I recently purchased the RD JDS6600 40MHz signal generator from a US vendor on ebay, and received it last week. For the most part I was pleased with the unit, until I discovered this anomaly. When you generate a pulse output with a duty cycle other than 50%, you end up with 5ns of jitter on the pulse.
I am including some scope shots that show this behavior. I have the generator configured to generate a 1VPP pulse, it is connected to my scope (with 50
termination enabled) using a RG-58 cable.
The first image is a 10MHz pulse with 50% duty cycle, this looks fine. The second image is the same frequency but a 40% duty cycle, you can see the 5ns jitter. The next 2 images are taken at 20% duty cycle at 10MHz.
I then tried a few other frequencies, I've included a picture of a 1MHz 40% duty cycle and 500KHz at 60% duty cycle....the 5ns jitter remains. It really doesn't matter what frequency, anything with a duty cycle other than 50% has this problem. To make sure I wasn't having some sort of triggering problem with my scope, I dug out my boat anchor HP 8116A function generator, and a 10MHz 40% pulse looks as it should (show in the last picture). So this is odd behavior unique to the JDS6600 unit.
I am assuming that the 5ns jitter comes from the 200MHz sample rate that the unit has. I don't really know how DDS signal generators work, but I am assuming this 5ns is an artifact of the 200MHz base clock. Is my assumption correct?
To investigate a bit futher a took a look at a 10MHz 40% duty cycle pulse on a HP33120A generator, and it looks fine with no jitter.
So what's up with this? Has anyone else observed this? Does a Feeltech FY6600 have this same issue? If not I might send this thing back.
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