I may have found the reason why the MMIC LNA pre-amp did not work well on the magloop. I’ve been reading an old paper by Chavdar Levkov LZ1AQ, who has been very active in this area for quite some time, and has an interesting website.
The paper is at
http://www.lz1aq.signacor.com/docs/f..._loop_engl.htm, but I’ve put in to Word, and done a bit of highlighting, and that’s attached. On page 11, the question of balance is addressed and point arises that you need to have a transformer in the output of the pre-amp, and the LNA (as supplied) does not have that. So, it looks like it’s not matching problem but a balancing one
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B