[hpsdr] Erbtec Amplifiers

[FRANCIS CARCIA]

Hi All,
I have found an issue with the Erbtec amplifier strip when trying to run at 48 volts and over 100 watts output. The feedback resistors in both the driver and final are too low a value. I verified this searching through motorola data and applications. At 200 watts carrier I can open a final resistor in a minute or so and melt the solder connections of the driver resistors. Motorola data shows the MRF148 uses a 470 ohm resistor. I changed the 100 ohm resistor to a 330 ohm 2 watt. It just fits in the space. I'm going to change the final feedback from 25 ohms to 50 ohms. 
I started with a -25dB IP3 at 100 watts running 48 volts. The new driver feedback resistor and a bigger shunt inductor core has me at around -32 dB IP3 (mil method) I see by the waveforms on the final gate that the driver is working hard to drive the 5 ohm input loads of the FET gates and overcome the 25 ohm feedback resistors. 
I'm getting close to 300 watts output with the 25 ohm FB resistors 160 through 6M. The IMD is down to around -20dB IP3 due to the distorted drive waveform. This should improve with 50 ohm feedback resistors. 
Thank You Hans, DL2MDQ for your test data and beautiful pictures. 
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