I need to make myself more clear. This is all about a standard composite video signal with no audio sub-carrier. Also this is all about a B&W video signal, meaning no color information.
Maybe is this easier to reproduce now?
Under that subset, then using a pair of PNP fast transistors, emitters tied together, base of one to the logic/RF pulses and the other to the video with sync tips at zero, (probably need "base stopper" resistors)
, collectors to Vcc, will work as a fast and nasty video modulator. This was the old "non additive mixer". . . Use low capacity (Cob < 5 pfd) high ft > 300 mhz devices. (The 2N4917 comes to mind) A simple diode clamp (we liked germanium OMC28's) will keep the sync tips at ground.
The fancy alternative would be a schottkey diode limiter out of the logic instead of the transistor, but that gets into temperature drift issues.
By using a NPN emitter follower after the NAM, it keeps the temperature tracking issues fairly close. It will take some RF linear amplification if you need appreciable power other that a few microwatts.
However, this is not a "logic" solution to an analog modulator, it is the analog use of logic chips like we used to do with 914 Fairchild RTL chips.
---------- Post added at 10:55 ---------- Previous post was at 10:10 ----------
Under that subset, then using a pair of PNP fast transistors, emitters tied together, base of one to the logic/RF pulses and the other to the video with sync tips at zero, (probably need "base stopper" resistors)
, collectors to Vcc, will work as a fast and nasty video modulator. This was the old "non additive mixer". . . Use low capacity (Cob < 5 pfd) high ft > 300 mhz devices. (The 2N4917 comes to mind) A simple diode clamp (we liked germanium OMC28's) will keep the sync tips at ground.
The fancy alternative would be a schottkey diode limiter out of the logic instead of the transistor, but that gets into temperature drift issues.
By using a NPN emitter follower after the NAM, it keeps the temperature tracking issues fairly close. It will take some RF linear amplification if you need appreciable power other that a few microwatts.
However, this is not a "logic" solution to an analog modulator, it is the analog use of logic chips like we used to do with 914 Fairchild RTL chips.
Sometimes I get focused on the wrong rabbit hole.
There are very inexpensive chips (LM1889N historical exemplary) that produce very good quality (5% DP/DG) video at RF with color and audio. Using LSTTL to make video is akin to designing a wheel with flat surfaces. The following doesn't include the vestigal sideband filter required for flat receiver response but the circuit is pretty simple to reproduce:
**broken link removed**
I bought my daughter an entire AC mains powered RF modulator for $5 this past Christmas. . .