(05-04-2011, 08:56 PM)Skywave Wrote: Thanks Rob.
50 Hz → 20 msec.; 25 Hz → 40 ms. Somehow I get the feeling that those times are far too short for a sweep time; somehow I get the feeling that something in the region of 0.25 sec. → 2 seconds is appropriate.
[edited - by Al.]
Al.
Must have been having an 'off-day' when I wrote that: what a load of nonsense!
Common sense tells us that on the one hand you need a sweep rate that is above a certain low value to avoid flicker on the screen. If it is really too low. e.g. 1 to 2 seconds, the phosphor on the CRT screen will not have a long enough persistence time for the image to remain visible. (Assuming a 'scope tube with an 'ordinary' phosphor).
On the other hand, the sweep rate must be below a certain high value that will distort the resulting response, simply because the rate of change of the input frequency is faster than the rate that the item under test can respond to. (This is obviously related to the Q of the tuned circuits and the degree of the mutual coupling between windings).
Consequently, there is quite a wide range of suitable times, the exact timing somewhat dependant on the response time of the item under test: Gary's range of 8 → 14 msec. is quite sensible & suitable (most applications).
Right then - having subjected myself to a self-administered public reprimand
, further investigations have revealed that I was being led up the electronic garden path and consequently became confused. I had carried out the initial experiments using an IFT can from the 'junk box'. It proudly stated '465 kc.' on its case; it was lying! :@ Subsequent elementary measurements established that it was, in actual point of fact, a 1.6 MHz IFT !Hence, when I set the sig. gen to sweep @ 465 kHz ± 50 kHz: no 'humps' !
And with that, the rest of this tale is obvious . . . but the experiments continue; perseverence will prevail . . . watch this space . . .
Al.
