T/R Switch/LPF Adapter for Power Amplifier

 T/R switch/LPF adapter bare PC Board for PA, w/four LPF module pcb’s – $12


      Four additional LPF module pcb’s – $4


You see many small power amplifier modules on eBay, amplifier plans and projects on the internet to boost your QRP output that would be nice to try. They usually concentrate on the amplifier itself, and leave out the necessary details that make it easy to use, such automatic t/r switching, the needed output low pass filter that broadband amplifiers require, and an attenuator to keep from overloading the amplifier input.

This (2.70” x 1.68”) through hole board allows you to interface a power amplifier to your low power transceiver. It incorporates an RF sensed T/R switch, optional input attenuator, amplifier control, and a post LPF for the amplifier. The LPF can be board mounted for a single band use or for multiple bands through the use of the included plug-in module pcbs. The T/R switch includes an active low and active high for amplifier initiation if needed, and has full QSK on slower CW speeds and semi-QSK for the medium to fast CW speeds; full QSK on SSB. The T/R relay specified is capable of handling 50 watts RF. The documentation has the component values for the band specific 160m-6m LPF’s. There’s a jumper to disable the amp for barefoot operation and another to manually select the TX enable line for adjusting the amplifier bias with no signal. Antenna connections can be pcb mounted female BNC or SMA.

I’m using it to work with the QRPLabs 10W HF PA on 6m, but could be used with a homebrewed or similar amplifiers on 160m-6m. It’s an easy through hole project with readily available components.

Due to the number of variables possible with this project, it is offered as bare pcb’s for the user to tailor it to their individual needs.


Click here for circuit description and parts list


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