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Actually, I would prefer to rewind the
transformer with a center tap, and eliminate the chokes, feeding
the DC to the center tap.
Z for L8, L9 should be >> then the output impedance which
looks like the antenna impedance for the 1:1 transformer.
I am adding a 70 watt amplifier to my uBitx, so I just need 5
watts out on all bands to drive it. I doubt I will do much more,
on the transmitter, but I will have to see how the amp behaves. I
may to to better equalize the output level between the bands.
On 4/19/2018 2:37 PM, Jerry Gaffke via Groups.Io wrote:
resonance helps us to a point, though an ideal inductor would
generally be better.
For example, if the inductor is self resonant at 14mhz, we'd see
much more power out on 20m
than we see on 10m. I'd prefer to keep gain vs freq somewhat
controlled and predicatable.
The caps are easier to add, easier to obtain, have a higher self
Maybe add 220pF caps across all six of the 22 ohm emitter
resistors, and forget the inductor?
Then add a variable cap somewhere around Q90 that can be tweaked
to give the flattest response,
that setting may vary given your particular 2n3904 transistor
But the inductor in series with the negative feedback is a good
If this can all be done with just 3 extra components and get good
enough results across
the different uBitx's out there, I'm fine with that.
One other issue:
As Henning notes in post 45035, the chokes L8 and L9 are best
wound on a single core:
See the discussion below figure 4 on this webpage, where he
discusses how the bifiliar
approach works, though he does not discuss the individual choke
I was seeing significantly worse results in how the uBitx final
to the WA2EBY final in my LTSpice simulation, could be due to
I may have to play with that further, not obvious to me how or if
the individual chokes
at L8, L9 would impact the results..
On Thu, Apr 19, 2018 at 11:00 am, Jerry Gaffke wrote:
It's a parallel resonance: