(20-04-2011, 08:52 PM)Yorkie Wrote: About the only use for a 'scope on radios that I can think of is setting up the IF stage, which requires a signal generator, a frequency counter, and a wobbulator. Most people are content with just using a signal generator.
So why, I wonder, do so many radio hobbyists lust after 200MHz digital storage scopes and the like? Ask them the question and they don't know the answer. (Big boys toys?).
David
When I'm doing almost any type of electronic design or repair work, after the Fluke DMM (and occasionally the AVO 8), my 'scope is the next essential item of test equipment I have and regularly use; it's simply instinctive to switch it on and have a 'poke around' when tacking any fault, other than the "no d.c. rails" symptom. Properly used - and recognising its limitaions - a 'scope can tell you far more what is 'going on' in any electronic circuit that any other single piece of test equipment: the list is simply too large to detail it!
As for "Why are 'scopes that 'go to' 200 MHz so popular", I can only speak for myself. On account of my radio interests, I frequently have the need to get some idea (see further down the page) of what's going on at freqs. in excess of 100 MHz. Now there are several things that need to be recognised (and which are frequently overlooked or are mis-understood) in the "200 MHz 'scope" animal. First, and I assume that this figure relates to the vertical amplifier & not the timebase, is this question: Is that "200 MHz" the response of the vertical amplifier, from BNC input right through to the Y plates, at - 1 dB? Or -3dB? Or worse? This "200 MHz" figure rarely turns out to mean a perfectly flat response to 200 MHz, and rolling off after that. (And what is the rate of that roll-off, too?) And then secondly there is the frequently overlooked characteristic of the probe: your 'flat to 200 MHz 'scope' will not be 'flat' to that freq. at all with most 'probes - unless they are the very expensive 'compensated - at - the 'scope - end' types.
As for digital work, a 'fast 'scope' - and especially if it has a delayed time-base and is a storage one - is essential for looking for fast glitches and other abberations that didn't 'show up' - or were overlooked - at the design stage. And with any type of pulse train, the ability to accurately measure the rise time can be very important: fast rise times require a fast 'scope - typically a "200 MHz" type - or more. Again, relevant to logic circuits.
And finally, when it comes to aligning IF amplifier strips, this is probably the one area when I use a 'scope the least! That is assuming that the amp. is 'behaving itself' and is not doing something horrible like oscillating, has gone very low gain or distorting, for example, (caused by a defective AGC line).
In terms of 'importance to me', my list of test equipment is as follows:
Fluke DMM.
Tek. (or HP) 200 MHz 'scope (+ quality probes).
HP 8640B sig. gen.
'Home brew' LV d.c PSU (adjustable).
Marconi frequency counter; (1 GHz).
Anritsu (or Advantest) spectrum analyser.
Marconi 2202C synthesized sig. gen.
'Home-brew' AF sig. gen. - sine, square, TTL, pulse and ramp outputs.
Wide freq. range comms. receivers: Racal RA-17 and an Icom R-7000 (goes to >1 GHz).
As you can see, the 'scope is well up on my list! I suppose it all depends on what your interests are & where they take you.
Finally, whilst on my 'soap box', I must stress one point that is often not fully appreciated: a piece of test kit that 'tells you lies' is worse than not having that item of test kit in the first place! In the latter case, the worst that you can do is make an inspired guess; in the former, you trust what you are told - and can waste a lot of time as a consequence - or worse! :@
Al.
