11801 calibrator rise time

Reginald Beardsley
 

I think I figured out why the calibrator rise time measurement doesn't read to spec. I warmed up the 11810 for about 40 minutes to do the Enhanced Accuracy adjustments. That seemed to go fine except afterwards when I measured the rise time I was getting >400 ps. The 11801 will remember the incorrect settings through a power cycle.

If you do the Loop Gain adjustment in the Enhanced Accuracy menu it resets something which results in incorrect values. If you go to the Utility menu and press Initialize you should now be able to set the Trigger to Internal, press Autoset, adjust the time base, turn on Hardware measurement and get <35 ps rise time.

Unfortunately, it does not appear to be possible to measure the rise time on more than one one channel.

I think a bunch of the Chinese DSO designers must have spent a lot of time using an 11801 and thought that was what a scope UI should look like. Even after reading all the way through the User manual the UI is still confusing because of the strange locations of various settings.

The tip off came from this line on p 82 of the User manual:

"Whenever you begin a new task using the 11801. you should initialize the system so that all the settings are at "factory default" . That way you do not get unexpected results because of settings remaining from the last use of the 11801."

BTW I have a 2 port divider feeding the upper channel of my SD-22s and the waveforms look to be exactly the same. The pieces of hardline from the divider to the heads are different lengths and I have not been able to shift one relative to the other to see how closely they overlay as there is a 340 ps delay between the two. The divider increases the rise time to 42 ps. It's an MBC Technology unit. No frequency rating specified.

I just discovered that it reset the time base readings when I removed the splitter and turned off one channel to take a look at how much of the 7% overshoot was the splitter which it turns out is about 5% of the total.

There's a little bit of ringing on the calibrator step at 12.2 GHz which is probably the result of reflections where the semi-rigid SMA cable connects to the 3.5 mm calibrator and sampling head connectors.

I am quite agog at how precise this thing is. Getting the full performance out of it will take some serious skill.

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