I've had good luck with a Curtis video sender. Mine runs on UHF channel 14. I get a range of 200 feet with it just sitting on the table and can walk anywhere in the yard with a pocket TV and receive the signal.
Looks like this, just with Curtis branding. About the size of a deck of cards.
There's a few models and brands out there, and a few different frequencies. Some running around channel 12 or 13, most seem to be on the low end of the UHF band