Bandpass Filter for Crowded Setups: Build, Buy or a Little of Each?

You may have heard the sounds before. On your SSB or CW station while operating in a group (Field Day comes to mind), the faint “sssh, sh, ssh” of Morse Code, the sporadic static noise of a digital mode, or the familiar voice of your group member covering up the weak phone or CW operator you’re trying desperately to dig out of the cacophony already present on the frequency. It’s frustrating! I’ve read that there have been nose-to-nose confrontations among the friendliest of hams in these situations. What do you do? Stay home next time? Operate alone? There can be a better solution.

Bandpass Filters

Putting a single or multi-band HF bandpass filter between your rig and antenna can greatly alleviate the situations described above. But multi-band HF bandpass filters can cost what a moderate transceiver goes for, ranging from $600 to over a thousand dollars. And those are just for the 100-watt models. Building is perhaps a cheaper option which requires both time and engineering design skills. But will a homebrew set of filters perform at the level of a known commercial product? What about a middle ground solution in which you build the final product but don’t design or actually build the filter board?

I’ve taken that middle ground, purchasing a pre-built HF multiband bandpass filter (BPF) board from an Australian company, VK-Amps. It needed a build-out into a box with switches, RF connections, and so forth, which I will discuss below. To give some objective basis for evaluating