On a sunny day (Tue, 08 Dec 2009 18:18:50 -0800) it happened John Larkin wrote in :
Many decennia ago, and this also touches on that Tek patent for input isolation that uses a modulated carrier via a transformer, I had a big Philips tube color TV. I also had their first video recorder, a tape recorder with 1/2 inch tape IIRC. As tube TVs in that time has no mains isolation, chassis always live, Philips provided a little box with that recorder, it consisted of a 38 MHz (or there about, basically TV IF) video modulator. The box went into the TV, connected to the IF via a relay IIRC, and provided it with a floating video + audio input. That was one thing, and predated the Tek patent by say, it was from 1968, Tek's applied 2002, makes 34 years YES THIRTY FOUR YEARS. But now the clue, as related to this. To display some waveforms on that big color TV screen (well 61 cm was big in that time), I designed a little circuit, it looks like this: ftp://panteltje.com/pub/TV_scope_img_1679.jpg What is does is create a dot on the TV screen that can be moved in X and Y direction. the 2 window comparators compare the H and V ramp against an X and Y DC voltage. The size of the dot is set by the width of the windows, so a square dot.
When you only use the V comparator, you would get a horizontal line displayed on the TV as set by the Vpos pot. If you put a *signal* on the Vpos pot, you would see the waveform as with a 64 uS timebase... So, if you tested signals that were related to the TV H sync, the display would be rock solid. I used BFY90 transistors to make fast window comparators, and you cloud easily see the spikes on the output of a TTL gate in a 500 kHz signal (is 32 x 15625 Hz). Beautiful, and if course that Philips IF modulator box provided the needed 100% isolation :-)
So, Tek people, here is your prior art, the Philips recorder was the LDL 1000. And here is my prior art to use it as a scope, think I could produce some witnesses who did see it in operation in my place. KIllall patent trolls kill kill kill kill kill kill kill