Still working on it
Still cranking away at the LDMOS amplifier I am getting 150 watts out still. I'm now optimizing each section.
Posts
A few changes
Made a little more progress on the LDMOS amplifier. I added 4200pf of capacitance to one part of the output circuit and picked up some output power. Now I'm getting 150 watts out at max power. Half way there
A little bit of progress
I made a little bit of progress on the LDMOS amplifier. I got the output raised by about 10 watts with the same drive level. Headed in the right direction...
More RF testing
Doing a bunch more testing on the LDMOS amplifier. So far, not making a lot of progress getting past 300 watts.
Amplifier rebuilt
The LDMOS amplifier is rebuilt and working. I replaced the resistor, transistor, zener diode, and arduino. I added a current limiting resistor to the small transistor. I'm getting 100 watts out. That's 1/3 of my goal. But it looks like it is doing well. Drive is 394 mW. Current is 2.59 A. If I calculate the efficiency correctly, the amp is 79.99% efficient in it's current state.
The Magic Smoke escaped :(
The Magic Smoke escaped :( I played with the negative feedback today. I started at the minimum of 500 ohms, where ~500mW gets close to 50 watts out. Then I turned the drive down on the radio to show 10 watts output. I reduced the negative feedback by increasing the resistance. I turned it up just a little bit and the power output came up significantly. Somewhere around 50 watts with the same drive level. I turned it up a little bit more, I think the power got near 100 w atts, but I don't recall exactly. Then it started to smoke. The Resistor R21 in the High Voltage Mosfet Switch section (330 ohms to ground) started smoking. At the same time, the status LEDs went out and the LCD went out. The fuses didn't blow. The mosfets don't appear to be shorted either. My guess is maybe the MPSA42 transistor shorted and took out that resistor, and the voltage regulators went into short protection mode and cut off all of the power. I'll have to do some more investigating of the comp