Of course you're right. It really should be measured like a pulse or square
wave, in the standard way. After all it's between 10% and 90% where most of
the "action" is anyway since this is a sinusoid shape. So the earlier data
is too high by a little over 20%.
Sorry about that, guess it's the inevitable rot setting in after spending
the last 10 years mostly on the software (dark) side.
Rather than fudging the figures with a guesstimated correction factor I
thought it safer to make new measurements the right way, of elapsed time
between 10% and 90% max amplitude.
Results in ms, average of 5 measurements:
Indicated Measured
3 1.8
4 2.2
5 2.8
6 3.4
7 3.9
8 4.4
9 4.9
10 5.5
About as expected. Likely no better than +/- 0.2 ms, but enough to give me a
rough idea. To hit my rise/fall time target of 5.0 ms I've set the rig to 9
and will go on with life.
The advice from N1EU to just set it 8 is perfectly sound also, but if I
can't trust the user interface indications then I want measurement data so I
can vary the parameter as I wish with confidence. I hate to appear
pig-headed, but after all it's I who am responsible for the bandwidth of my
signal.
It's probably the signal spectrum that is even more important to know, wish
I had a sufficently high resolution spec-an at hand to look at sidebands
within a few kHz of the signal.
Anyway, I'm glad the gentleman passed along the warning to those like myself
who weren't in the know. Maybe Santa will bring me a monitor scope!
Bob NW8L
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Ken Brown
Sent: Friday, November 18, 2005 10:41 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] cw settings
Where do you measure the rise time? When I was in the oldsillyscope
calibration business, we measured rise time of the leading edge of a square
wave as the time between 10% amplitude and 90% amplitude of the waveform.
That makes for a lot less intrepretation of where the rise begins and where
it ends, which you would have to do if you measured 0% to 100%.
I'm not sure about the latest Tek scopes, but the ones I calibrated have
dashed lines to indicate those points. with the square wave set to cover six
vertical graticule divisions, we measured the rise time from the lower
dashed line (1/2 division up from -3) to the upper dashed line
(1/2 division below +3). This came right out of the Tektronix calibration
procedure manual in the section for checking whether the scope's vertical
rise time met spec. (Yes I know that 0.5 does not exactly equal 10% of 6,
but it is close enough)
DE N6KB
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