Panadaptor,  and how they interrelate.  THank
you again!

-- 
Thanks and 73's,
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On Mon, 2014-04-28 at 09:27 -0700, Jim Brown wrote:
> On 4/28/2014 8:37 AM, Vic Rosenthal K2VCO wrote:
> > What should work is to use the spectrum display of the P3. If you want 
> > to know, for example, the bandwidth of a signal at 30 dB down, you 
> > just find the points where the 'skirts' of the signal are 30 dB below 
> > the peak. This is easy to do on the P3 which can display the signal 
> > strength in dBm. 
> 
> Yes. And as N1AL recommends, use peak hold. I've done spectrum plots of 
> various signals and conditions with the P3. I usually set the SCALE for 
> a pretty wide range (like 72 or the full dB), and set the SPAN to about 
> 10 kHz. I use both the Peak Hold Mode and the Average Mode. In both 
> modes, but especially with Peak Hold, we must take care to differentiate 
> sidebands from other stations. I try to set the reference level so that 
> the peak of the signal is at one of the level lines and the noise level 
> is near the bottom of the display.
> 
> With almost any rig, you'll see small signals down the sides of the 
> slope that are intermod products, and they are usually symmetrical on a 
> CW or RTTY signal. A clean SSB signal should be well confined by the 
> bandpass filter limits of the audio and TX filter skirts. Anything that 
> extends beyond that is IMD. When a rig is badly overdriven, it's common 
> to see splatter as horizontal streaks extending above and below the 
> signal frequency.
> 
> Last week, I was on 20M SSB trying to work a weak DX station, but what I 
> heard was massive splatter from a QSO about 5 kHz up the band. One guy 
> was relatively clean, but the other was not. I broke the QSO to tell him 
> he was clobbering a weak DX station. Turns out he was an aeronautical 
> mobile using whatever radio was onboard. He didn't know whether he was 
> transmitting AM or SSB, but thought it was AM. I assured him that it 
> was, indeed, USB, and that the problem was that he was likely 
> overdriving it badly. He went QRT to figure it out.
> 
> As a percentage of transmitted signals, I don't find contesters any 
> better or worse than non-contesters -- we contesters stand out because 
> during a contest, there are a LOT more of us. :)  I'm retired, so I have 
> access to the ham bands during the day (when I'm not working on 
> something else). It's not at all uncommon to tune around 30, 40, and 80 
> during a weekday and hear fewer than a half dozen signals on these bands 
> (if you hear any at all), and no more than a few dozen on most of the 
> higher bands. Compare that to a major contest, when there are several 
> hundred workable signals on every band from any given location for the 
> duration of the contest, and for stations with better antennas, perhaps 
> 2-4X that number. The winners of contests like the ARRL SSB Sweepstakes 
> make more than 2,000 QSOs, and you can work a station only once.
> 
> 73, Jim K9YC
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