Re: UBITX V3 TX GAIN VARIATIONS
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On Friday, August 31, 2018, 3:11:21 PM PDT, ajparent1/KB1GMX <kb1gmx@...> wrote:
On Fri, Aug 31, 2018 at 12:41 PM, Jerry Gaffke wrote: Allison
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Imma gonna put this here, tho it really does not apply to either the post I'm replying to or the "gain variations" as such If you want to know why the ubitx is generating all the "cruft" in the finals, look at the schematic especially L9 and L10. Both are wound on ferrite cores ..Both have DC current flowing through them ..According to the rev. 4 schematic they are supposed to be 60 uH ...I measured the ones I removed from my radio 23 uH ...just for fun, i monitored the impedance variation through them while passing DC current through them? O ma current, 23 uH ...5 ma current gave 15 uH ...10 ma current gave 11 uH ...since these inductors pass 100 mA (according to the setup procedure ...who knows what the inductance is under operating conditions ...Flowing DC through a ferrite biases the magnetic domains in the ferrite ...Maybe it goes back most likely not....ANY ferrite us susceptible to permeability change under the influence of a DC biasing current ...Its doubtful your "spice" analysis will account for this .. Make the finals look like the WA2EBY unit....Clean up the finals, then go chasing the remaining spurs (there are a few left I noticed)
Jim
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