From my book, "Live TV From the Moon" (pp129 - 131):
Despite the efforts of Westinghouse, their idea for a converter was ultimately never used during any Apollo mission. A scan converter built by RCA was the unit chosen to convert the slow scan TV signal from Apollo 7, Apollo 8, Apollo 9 and the Apollo 11 moonwalk. Their unit very similar to that devised by Westinghouse, used a stock standard video camera which
had seen use in film-to-video telecine, and in the days prior to videotape was also used to record video onto film (a process known as kinescope). It was a black-and white Vidicon tube camera pointed at a 10” high resolution cathode ray monitor. The monitor had a persistent phosphor which caused the image to remain on the screen for longer than normal. The TK-22 was gated to record 1 frame as it was written onto the high resolution screen.
The output from the camera was a standard interlaced NTSC video signal. 1 full frame of video information was composed from two fields of 262.5 lines which the camera could not properly record from the 10 frame-per-second rate. The first field was recorded correctly, but the second field would be recording off the monitor when the next frame of video information was already being written, resulting in a messy signal which generated a lot of problems in the conversion process.
This snag was overcome by recording the first field onto a video disc recorder which would then repeat the redundant field with a delay built into every second field to allow it to mimic the missing field that the camera was unable to capture. Essentially, the TK-22 recorded the first field, with the disc recorder repeating the fields while adjusting them so that they correctly formed a full NTSC image. This process was repeated to form the “missing” 3 frames of NTSC video and the resulting output was a fully compatible NTSC video signal. There was one major drawback, which unfortunately the technology of the time could not solve. The picture was unavoidably degraded as it was optically converted and this on top of the already reduced resolution of the incoming slow scan TV signal.
The system controls were rather straightforward. A test pattern generator was incorporated into the converter to assist in calibration prior to receiving an incoming signal. The type of slow scan signal could also be selected between the 10 and .625 frames-per-second rates, though in the case of Apollo 11, the high resolution mode, while always available,
was never actually used. A variety of controls relating to video synchronization and video level settings were accessible to adjust the signal, in most cases the controls were separately configured for either the standard or high resolution modes. The final output path allowed image enhancement and adjustment of the video disk recorder. The resultant signal could be made as visually appealing as possible, although despite all the controls, the fact was that the slow scan image was optically converted-and that resulted in a loss of resolution of the picture.