View Single Post
Old 7th Sep 2019, 1:09 pm   #71
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Telequipment D75 scope.

In my opinion the various calibration protocols you see for many scopes are those created around a paucity of calibrated lab equipment. Then it leads to many layers of confusion about how to calibrate a scope's vertical amplifiers and attenuators and "custom test fixtures" which assume some special properties but I think are only specific to a few scopes.

The reality is this;

To calibrate any analogue scope perfectly, from any bandwidth up to 100MHZ, three calibrated instruments are required:

The PG506 amplitude and fast rise pulse generator.
The TG501 time marker generator.
The SG503 levelled sine wave generator.

Fortunately, the SG503 is only required for a final bandwidth test, you can just get away without it at a pinch.

The TG501, could be replaced with other frequency references, but the TG501 is hard to beat to set up a scope's time base correctly as its pulses suit the CRT's graticule well and it steps in frequencies like a scope's timebase.

The PG506 is the essential tool. It produces perfectly rectangular fast rise output pulses (Heaviside function on the leading edge) over a range of frequencies with a controlled amplitude. You cannot cobble this together in a workshop or use any other general purpose signal generators, the amplitude affects the quality of the output wave, but in the PG506 it does not.

The PG506 is all that is required for correctly setting up the DC gain and the multiple compensation adjustments and attenuator in ANY scope's vertical amplifier...across all of the attenuator settings without resulting in a corrupted calibration.

The PG506 gives you control of the amplitude and frequency of the test signal while maintaining a perfectly rectangular form. The various square wave frequencies are required to ensure a flat response across the scopes bandwidth, one test frequency is not nearly enough.

In the process of setting up any oscilloscopes vertical amplifier, there is no escaping the fact that this is the type of controlled & calibrated signal required, able to maintain its perfect rectangular form over a huge range of output levels and frequencies. There are other equivalent scope calibrators to the PG506 out there, but the reality is Tek really aced the design with this one and every scope in the world can be better off for it.

When the job is done you can then check the bandwidth with the levelled sine wave generator and make an assessment of the bandwidth, but it will be very close to correct if the adjustments are optimized with the PG506. The levelled sinewave generator is a useless tool for the actual calibration of the vertical amplifiers themselves, because the observer will not notice the effects of any adjustments at multiple other frequency points than the one they are observing.

(For scopes over 100MHz bandwidth its useful to have the TD pulser, and the SG504 generator that goes to 1GHz, I use these additional items to calibrate my 400MHz bandwidth 2465B scopes)

Last edited by Argus25; 7th Sep 2019 at 1:23 pm.
Argus25 is offline