This page dedicated to a low and high power diplexer design and implementation.
I would start with low power diplexer.
The design is a combination of LPF and HPF circuits with LC traps for 40 and 80 meter bands to increase band isolation.
Some numbers I achieved for 200 watt diplexer:
- Insertion Loss (IL) < 0.1dB.
- Band Isolation > -35dB for 40M band
- Band Isolation > -30dB for 3.5-3.8 MHZ (lower isolation above 3.8MHz)
- Return Loss (RL) > 27dB
- 100 watt output power with 100% cycle
- 200 watt output power PEP
Please, see schematics below – a Cauer (Elliptic) type.
Please, see schematics below – a Chebyshev type.
Please, see Diplexer low power graphs below built based on a Cauer type.
- The difference between filter types is not a significant to discuss it but two schematics allows to chose more suitable capacitor’s values.
Below is a High Power Diplexer for 40 and 80 meter rated at 3000 watts of an amplifier output power.
- Band Isolation > -35dB for 7.0-7.3 MHz
- Band Isolation > -30dB for 3.5-3.8 MHZ
- Return Loss (RL) > 30dB
- 1500 watt output power with 100% cycle no cooling required
- 3000 watt output power (50 CFM cooling fan recommended)
- 1411ZU 17″ long Hammond enclosure
The 40M band below:
The 80M band below:
Graph below is an Impedance ([Zs]) and VSWR from Antenna port: