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K6TAR

Joined: Sat, Apr 4th 1998, 00:00 Roles: N/A Moderates: N/A

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Output impedance coupling for LDMOS (2) mono band amplifiers Dec 4th 2021, 00:18 2 617 on 4/12/21

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Output impedance coupling for LDMOS (2) mono band amplifiers K6TAR on 4/12/21
What one sees with multi band pair of LDMOS device amps output circuit is a balanced impedance transformation (usually a Guanella 4:1 or 9:1) device followed by a choke type 50 ohm balun. So far so good. Looking at mono band amplifier layouts for 6M and 2M. Looks like the balanced to balanced Guanella and following balun can be changed to a quarter wave transformation and choke type balun all occurring in one piece of coax. There is a wide range of intermediate impedance level coax types of the TC series to meet the needed impedance. Will this work? Or is transformation from say 4 ohms to 50 ohms at some power level (say a mirror image pair of MRF300 devices) more than is practical with a quarter wavelength transformer? Or is an alternative plan to go balanced to balanced with a 4:1 Guanella, followed by combo quarter wavelength transformer and choking to kill off currents on coax braid exterior (i.e., make balanced to unbalanced) a better plan to finish up with 50 ohm output?

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