Since I’ve got my radio amateur license I’ve reached the limits on the band pass filters integrated in the RSP1A receiver.
My location is near some high power transmitters and they where constantly overloading the receiver’s front-end. That created a lot of false signals and a high noise base line that made HF reception difficult / impossible on some days.
To fix it, I had to create a set of band pass filters that can be attached in front of the receiver. Another requirement was the ability to electronically switch them, to reduce the wear on the receiver SMA inputs.
For that I’ve chosen the PE4259 SPDT RF switches. They seem to work down to 3.5MHz – as seen in the VNA sweep.
The filters where designed with LC Filter Design Tool from Marki Microwave.
I chose a 3’rd order band pass butterworth topology.
I used fixed value capacitor and adjustable TOKO 10K coils bought from aliexpress. Their Al varies from 8.5nH/N^2 with the core removed, to 22nH/N^2 with the core fully inserted.
The board contains 5 filter blocks that are controlled by a set of 2 SPDT switches. Each set has it’s own ENABLE signal brought to a pin header on the PCB edge.
There’s also a pin header for the power supply. As an afterthought, I’ve tacked a reverse polarity protection diode.
The board is a 4 layer design chosen to simplify routing and to allow for better ground plane coverage.

The board I’ve build has the following filters:
Band | L | C1 | C2 | C3 | C4 | C5 | C6 | C7 | Notes |
3.5MHz – 4.2MHz | 510nH | 1.5nF | 2.7nF | 470pF | 2.7nF | 470pF | 2.7nF | 1.5nF | 5 turns |
6.8MHz – 7.6MHz | 510nH | 220pF | 680pF | 56pF | 820pF | 56pF | 680pF | 220pF | 5 turns |
13.4MHz – 14.5MHz | 330nH | 82pF | 270pF | 22pF | 330pF | 22pF | 270pF | 82pF | 4 turns |
20MHz – 22MHz | 330nH | 56pF | 120pF | 18pF | 150pF | 18pF | 120pF | 56pF | 4 turns |
27MHz – 30.2MHz | 330nH | 39pF | 56pF | 8.2pF | 82pF | 8.2pF | 56pF | 39pF | 4 turns |
The assembly was simple – solder all smd components and then add the coils

Each filter was aligned with a calibrated NanoVNA. For each filter I’ve measured transmission and reflection coefficients:
The isolation is quite good when no filter is selected:
All the documentation is available on github: https://github.com/ealex/hfBandPassFilterBlock