The experiment of recording to tape did not meet with success.
Here's the hookup diagram:
ZX-81 RF Output ---> VCR RF Input ---> VCR RF Output ---> TV Set RF Input
Before beginning, I connected a regular TV cable to the VCR RF Input and set the VCR to Video. I confirmed that I could tune in, record, monitor, and playback regular TV channel 3.
I disconnected the TV cable from the VCR RF Input and connected the ZX-81 RF Output. Channel 3 is used by the ZX-81.
When the VCR RF pass through switch is set to TV, the ZX-81signal appears on the TV set, but when it is set to Video, the black image appears instead of the ZX-81 output.
I tried recording this and got a tape with no picture as well.
I still think that was a great suggestion because it was a step closer than the composite output jack, but apparently the ZX-81 signal is not being accepted in the VCR before it gets to tape.
(CSnet wonders if a digital video camera on a tripod in front of the TV set is the only answer!
)