Your single antenna cut for 40Mhz - 50Mhz will work through to the UHF bands in theory - but not been anywhere near the right length there is going to be significant loss in the signal strength, so much so that I'd say it's going to be pointless unless the UHF transmission is really strong.
I'd go for 2 antennas - not with a splitter, but with an antenna switch that can be interfaced through TTL/serial or in some similar manner to the scanner, so that the correct antenna is switched in/out of circuit as the scanner runs through it's scan program.
If you can get hold of an antenna switch from a Watkins Johnson 8617 receiver (it will have come out of an 8617 receiver with the HE option installed - see attached picture below) off eBay or off one of the WJ online groups, and let me know where I can find a copy of the BC355N schematic online, I'll be happy to show you how to hack this switch to work with your scanner so that it switches from one antenna to the other as the scanner moves through low VHF across to UHF.
For others who may be interested, this antenna switch is an excellent little box of tricks which can be hacked to work with just about any scanner/receiver.
It switches from one connector to the other around 0.5Ghz (though that point can be moved) - it's good from around 2Mhz - through to over 1Ghz, isolation is good, switches as fast as any scanner is going to jump from one band to another, losses are insignificant and introduced noise is a non-issue. Its versatile (can be hacked to work with just about any hobby type off the shelf scanner/receiver) and will tolerate been located externly so long as it's sealed into a tupper-ware container or something similar. Only downside - needs a small power supply and output coax connectors are not N-types, so will need to have adaptors fitted if you are going to run a long length of coax.
PS - there are loads of other antenna switches around - I only suggest this one because I have used it with literally dozens of different types of scanner/receiver setups in the past in which the switch over has had to take place across HF or low-VHF to the UHF band.
Last edited by benbenrf; 01-15-2013 at 4:18 AM..