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.
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 only way to make it lie is to not
calibrate it or set a control properly. If using a Tek or other
quality scope, your viewing something pretty accurate. I still think
a scope is one of the better ways of measuring output power while
monitoring the signal for over-modulation and cleanliness. This
method has been used for years.
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.
...
R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org
