Also understand that the FrontEnds of these Cheap Chinese HTs are NOT very selective, and very subject to Overloading from local Transmitters.... which is an inherent Issue with Repeater Operations.... Crossband would be a LOT easier to accomplish. A good Mobile UHF 6 Cavity Duplexer can make a UHF 5Mhz Split Repeater, not to hard to accomplish, especially at the 5-8 Watt Tx Level.... Lots of Portable Repeaters have been built using these type of Duplexers, and made in Pelican Cases, for Emergency Deployments.... One question you will need to get worked out is finding the COS Signal, (Carrier Operated Squelch) in the Receiver HT, and bringing it out to be used to trigger the PTT of the Transmitting HT... I don't think that the COS Line is available in these HTs, externally... Using the VOX function will be problematic, as it may also trigger on local Noise, coming in from the local Mic... COS is a much better, and more Positive Control....