Re: The new uBITX boards are here

Ashhar Farhan
 

The load on the Mosfet gates is of 130pf in parallel with the gate resistor : 220 ohms in this case. The reactance of the gate capacitance would be about - j50 towards, the higher end of the HF spectrum. Paralleling a resistor with the the gate produces a load impedance for the push-pull driver. As Allison noted, our driver chain does not have enough juice at the higher end of the spectrum, the higher impedance decreases the drive requirements. I came upon the 220 ohms experimentally. I tried values from 10K downwards. More than 1K rested in in-stability. The output starts tampering off below 1K and rapidly so below 470 ohms. I tabulated the results inthe logbook. I don't have access to it now.
- f

On Mon, 28 May 2018, 06:06 Kees T, <windy10605@...> wrote:
I think the 27 ohms has more to do with 50 ohm input impedance matching.

73 Kees K5BCQ

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