A new product is coming to help save your old RF only TV. The Reflex RF is from MisterAddons. This compact piece of hardware allows you to easily convert your NTSC composite video and stereo audio into NTSC RF coaxial. You can send in your AV signal through the RCA inputs, then connect the coaxial end to the input on your RF TV. Power on the TV and tune it to Channel 3 or 4, then tune the Reflex RF to match the channel on the TV. Send in the AV signal and immediately you will have your signal on your RF TV. The Reflex RF is powered via a USB C port.
The picture quality from the Reflex RF was really good on every TV I was able to test. I did not have any issues with interference on the RF signal. The Reflex RF was tested for lag with the Time Sleuth. It performed well adding practically zero lag to the video signal. Unfortunately, the device is not designed for PAL or SECAM support. The Reflex RF is not currently for sale, but MisterAddons does have a listing for the device: https://misteraddons.com/collections/reflex/products/composite-to-rf-adapter.
You can go to that listing and send an email if you are interested in purchasing the Reflex RF. If there is enough interest in the product, a production run will be generated. The price is $40. For more information, please check out the video review.