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Old 22nd Jul 2019, 9:20 am   #14
russell_w_b
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Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
Default Re: Aerial for old valve sets.

On HF transmitters the balanced feeders were often 'pinched in' or 'spread out' so the feeder became part of the matching section. It would start out as (say) 328 Ohms Zo at the sender and, if there was a mismatch over the band, or bands, larger than fitted beneath a two-bob bit on a Smith chart, lengths would be adjusted for a different Zo so the transmitter saw the correct impedance and maximum power transfer was effected.

The impedance at the aerial was thus transformed to the DPZ of the sender. We often ran >2:1 VSWR but the unbalanced power was the one to watch.
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