Right tool for high power VSWR Measurements in a Pulse

[qwaarjet]

I have device that generate a 500W 13.5Mhz Pulse for ~1ms and can do that about once every 10s. However I don't believe I'm getting good matching between my RF source and my Load (which is capacitive and cannot be changed) What is the right tool for measuring the VSWR of short pulses in line at these kinds of powers. I haven't found any "probes" that meet all my criteria. The VSWR meters I have can only do average power over several 100mS at best.

[N2IXK]

http://www.birdrf.com/en/Products/Power-Measurement/DPS-Series-Directional-Power-Sensors/5010-Series_Directional-Power-Sensors.aspx

[pa3bca]

http://www.birdrf.com/en/Products/Power-Measurement/DPS-Series-Directional-Power-Sensors/5010-Series_Directional-Power-Sensors.aspx

Less expensive option:
First you need to know what the impedance is that the transmitter "wants" to see.
Then: use a funcgen to generate a 13.5 MHz signal and measure the SWR. using the funcgen as the "transmitter"
If you use a 50 ohm SWR meter it will show you the SWR (for a 50 Ohm system).
Alternatively (and better because it will also give you the phase angle and thus the reactance) measure both current and voltage with a scope (open up your VSWR meter and attach the probes directly to the voltage and current transformers output) or build your own meter using two say 40 turns amidon ferrite cores. In that case you can create an SWR meter for any impedance you like...

(My assumption here: the impedance of the load is not dependent on the power into the load...)

[qwaarjet]

I actually have those Bird power meters but I  would need to send pulses at about 10Hz for them to work and my device can't  run that fast. something like that but with single pulse measurement capability would be Ideal.

[Rory]

A directional coupler and dual channel storage oscilloscope can be used to measure low duty cycle pulse transmissions.
Here's an example of a suitable device for a 50 ohm system.

http://www.ebay.com/itm/DDC-1-Dual-Directional-Coupler-/201111343834?pt=LH_DefaultDomain_0&hash=item2ed32b92da

Data sheet here:
http://preciserf.com/wp-content/uploads/2012/06/datasheet-DDC-1-v3.pdf

As a corollary to pa3bca said, an RF load doesn't require the transmitter to make VSWR measurements. You can use a return loss bridge/directional coupler and a spectrum analyzer with tracking generator, or even a function generator as your signal source to measure the return loss and hence the VSWR.  An RF impedance bridge would also be very useful to get the actual r+jx measurement which would be helpful in designing a matching network. Check out W2AEW's videos on Youtube for a demonstration.