On Jul 29, 2011, at 10:37 AM, Mike Harris wrote:
> What advantage is gained from the XY scope that isn't available from a
> waterfall display from the point of view of signal tuning?
You can see many RTTY characteristics with just a single tuning tool, and as a
tuning tool (with an analog scope), it is very, very fast.
You can easily notice selective fading (one ellipse shrinking relative to the
other, sometimes in the blink of an eye). You can also see multipath (when one
ellipse is large while the second ellipse does not completely vanish at the
same moment). Most waterfalls will not catch fast selective fades, and
waterfalls are practically useless to determine if there is multipath. You can
use that information to quickly pick some post-processing steps in your modem
that optimizes for selective fading or for multipath.
IMHO, waterfalls are better, of course if you use mouse clicks to tune. Cross
ellipses are better if you use the VFO knob to tune.
However, for fast *fine* tuning, a cross banana is still better than the
waterfall. cocoaModem lets you tune with a mouse click in a waterfall, but it
also displays a crossed ellipse for you to fine tune with the mouse scroll
wheel (or the Griffin PowerMate).
For signals that have poor SNR, being able to get within 10 Hz is often
helpful. cocoaModem's waterfall has a resolution of 2.7 Hz per pixel on the
screen (your mileage may vary with the modem that you use). It is much easier
to get better fine tuning with the crossed bananas than by staring at a noisy
waterfall.
Do not base how good or bad a cross ellipse display is by what you see from a
software modem. Their implementation quality varies. Get a good analog scope
that is fed with some analog filters. ... then, attempt to emulate that
response with software. I will even wager money that some software modem
developers (the ones W6WRT calls lazy :-) have never used an analog crossed
ellipse display in real life (and I am a cheap skate when money is concerned;
no linear amplifiers, no commercial beam antennas).
73
Chen, W7AY
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|