Update: Homemade ADS-B Filter now with LNA on the same PCB
Reddit user BigReid has posted an update on his PCB based hairpin ADS-B filter. He has now added a low noise amplifier (LNA) circuit onto the same PCB board. BigReid used the LNA design written about on this page. The PCB files are here and the Reddit thread can be found here.
“Ahead of”….. “before”…. “after”… perhaps I could petition for less ambiguous or relative terms like “antenna side” or “radio side” ?
As of the picture in the post, left side is antenna connection, while right side (LNA output) is the receiver (RTL-SDR) connection.
as it seems, it is vice versa. The Input goes into the LNA and is followed by the microstrip filter.
100% agree! The driving force behind the design was the filter, the LNA (I guess I should just call it an amplifier) was more of an after thought. It’s there to help overcome coax loss.
I’ll comment that a microstrip filter in front of an LNA turns it from an LNA into a ho-hum small-signal amplifier, because the insertion loss of the filter is added directly to the noise figure of the LNA.
Now, it turns out that for ADS-B, you don’t need really-good noise figures, so in this particular case, no harm. But in the *general*
case, any LNA with a filter in front of it is suspect, unless the filter is extremely low loss ($$$). One “trick” that I have seen is
use a silver-plated cavity resonator as part of the input matching circuit to an LNA, which produces stunning results, but not at budget prices.