Re: RD16HHF1 in the uBITX #ubitx
Gordon Gibby <ggibby@...>
Didn't realize he has L3 in there. I have the boards and parts somewhere and may eventually get around to building it!
This would form a series circuit (to AC ground) with the gate-source capacitance. In series circuits as the frequency nears resonance the voltage across individual components SOARS. I haven't evaluated where he chose to put resonance but this may
be a compensatory effort.
Experimentation often beats out simulation.
From: BITX20@groups.io <BITX20@groups.io> on behalf of Henning Weddig via Groups.Io <hweddig@...>
Sent: Thursday, February 15, 2018 2:47 PM
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx
Gordeon, please have a lok on the "famous" WA2EBY amp. He is using inductors in series with teh gate-bias resistors. My explanation is that this inductor of unknown value together with the gate-souce capacitance of the IRF 510 forms a parallel resonator,
i.e. cancelling out the high gate capacitance. This may be the reason why he gets a flat(er) frequency response as shown in part 2 of his paper.
In addition: the driving transistors hav e arelativly low ft, they must roll off.
LTSPICE simualtion of the bidi amp show a gain reduction of about 1 dB at 45 MHz, but for the driver stages in teh transmitter section things my be a bit different.
Simulation will schow!
BTW: I can confirm that the audio preamp in the receiver clips in reallity (on my BIOTX40) at output voltage swings as LTSPICE predicted.
Am 15.02.2018 um 18:58 schrieb Gordon Gibby: