VHF-UHF Diplexer

Diplexer is a special filter circuit that seperates 2 different bands. It is different from Duplexer which seperates 2 frequencies on the same band.

There are mainly 4 types of filters: Low-Pass(LPF), High-Pass(HPF), Band-Pass(BPF), Band-Notch(BNF).
Low Pass Filters, apply min. attenuation below designed frequency and max. attenuation above this frequency.
High Pass filters are just the opposites of low pass filters.
Band Pass Filters are only passes signals between designed low side frequency and high side frequency and attenuates all other frequencies.
Band Notch Filters are only attenuates signals between low side frequency and high side frequency and passes all other frequenies.
For BP and BN filters, the difference between low side freq. and high side freq. called as Bandwidth.

Diplexer includes one LPF and one HPF. On the VHF side there is a LPF, which passes VHF singals and stops UHF signals.
On UHF side there is a HPF, which passes UHF signals and stops VHF signals.

There are different type of circuits for filters such as, LC, RC, RLC, active(ie.opamp), digital etc., but in diplexer we are only using LC circuits.
You can access the original page of project from here: www.hamradio.selfip.com/i6ibe/duplexer/duplexer.htm

Note: Use large pcb or box. If you try to build it on a small pcb or box, it is impossible to set large inductors so frequency.
This is why i throw the pcb version into the trash bin and built it into a box.
Two holes at the corners of the box is drilled unintentionally. They don't have any function.