I've finally concluded a couple of months testing various combinations of toroid cores and transformer windings, and settled on what appears to be the optimum configurations for my location (and transformer building ability). The antennas are NOT ideally situated (not high enough and to some extent obscured by trees and buildings). I'm not claiming one design is better than another - sometimes, the differences were well within the margin of variation between different builds of similar configuration - but the trend of measurements during testing led me to choose the following. Transmitters: ZachTeck MidPlus (200mW) Feedlines: 25' DX Engineering 400MAX Low-Loss Coax Homebrew EFHW antennas: 12-AWG solid copper clad steel wire length cut for lowest SWR within 15kHz (below) the band's WSPR frequency -- 40 METERSn (7038 kHz) -- TRANSFORMER 3-core 43-mix 72.25:1 [64:1 17-turn] transformer ANTENNA ~66' wire sloped 6' to 20' pointed ~North SWR 1.06:1 -- 30 METERS (10138 kHz) -- TRANSFORMER 3-core 52-mix 72.25:1 [64:1 17-turn] transformer ANTENNA ~46' wire sloped 6' to 20' pointed ~Northwest SWR 1.06:1 -- 20 METERS (14095 kHz) -- TRANSFORMER 3-core 52-mix 49:1 transformer ANTENNA ~33' wire sloped 6' to 15' pointed ~South SWR 1.00:1 Map is of reception reports on 40 meters over 24-hour period from January 26, 2020. (the forum software only allowed for one picture - I have maps for 30 and 20 meters also)