[hpsdr] HPSDR finals
carcia at sbcglobal.net
Thu Jan 17 17:33:34 PST 2013
I have been chasing the IMD monster for a while now. The first thing I needed to do is adapt the MIL method of measuring IMD because that is what you see in the RX. The 6dB gift method is a poor interface to the super clean Penny / Hermes exciter.
Tiny transformers do not produce good IMD. Type 61 cores running at less then 150g and 3 Oe is a good starting point.
TLT transformers work much better than the brass tube primary transformers. I'm very close to -30dB IP3 at 300W PEP.
At 20 Watts I'm around -40dB IP3. I'm running 3 stages of push pull FETS, MRE136, MRF148, MRF150. The first tuo stages are running class A. There is a good chance I can eliminate the MRF136 stage because most of the time I have 15dB of pads between Hermes and the amplifier. I'm also working on a 1200 watt modified MRI amp with 4 SD2932s. The IMD still needs work but it is on the air. Predistortion sounds very intereting. Frank WA1GFZ
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