Four bandpass filters are used in the RX and TX path to cover all HF bands. Filters are implemented using standard values capacitors and inductors.
This is one of the most simple, compact and easy to build filters, not inferior to the filters of other designs.
Recommends for novice or ham radio who do not want to make windings.
Filter switching is achieved via CMOS switches SN74CBT3253, two of them – one at the input and one at the output to prevent crosstalk. Two parallel data lines are used for control, plus the RX/TX lines that selects Receive or Transmit mode. Truth table is included in the schematics. Input DC of bandpass filter is 8-15Volts, but the Recommended input voltage for IC control is 3-5Volts.
It is very convenient to use DDS synthesizer for switching bands, however switching could be easily realized by standard rotate switcher.
Connectors on board
- DC – power supply of filter is 8-15V
· RX ANT – RX input signal from antenna
· RX OUT – output from bandpass of rx path -> going to mainboard of receiver/transceiver
· TX IN – input from motherboard of transceiver or transmitter.
- TX ANT – output from bandpass -> usually going to power amplifier or antenna
This design has standard values of inductors and capacitors and If elements soldered accurately and correctly it works from first power on and no need the adjustment.