dual

Is it possible to monitor a VHF system (single frequency) and a 700MHz trunked system on the same "channel" position ?

setup= mirror mounted dual firestiks with tunable tip, mounted just over 7'6" apart, 18ft cophased coax. SWR is lower when it is cloudy and colder outside, the brighter the sun the higher the SWR. Am I missing something obvious here, or am I thinking way too much into this? out of curiosity...