(31-03-2013, 11:39 AM)AlanBeckett Wrote: Al,
That's what Advance says it does - see attached for the 'C'.
Alan
Hmm, so I see.
That 'specification' is not exactly 'informative' is it?
Quote: "Freq. range: 15 Hz to 4.5 MHz".
O.K., what's their definition of 'frequency range'? Are those the bandwidth limits for - 3dB? - 1dB ? Without a relative signal level, those 'bandwidth' freqs. are meaningless.
Then we have the 'accuracy' figures beneath: which I can't 'square' with those bandwidth figures.
Quote: "Amplifier freq. response 12 Hz - 200 kHz (100 kΩ / 40 pF load). Response rises to 3 MHz and falls away above that freq."
That clearly contradicts the "15 Hz to 4.5 MHz" figure. So I reckon that we can safely assume that for the purposes of measurement, the bandwidth is actually 12 Hz - 200 kHz. Since the 'amplifier' drives the front panel meter, that would make sense. And when they say "rises to 3 MHz and then falls away", that is so vague as to be a worthless comment!
If this was mine, I'd run my own series of measurements on this, using suitable test equipment: calibrated sig. gen. + calibrated 'scope. As I have said countless times before, equipment whose calibration or spec. you cannot trust is worse than not having that kit in the first place. Without kit, you can sometimes make an informed guess; with kit of dubious spec. / calibration, all you get are measurements that you think you can trust - and then later on you wonder why things are failing to make sense.
Now please don't misunderstand me: I'm not knocking this piece of T & M kit. I am sure that the VM77 series of VTVMs are perfectly adequate for, and are quite capable of, doing their designed job - but one has to know, reliably and with a reasonable degree of accuracy, their limitations - as with any piece of T & M kit, produced by anyone.
Al. / March 31 //
