Two options, but not what you are hoping for... You can combine one UHF antenna with one VHF antenna.
1) A passive combiner with a UHF port and a VHF port known as a
UVSJ Taking this a step further, you can use a
HLSJ to combine a low-band VHF antenna with a high-band VHF antenna.
2) An active combiner. Example:
Dual Input Preamp
There are a variety of choices other than the examples I've offered.
A typical 2-way splitter will not provide the isolation and filtering needed to keep the two antennas from interfering with each other.
Four options to do what you are asking for:
(1) a rotator (not really what you are asking for, but functional to a degree)
(2) Conversion to MPEG-2 over IP over Ethernet -
Thread 820 ($) to ($$)
(3) A complex combination of CATV commercial grade equipment ($$$$$).
Custom Antenna Combiner or
Single Channel Digital Signal Processor
(4) John's suggestion below.