[hpsdr] Pennywhistle IMD

[FRANCIS CARCIA]

Hi All,
Wow -40dB IP3 is pretty clean. I wonder what the IP3 was before feedback was added. I've converted a couple different MRI amplifiers for use as HPSDR finals. I was able to improve things by going to a lower perm core for T2. Presently I'm using 7turns bifilar on a T106-2 iron core at 48 volts on the final. My 3 stage amplifier started with a very poor IMD but have it up to -30 dB IP3 (mil method) at 200 watts out. I have way too much again with 3 stages so use a 16dB worth of pads at the output of Penny. I'll be changing feedback resistors after reading these results. I have seen gain curves of a number of FETs and notice some gain compression as power goes above about 70% which may hurt IMD. Pennywhistle FETs are running low power so IMD will be better. I'm interested in comparing notes with anyone working to improve IMD of FET class AB amplifiers. I'm not sure how well Pennywhistle works on 6 meters but I have found it easy to do 160 through 6 meters
 using TLT wound transformers. Frank WA1GFZ
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