--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Oct 24, 2006, at 9:05 PM, craxd wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Oct 22, 2006, at 5:20 PM, craxd wrote:
Jim,
It's a wonder Tom didn't add a "by the way" saying, scopes and
dip
meters are very inaccurate and should never be used. : ) At
least
he
answered you by e-mail, he never would me.
He did not tell me this via e-mail. He said dipmeters were
worthless
during a discussion of various means of grounding grids after a
dipmeter measurement showed a result that contradicted his dicta
about grounding grids.
No, I meant I wouldn't doubt that he would have said
this to Jim.
If a scope is calibrated properly, or a dip meter the same, they
can't lie. They can only show you the truth.
That IS the problem here.
If a dip meter shows a
resonance, there is a resonance at its tuned frequency. Forget
reading the freq off the dial, simply couple it to a known
accurate
freq counter, it will show the truth if you want precision. A
calibrated scope can only show a waveform that it produces from
what
it sees at the input jack.
Correct. He didn't like the fact that an oscilloscope indicated
a
worst-case potential in a SB-220 that was only about 1/3 of what
he
predicted it would be. This potential is on the verge of arcing
the
Tune-C, so even if the voltage tried to rise much higher, the cap
would zap and limit the voltage like a zener diode. The reason he
wanted the potential to be higher was to explain away what I said
was
parasitic arcing by the SB-220's occasional 110MHz oscillation.
The peak or peak to peak voltage one reads is exact,...
Porcine shampoo. I'm a guy who used to calibrate oscilloscopes.
Wouldn't you agree they're exact to within their tolerance?
If the cal equipment used is correct, and the scope is ran
in a similar enviroment temperature wise, etc, it should show
close to the same as what it was calibrated to read. That is
provided it's withing calibration and hasn't been tampered
with. I'm not saying it's exact with no deviation, but it's
one of the most exact ways we have reading an AC voltage. 3%
or less tolerance is pretty darn good. According to the
Tektronix manuals, they should be capable of better than 3%.
A calibrated oscilloscope is one way power meters can be
calibrated
and it's much faster than using a bomb-calorimeter. However, an
oscilloscope is as useless as tits on a boar hog for measuring
cleanliness of a SSB signal.
Well it's according to what you term clean. Harmonics no, unless
you
build or use a front end for this like the poor mans spectrum
analyzer, or one of the commercial add-on units. Over modulation,
hum, noise, regeneration, and parasitics can all be seen using a
standard scope.
But not SSB IMD.
...
R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org
Best,
Will
