I spoke with Tony Brock Fisher K1KP about his amplifier. He said the QEX article was
about a year old compared to the technology he is now using but he does not have a new
presentation put together. I am going off telephone notes so I will give it to you raw.
He said he has a 1KW "linearized" amplifier in operation using class D current
mode RF amplification and class D PWM modulation. Key to the performance with class D are
GaN devices. He is using 2 X GS66504(GaN systems - $13)150W devices for the RF and
C3M0120090 (CREE -$7 devices) for PDM modulation. He is getting 10 meter performance out of these things. Mouser stocks both.
A LM5114(
http://www.ti.com/lit/ds/symlink/lm5114.pdf) is used as a driver for the finals.
He says they work at 10 meters but they do get hot. GaN Systems recommended these
devices. Previous use of IXD614 drivers failed above 40 Meters but this is a longtime well known
problem.
To drive the LM5114 he uses 2 Analog devices dividers(no number yet) to develop the IQ
signals. He had an interference issue with the AD part that caused the amplifier to run
at 1/2 frequency when using class E. That is now solved by using class D.
The GaN stuff works very well in RF service as they generally have much lower gate
capacitance than silicon types. There were some reports of parasitics on the GaN
reflector but he has not had any problems with parasitics.
DSP/SDR processing is done on board with a dedicated board. One IQ signal is used for phase, the other for amplitude. Most of the signal distortion that was corrected was phase distortion. This method seems to be similar to the ANON and HPSDR pure signal type of processor.
I have sent Tony another email to get some further detail/clarification on a couple of points. More later.
Ashley
