Re: RD16HHF1 in the uBITX #ubitx

Jerry Gaffke

Allison, thanks for the insights.
Much appreciated.

I noticed that the push-pull IRF510's performed much better in simulation using the WA2EBY
output transformer scheme  than with the stock uBitx output transformer. 
Is that the "simplified transformers" you refer to?
Or do you suspect the uBitx has significant trouble in how it drives the IRF510 gates?

My simulation showed that both the WA2EBY and uBitx loaded down the 4x2n3904 driver
with about 12 ohms at 30mhz (still in phase on the WA2EBY, as I vaguely recall).
Rather surprising, but perhaps that was due in part to the simulation using worst case IRF510 spec's?

Any suggestions on how best to pick up gain in the driver and predriver, 
perhaps swap in a different transistor?
We've got lots of uBitx's out in the wild now, and would be nice to have an easy hack.

Jerry, KE7ER

On Wed, Feb 21, 2018 at 03:19 pm, ajparent1 wrote:
The problem is the amplifier has matching issues from simplified transformers.  Additionally 
at 30mhz the AC  gain of the driver and predriver transistors (2n3904) is about 10 as compared
to an AC gain of 20 at 14mhz. So you seeing two problem one of driver that diminishes with
frequency and matching that is less than optimum with increasing frequency. 

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