Thanks for the advice everyone.
I did try running the Zinwell ZAT-970A D2A converter box from it's RCA outputs directly to Input Video 1 on my TV, and voilĂ*, no interference at all. It seems that the Toshiba DVD/VCR introduces some noise during its input > output route; so by running directly to the TV (Video 1) and the DVD/VCR to Video 2 on the TV, and the Ouput on the TV back to L1 on the VCR, I can watch clear TV and still record it, and use pass-through for the next 5 months. Of note, even pointed at Mt. Seymour N/E direction, I can easily get KBCB and KVOS to the South with the side lobes of my 20 year old Antennacraft "RS VU-160XR VHF/UHF/FM" antenna- they're about 48 miles away in Bellingham, WA.
I put in a new piece of copper RG6 from the Converter box to TV, for analogue pass-through, replacing the push-on patch one used from the VCR to TV, which wasn't copper, or very thick. I should run new RG6 from the antenna to the grounding block, because it is old, but it does look to be in good shape.
And again, thanks for the friendly advice and good suggestions.
