Last year I bought a dual band Arrow antenna with the intent of hitting the local repeater with my HT, but also leaving open the possibility of using it on SOTA activations and for satellite work. Since then our club has switched repeaters to a more central 2m location, so I looked into how I could get on the air with other hams on VHF throughout the country via satellite. Though Arrow sells duplexers for a modest $60, I intended to make a project out of this and investigate how I could over engineer a solution to this problem myself.
Although I am confident in my ability to synthesize two 5th order passive filters for frequencies <500 MHz, it is much quicker to use some google-fu and find values for the capacitors and inductors needed to create a passband in the 2 meter and 70 cm ham bands. I used 0603 and 0402 components to minimize the space and insertion loss that would be seen for each branch of the duplexer.
After using ADS to layout and simulate the expected performance for my new gadget, I sent my design to Advanced Circuits, a quick turn PCB fab located just outside of Denver. Being the first time I’ve sent out a PCB for my own personal use, I found the process to be easy enough, though if you aren’t familiar with PCB manufacturing processes, it may be difficult to navigate their online forms without dialing their number and getting some help (the help topics throughout the form left much to be desired). While waiting for my PCBs to arrive I modeled up an enclosure for my duplexer and sent it out to the machine shop at work.
After receiving my PCB and machined aluminum enclosure, I quickly assembled the board and headed to the local hardware store to get the fasteners needed to complete my project.
Overall, I am pleased with how everything turned out. I was able to measure 1.3 dB insertion loss through the 2m path and less than 2 dB of insertion loss in the 70 cm path, though admittedly I performed this measurement using a edge launch connector to measure the performance before the enclosure arrived. The next step will be to get this on the air!