I've designed an pulsed RF generator (50-100 MHz) and am using a directional coupler to measure power into a 50 ohm dummy load. The forward power from the coupler is plugged into a o-scope (hi Z input). The issue is that I calculate what seems to be too much power (more than expected) that, while possible, I doubt.
My calculation is as follows: on scope I see 100 mV RMS, so this calculates as (0.1 V)(0.1 V)/(50 ohms) = 0.2 mW. Since the coupler constant is 60 dB, this means the mainline power is (0.2)(1e6) = 200 W. This seems high as the cw power during design was 100 W, although the 10% duty cycle certainly could enable 200 W during the pulses. Does this seem correct?
Also of note: the coupler (an older Werlatone, no longer manufactured) is rated for 5 kW. Could my measurements be caused by not reaching some threshold (using too little of coupler's range)? Also I checked the forward-power port resistance using a DVM and got 19 ohms, which I cannot make any sense of- expected short, open, or 50 ohms for this DC measurement. Any thoughts/comments appreciated!