How to modulate a marker with a square wave

[Notimetolooz]

I have never heard of this method being used before.
Seems kind of kludgy to me.
The author is suggesting to use a marker generator as a TV channel RF source.
Video is always an AM modulation of the RF in the NTSC system.
However this suggested method does not provide the proper sync signals to the TV. Also any shortcomings of the modulation of the RF generator will also show up in the video amp output. Maybe he happened to find a generator that did a good job at modulation.
I would think that a good video pattern generator, which is intended to be used for this sort of things, would be a much better way to make this test.
Also in 1970 affordable digital electronics was just getting good enough to generate high quality video test signals, so perhaps the author's method made more sense.