Arrow makes the perfect antenna but I thought I could homebrew one at a much lower price.
The main component that differentiates the Arrow from other dual-band Yagis is the diplexer, not duplexer, as it is incorrectly called by Arrow (and others).
A search online located several suitable but expensive diplexers for the necessary bands - and one inexpensive kit ($13) from a US seller on eBay - Steven AI4NV.
The kit arrived today and took all of 10 minutes to assemble.
There are three SMD capacitors and three coils to wind; two on torroidal cores and one air-core. An aluminum tube is included to assist in winding the air-core inductor.
After winding the coils and soldering all 9 parts to the board, it was time to tune the diplexer.
The instructions that come with the kit mention that a dummy load should be placed on the port not being tested, implying that the port being tested is left open. In reality, a dummy load should be placed on both ports.
The idea is to tune each output for minimum SWR with that output's frequency being injected. This will result in minimal insertion loss and maximum rejection of each band from the opposite port.
It is important to make sure that the dummy loads used are adequate up to 450 MHz.
