Thursday, August 16, 2012
a 3rd order 6m band pass filter
I upgraded the 6m filters in my ARRL Homebrew Challenge 3 radio entry, a 6 & 10m SSB/CW radio.
Shown here is the 3rd order 6m bandpass filter that is placed behind the LNA & driver, the purpose of this filter is to reject the noise image from the LNA and to provide some filtering on the output of the exciter.
I found that it was necessary to use air-core inductors because they provide high Q, each inductor had to be 90 deg (or close as possible) to each other to reduce coupling, and each stage was shielded from each other. With this configuration the filter performance was within 0.5 dB of simulation.
It was tough to find shielded enclosures with compartments. I found that Teko makes excellent shielded enclosures and these can be ordered in small quantity.