I'm using a N5171B to generate 50-MHz pulses, about 1us wide and 10us apart, and viewing a pulse on an oscilloscope. I've noticed that for an arbitrary pulse period (say 9 or 11us), the phase jumps around (for one pulse, the leading edge may be positive, and for another pulse, the leading edge may be negative). If I set the period to exactly 10us, then I get a constant phase. Is there a way to keep a constant phase for an arbitrary period? Or, if not, what are my possible choices of period to ensure that the phase is constant? Perhaps multiples of 10MHz?
You only get "constant phase" when the PRI is an integer multiple of the RF frequency.
Example:
RF = 1 GHz, RF Period = 1e-9, A PRI of 100 us will have constant phase because it is exactly 100,000 time the RF period.
If you change the RF frequency to 1.000001 GHz the RF period becomes 0.999999e-9. The PRI is now 100000.1 times the RF period. The phase at the start of each pulse is no longer constant.
Non-constant phase. PRI = 5/4 * RF period.
Constant phase. PRI = 5 * RF Period
Note: You could also get phase jitter on the pulse if the reference of the RF generator and the Pulse generator are not tied together. The signals could wander relative to each other.
Hope this helps.
Pete