Measuring height of Ionosphere with Flex 6500

I have a friend who measures the height of the ionosphere with a transmitter/receiver and O scope by pulsing a signal at 1 microsecond at a repetition rate of 100 pulses per second.

The first pulse on the display is the initial signal. The second pulse displayed is the F1 layer and the next pulse is the F2 layer. The timing between the pulses is the round trip time from which the distance can be calculated.

If it is possible to create a 1 microsecond pulse on the Flex, and receive it in another receiver on a second antenna, the distance could be calculated.

As a "ballpark" figure, 500 miles up and 500 miles back is 1000 miles. At 186,000 MPS or .0000053763 seconds per mile, it takes .00537 seconds for a round trip. About 5.37 milliseconds should be easy to display on a scope.

Here is the challenge: How do I create a one microsecond pulse on my Flex 6500 ? I looked at a CW pulse and at 100 WPM fastest keying speed, the pulse is far too wide, about 10 msec, as I recall.

Could an external keying source key this at one microsecond? Or could SSB be used and employ a one microsecond pulse of audio in the mic input ? Or is there another means to key this ?

Please note, I am not asking for any changes in Flex software or hardware. Thanks for any ideas. Best 73, Jim KD1I