Tektronix 11801c trigger - Page 1
Forum section: electronics / projects

author: cncjerry
author_rank: Unknown
timestamp: December 10, 2022, 08:52:13 am
content: The 11801 is like the csa800 and other communication systems analyzers. They dont have a typical trigger timebase. I have 2.5Mhz and 1hz signals and I would like to view the phase difference between them. I tried running the 1hz signal into the trigger input and it doesnt seem to work, or if it does, it must take a very long time to sample the signals as I never got a trace. By the way, I have a pair of sd26 sampling heads in it. I then triedinput to trigger using the 2.5Mhz thru a splitter with one split going to the channel and the other to the trigger . That gives me a view of the 2.5mhs signal but of course the 1hz is outside the capture window.So I'm wondering if anyone with experience with this or other CSAs can figure out a way to measure the phase between 2.5Mhz and 1hz with this beast? I have other scopes but his thing has very low jitter and very accurate when you get it setup. The other thought was to possibly use the delayed sweep but how would I know what 10Mhz pulse it was triggered on unless I somehow gated them both when the 1hz started?Thanks,Jerry

author: KrudyZ
author_rank: Frequent Contributor
timestamp: December 10, 2022, 06:27:44 pm
content: Using the 1 Hz signal as the trigger will indeed take a long time as it will only be acquiring one sample per second.The scope generates a random sample delay from the trigger to sample what it sees on its sample head inputs. I think it won't update the screen until every slot has been filled, but I'm not sure about this.There is a minimum delay of 25 ns from the trigger to when it samples, so you would not be able to see the edge of the 1 Hz signal if you were to simply split it into both the trigger and a sample head input. Of course, you would need a proper 50 Ohm splitter, not just a Tee.Tektronix sold delay lines for this purpose that included both the splitter and the delay required to see the trigger event with a scope channel.https://w140.com/tekwiki/wiki/DL-11The 11802 model had the delay lines built in.You need to make sure that your trigger settings are set properly. It's a bit finicky. I would suggest you start with a faster trigger signal from a function generator to make sure your setup is OK.In addition, you will run into the problem that a 2.5 MHz signal is still very slow (400 ns period) and unless the 1Hz edges are expected to be very close to the 2.5 MHz edges you would have to use fairly slow horizontal timing settings since the maximum samples of this scope in a trace is around 5000. This would kind of defeat the whole purpose of using this type of instrument.I would suggest to just try to measure the jitter as the trigger to 2.5 MHz delay, rather than trying to catch both 1 Hz and 2.5 MHz edges in the acquisition.You first zoom out to capture >400 ns and then adjust the delay and the time base to zoom in on the edge transition.It might feel a bit sketch as what you are measuring is the sum of the signal jitter, trigger jitter and delay jitter. However the latter two are specified in the 11801C data sheet, but I'm not sure if this was guaranteed down to a 1 Hz trigger rate.

author: cncjerry
author_rank: Unknown
timestamp: December 11, 2022, 05:01:54 am
content: Thanks for the reply, Krudyz.last night, actually around 2am, I drug this beast out again and tried the higher trigger rate first and even at 10khz, the signal was already drifting around so I couldn't find it.I thought for sure I was able to do this once, that is, look at the leading edge of a slow pulse while another was in an alternate channel.I'm testing a tdc7200 TOF chip and I wanted to see where the start/stop delta got too small. I tried with my Siglent scope as I didn't want to drag any of my others to this test area and it shows nice stats but I don't know if I trust them. There are other ways to do this and I have several thousand pounds of T&E but I had this scope sitting here and wanted to give it a shot.If I knew how it would trigger vs the 1hz signal, I could cut a delay line to length.I