On Wednesday 07 February 2007 13:56, you wrote:
Kuba Ober wrote:
Kuba wrote:
Well, if all you care about is *basically working*, then I agree. But
then you don't need a 7603 either. A random 7603 with random plugins will
*basically* work, but most of the time it doesn't really perform as a
dependable 100MHz instrument. Maybe it's my luck, but 90% of the plugins
that I bought in lots on eBay showed signs of being seriously
miscalibrated, and two of my mainframes (7603 and a 7633) were quite
miscalibrated as well; their pulse response was completely off limits and
you need the standardizer for that.
Cheers, Kuba
Kuba,
The origin of many instruments on eBay are government surplus, or surplus
acquired by someone with no calibration skills. In the first case,
metrology (instrument calibration) technicians in gub ment would screw up
an instrument they are trying to dump (or are instructed to do so) so it
gets tagged "unusable". The other case results from uneducated people
trying to fix something that ain't broke.
True, but given such a miscalibrated state, would you trust the instrument for
anything serious?
I guess for basic RF stage alignment you don't even need a scope, an RF RMS
voltmeter with a phase detector/indicator would probably suffice. I used such
a phase-indicating RF voltmeter back in high school to fix an ailing RC
receiver. It had a single mixer, an IF filter & amp, and it'd directly
demodulate the RF, if I remember things right. Due to vibration or whatnot
the two little coupling transformers had the slugs at all the wrong places,
and there was also a little air-wound coil with a couple turns that somehow
got distorted (maybe someone played with it too much) and needed bringing
back to shape. Being a total RF newb it took me a couple afternoons to figure
it out, but in the end I had it working. I had a scope, but all I cared for
was to get the response peak in the right place, and the voltmeter did just
that, and the scope's probe seemed to load the circuit too much. The
voltmeter had a couple different probes, two non-contact ones, and three
contact ones. I don't remember their specs, though. You needed one probe for
the voltmeter, and optionally another one for phase reference.
For non-RF-alignment work, e.g. audio amplifier design/testing/adjustment, you
will need to look at time-domain response, and for that you better had a
scope that's linear in both X and Y subsystems. How can one just assume that
it's the case with an unknown scope and not much to test it against??
Cheers, Kuba
