Article below is a part of the assembly process of the UHF duplexer – main article is HERE.
Drawing below shows a [AL100] – 28mm Copper Conductor made of copper tube cut to the correct length.
Main purpose of the part: the conductor settles a desired frequency. I was hoping, after setting up correct length for 28mm Copper Conductor RX, that the safest length is 156.4mm which I expected that it will set up the frequency to roughly 440.000MHz.
For some reasons 156.4mm length brought the resonance frequency way higher than I expected. Unfortunately 156.4mm long conductor sets up resonance frequency to about 447.000MHz – but to do not panic – the final tuning can l be done by the copper rod TX at the end plate bottom side! The only one problem is when the conductor resonance frequency is too low – it means you have to chop off a bit from it.
Generally I found that every 1mm changes the resonance frequency of the duplexer cavity roughly by 2.3MHz.
*** I will probably soon exchange the copper TX conductor with the new one, longer 3mm, which will be 159.4mm, to get the resonance closer to 439.7125 MHz.
![](https://www.rozenek.com/wp-content/uploads/2022/11/AL100-28mm-Copper-Conductor-TX.png)
![](https://www.rozenek.com/wp-content/uploads/2022/10/duplexer-conductor-soldered-to-a-copper-plate-scaled.jpg)
Soldering the copper conductor to the plate is achieved by using a special jig. If the plate lies on a metal surface, the heat from a gas plumbing welder will get dispersed. The jig will also help with soldering coupling loops.
![](https://www.rozenek.com/wp-content/uploads/2022/10/duplexer-catity-soldering-jig-heat-isolation-scaled.jpg)
![](https://www.rozenek.com/wp-content/uploads/2022/10/homebrew-duplexer-central-conductor-soldered-to-a-copper-plate-scaled.jpg)
![](https://www.rozenek.com/wp-content/uploads/2022/10/all-soldered-conductors-scaled.jpg)