80m Transmitter Ver X2

[NZ0I]

The 80m transmitter section of the Ver X2 hardware boards is alive. It appears to be putting about 2W into a 50-ohm load when 9.2V is supplied to the final output FET. I am not yet happy with the waveform being delivered to the dummy load: it is an obviously distorted sine wave. I'm confident it would not pass spectral purity tests at this point. But it is a start.

The schematic design has been modified to reflect lessons learned thus far. The driver section was modified on the X2 board to use a totem pole driver configuration, which seems to work adequately. But a search of Digi-Key turned up some FET drivers that modeling suggests will work even better. So the updated schematic includes an SI5134 FET driver. 

Also, I discovered that the 80m signal amplifiers and driver will consume significant power for as long as 12V is supplied - regardless whether the transmitter on the air or not. So I added a load switch that can completely remove power from the 80m amplifiers allowing off-the-air battery life to be extended.

Experiments suggest that tweaking the power FET's gate resistor value, and of the output filter component values, will probably be sufficient to achieve a clean output signal on both the Ver X2 boards and the new 80m transmitter design incorporating the SI5134. The schematic includes footprints and test points that should help with troubleshooting and optimizing the circuit. The latest transmitter schematic is available via the OpenARDF web site, or using this link: https://drive.google.com/open?id=0B9STTH26Cx2FX3dRTEtIUmlEUlk

Parts arrived today that I hope will allow similarly encouraging results for the 2m transmitter section.