Posted by
John Ragle on
Apr 14, 2011; 8:14am
URL: http://elecraft.85.s1.nabble.com/XG3-device-tp6271930.html
The more I have glanced through the specs for this device, the more
puzzled I have become. I grew up on signal generators that put out a
(good approximation to a) sine wave. This device is described as an RF
"square wave" generator, which I take to mean that the output wave shape
is a trapezoid with very fast rise and fall times. As everyone knows,
the harmonic content of an ideal square wave falls off as 1/N. In other
words, this device is a harmonic generator, par excellence, very rich in
harmonic content. To get a sine wave, one has to run it through a
bandpass filter. In this case, the bandpass filter is the receiver to
which you connect it.
So there are two questions.
1. What is the "frequency?" This term usually refers to a sinusoid, in
which case the answer is trivial. Presumably the "frequency" meant here
is the fundamental component of the "square" wave, but the true answer
depends on the shape of the on/off switching, which presumably depends
on the "frequency" one has dialed into the device. Is one getting more
or less a 1/N dependence on amplitude at all frequencies?
2. When one refers to the calibrated "levels" of output, is one
referring to the level of the square wave or of its fundamental
sinusoidal component? Clearly, these are related...but which is meant?
What about the high frequency end of the operating range, where the
spectrum may well depart substantially from 1/N (because the trapezoid's
edges are less "sharp").
Neither of these questions has anything to do with the "phase noise"
specification.
John Ragle -- W1ZI
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