Category Archives: Low Pass Filters

LOW PASS FILTER BLOCK 3.5-30MHz

This board consist of the following modules:

5 sub PCB with low pass filters chebyshev type for all HF bands. There is place where to be nested one optional LPF subboard (for 160m)

High voltage (210V) scheme (voltage tripler)

Antenna RX/TX switching

SWR directional coupler and measurement of Vfwd/Vref

Optional LPF (160m) connector

This module ensures clear harmonic output of the linear amplifier, also fits the components for antenna RX/TX switching. Following the “click-less” concept, there are no mechanical relays in the circuit. After long searching for suitable power switching component I found VISHAY high voltage rectifier diode S07J (S07M) that met all the requirements for reverse voltage capacity, reverse recovery time, forward current and reverse voltage. So S07J were used in the project to ensure good switching of TX power to the antenna via proper LPF and also reliable isolation between each other low pass filters not selected for this band portion.

High voltage generated from input signal polarizes unused switching diodes in reverse direction ceasing the chance for signal leak. Same votage is used in RX/TX switch for completely disconnecting receiver front end on transmit.

PCB layout
Component side (bottom) values:

Component side (bottom) reference names

Top – connector side:

Picture of the ready board with filter subboards on it:

 

 

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