With a reasonable signal at the output of the mixer, the next step is ensuring that only the 144.39MHz tone must be selected and amplified.

The initial measurements of the bandpass filter are as follows, with a rediculus amount of loss in the passband:

Upon simulating in LTSpice (I had generated the filter with Marki Microweave's online filter calculator, and trusted the S-Parameters it generated), it became clear that this filter only works with perfect components. As soon as the slightest amount of ESR is added, it performs terribly.

I tried tweaking the parameters in the calculator and wound up with the following filter:

The 300nH inductors are replaced with 270nH ones because LTSpice indicated it would still work. I will update with more info surrounding this topic.

The new filter displays better, but still unusable performance, as measured by the NanoVNA: