Re: LPF frequency curves #lpf

Daniel Ekman SA2KNG
 

On Wed, Dec 27, 2017 at 10:19 PM, Bob Sutton via Groups.Io <zl1rs@...> wrote:
... but aren't the harmonics from the Si5351a already >10dB down on the fundamental, so the over all spurious emissions after the 40dB suppression of the LPF are already much greater than the 43dB required by your USA regulations?

The output from the synth is squarewave-ish, driving different PA designs in the qrp-labs product line, so not looking the same after amplification. on top of that we have coupling in the pcb, grounding and cables that leaks a bit more of the higher order harmonics past the filters.

That said, who knows what questions/problems may have arised if this optimized filter was the design in the qcx (:
If/when I rebuild my U3S to include the 5W PA, I may try these designs in the LPF modules as they're a lot easier and cheaper to mess with rather than on the qcx. Also ordering the latest design on the relay-switched board.

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