In response to Ken's question:
> ... Perhaps there is
> some ITU defined standard for measuring CW keying envelope rise time.
>
The ITU Recommendation ITU-R SM.328 does address this. This is a 74-page
document, called 'Spectra and Bandwidth of Emissions".
It includes:
"#1.20 BUILD-UP TIME OF A TELEGRAPH SIGNAL:
The time during which the telegraph current passes from one-tenth to
nine-tenths (or vice versa) of the value reached in the steady state; for
asymmetric signals, the build-up times at the beginning and end of a signal
can be different."
This document also gives (#1.3 of Annex 1) an approximate expression for
the
"Occupied Bandwidth" in terms of the build-up time of the shortest pulse of
a telegraph
signal (i.e. of emission class A1A) .
In #1.5 of Annex 1 it concludes:
"... As a first approximation, it may be assumed that an out-of-band
spectrum
close to the limiting curve ...[this is a total of 0.5% out-of-band power
above and
below the necessary bandwidth] ... corresponds to a build-up-time
of about 20% of the initial duration of the telegraph dot, i.e. about
1/5.B."
[I.e. 20% of the shortest dot length.]
Just for info. I happened to have this ITU Recommendation on my desk.
73
Darrel, aa7fv.
======================================================
>Ken Brown ken.d.brown at verizon.net
>Sat Nov 19 00:06:01 EST 2005
>
>
>Hi Bob,
>
>Thanks for making the measurements and posting your results.
>
>I would like to know what really is the right way to measure rise time
>of a CW keying envelope. I cannot see how measuring from 0% to 100%
>power output can ever give an accurate and repeatable measurement,
>because the noise level in your instrumentation would have to be
>absolutely zero in order to discern exactly when the power output has
>gone above zero. The same is true of determining exactly when the power
>has reached 100%.
>
>Also I believe that the highest slew rate is what determines the
>bandwidth that the signal will occupy. The steepest slope of the
>amplitude increase should occur somewhere near the middle as the power
>level is rising through the 50% area. In the zero to 10% and 90% to 100%
>areas the slope is not as steep, and averaging those portions into the
>measurement may give a measurement which if used to calculate the
>occupied bandwidth, would result in a lower bandwidth than what the
>signal actually occupies.
>
>Sure, I'm being picky. Inquiring minds want to know. Perhaps there is
>some ITU defined standard for measuring CW keying envelope rise time.
>Maybe someone will tell us.
>
>DE N6KB
>
>
>>I was interested in total rise time, so I measured from 0% to 100%, plus
or
>>minus 0.1 ms as best I could judge by eye, but the very distinct and
uniform
>>waveform made it pretty easy to do at 2.5 ms per division. Quick and
dirty,
>>just to get a rough idea of the relationship between indicated and
actual.
>>
>>
>>
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