Johnn,
You will lose some signal if you connect two devices to the same antenna.
Martin Lynch has the following item or check web.
The SP – 3 (RF Systems) splitter makes it possible to connect two receivers simultaneously to one wideband- or VHF-UHF output of an indoorunit. Both receivers operate if they are connected to their own antenna.
The high isolation of this splitter assures that both receivers are completely separated: there is no mutual influence such as signal loss or birdies generated from one receiver into the other. The frequency range of the SP – 3 covers 10 MHz – 2500 MHz.
This will stop any interaction between the two receivers and keep loss as low as possible.
There will be some signal loss but thats price you have to pay.
Good quality coax and connectors must be use at all times.
Regards
Paul Mw0cvw EGGP/EGNR