QTX 475 kHz
|output V over 50Ohm ~72W Rf at input 76W (25Vx 3A) N=96% ! ?|
|V drain puls|
had to modify the total capacity of C2+C3 to 10+6.8+6.8 nF
and the output C4 6n8 + 6n8 to archive maximum output.
But at 25V still could not produce 100W out
I did change R4 to 1k because of latching problems I had earlier that cost me a few IRF's
Drive level increase does not change the output in this class D type switching mode.
The Flex1500 XVTR/C port 0dBm at level 30% is sufficient.
Also the K3 XVTR out level was perfect to drive the QTX.
Class D is perfect for CW WSPR modes.
The Drain pulse form seems correct.
Optimising L3 for maximum output did not bring more output. Po drops as soon as a ferrite bar is approaching L3.
I would expect that L3 could be increased when dropping the frequency from 500 to 475 kHz
After re-arranging C2 C3 C4
The output increased to 75V/50Ohm 112.5W50Ohm dummy Bird 8251
C2+C3 is now 10n+ 6n8+ 4n7
The C4 original was 6n8 now increased to 9.9n
At DC input power I=5.23A at 23.5V =122.2W n=92%
There is a bit more heat developing in L3 the IRF540 is a bit warm.
The high efficiency is amazing.
The SWR power meter now points at 45 never reached that level before
it was only "12" in 2010 when WD2XSH/17 2-way WSPR succeeded