Re: bitx output harmonics
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John, The two section low pass filter is a standard across a number of transceivers build and sold in the USA. Our harmonic suppression is just within the legal limit. Here is the scan as I had performed when we finished the layout.? The difference between my and Wayn's scan results is probably due to overdriving of the power amplifier that clips and distorts the waveform. With Wayn's modification, you can be sure that even if you overdrive, you will still be within the legal limits. A simpler fix is to just back off the sliver coloured preset near the driver transistor until the point where the transmit power starts dropping. That is the point power beyond with ?the compression and distortion increases substantially. You are safe within that limit. - f On Mon, Feb 20, 2017 at 7:42 AM, John Smith via Groups.Io <johnlinux77@...> wrote: I used a 100pf ceramic 50V cap that tested out to be 87pf. It did not blow up. But I have no way of testing it. I'll just have to trust that the second harmonic solution will keep me legal. It was that, or a 120pf testing at 115pf. Does anyone know what it actually takes to suppress the second harmonic frequency adequately? Or is this close enough to do some good? |
