Re: RD16HHF1 in the uBITX #ubitx
Gordon Gibby <ggibby@...>
The old fashioned solution for capacitive loading was simply to put an inductor in parallel tuned to the desired frequency, to cancel it out.
In my ancient vacuum tube rigs, they do that in the driver and final amplifier stages, and I get about the same power all the way from 80 meters through 15 meters, and in some rigs through 10 meters.
Maybe they were on to something? Perhaps there is a way to take that technique and apply it to semiconductor systems with some semiconductor switches to adjust component choices?
From: BITX20@groups.io <BITX20@groups.io> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Thursday, February 15, 2018 12:41 PM
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx
As reported here: https://groups.io/g/BITX20/message/40938
an LTSpice model of Q90, Q911,Q912, Q92,Q93,Q96,Q97
shows that with the IRF510 gates clipped free of the circuit,
the signal available to the final in volts is about 77% at 30mhz what it is at 7mhz.
Power available is down by the square of the voltage, or about 60%.
LTSpice is probably assuming worst case 2n3904 parameters.
This result will not be fixed by going to RD16HHF1's.
With the IRF510 gates tied back in, the drop in signal became much more pronounced
due to capacitive loading by the IRF510's. They need to be driven harder for good results at 30mhz.