Typo: ¡°SG503¡± should be SG504. The former does the sensing inside the instrument and obligates you to buy an expensive cable to keep leveling quality all the way to the end of the cable. The SG504 puts the sensor at the point of delivery.
Sent from my iThing, so please forgive typos and brevity.
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On Jan 31, 2021, at 2:37 PM, Tom Lee <tomlee@...> wrote:
?Jean-Paul,
He has said explicitly that he used an HP8657B generator. It is a leveled instrument.
He made measurements on several scopes. Those measurements made sense.
I think it is safe to assume that he made the measurements correctly. Whatever errors he might have as a result of cable type, etc. must be small. And in any case, they were small enough to measure a 600MHz bandwidth. It is hard to contrive a scenario where he has an error that shows up only at 275MHz for that one scope, while all others look good.
Help to solve his bandwidth deficit should focus on the scope that uniquely fell short of specification, not on fixturing details, nor on the type of generator used. The leveling loop in that HP sig gen is as good as it gets for a generator that controls level at its output port. The only difference between it and the 503 is that the latter senses level at point of delivery, so the cabling matters less. Again, he¡¯s already successfully measured a 600MHz bandwidth for another scope using the same setup, so the probability that he has a leveling problem is small enough to look elsewhere.
Tom
Sent from my iThing, so please forgive typos and brevity.
On Jan 31, 2021, at 2:23 PM, Jean-Paul <jonpaul@...> wrote:
?Rebonjour, further musings.....
1/ We use a leveled sine cal generator, eg Tek SG503,SG504 etc or HP 8640B to check BW.
2/ less is more... Eliminate cables if possible, the excellent Leo Bodnar 40 ps pulser has a BNC female to connect directly to a 50ohm scope input.
3/ For 1 M ohm input scopes, Feedthru terms are not perfect, we have some old ones or Chinese clone junk that are NOT good above 100 MHz, we recommend the Tektronix BNC 50 ohm feedthru, or the Mini-Circuits
4/ Tweaking transient response is an art not a science, use care, patience and compromise.
5/ like any amplifier, a scope vertical amp can have non-linearity. The response ( transients or BW) may change depending upon the trace positon on the screen.
Enjoy, and happy tweaking!
Amenities et cordialement,
Jon
