Hi Dave,
Are you referring to the balun inside the dummy aerial? If yes, I have initially constructed the dummy aerial as in the top circuit (balun in between single-ended L-network & preamp) in the linked image below:
The above arrangement conveniently allowed the use of a single-ended L-network, but had a couple of issues: 1. the balun altered the L-network output impedance, and 2. momentary un-levelling of the test source during frequency sweep.
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Consequently, to overcome the aforementioned problems, the dummy aerial was subsequently changed to the bottom circuit which I had initially resisted because it requires a balanced L-network.
73, Leong, 9M2LCL, ex-9W2LC.
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