This is especially true of the internal auto-tuners found in many popular HF transceivers.ģ.2 T-network topology: It is not our intent to go into the mathematics of these networks there is an excellent T-network tuner simulator We cannot simply connect our ladder-line-fed 80m doublet, 40m long, or our coat-hanger, to a T-network auto-tuner via a 4:1 balun and expect it to tune all bands. The limited-range T-network design does not have the matching range to accommodate random-length mobile whips or wire antennas, or non-resonant doublets fed via balanced line. It is designed to match near-resonant antennas such as LPDA’s, multi-band verticals, tri-band beams etc. T-network autotuner considerationsģ.1 Capabilities, limitations and expectations: As mentioned in 2.1, the T-network autotuner is intended to match loads having a maximum VSWR excursion of 3:1 (16 ~ 150Ω resistive) to 50Ω resistive. Odd multiples of λ/8 are recommended, e.g.3/8-wave, 5/8-wave, 7/8-wave etc. It can accommodate complex loads with a very wide impedance range, from tens (λ/4) to thousands of ohms (near λ/2). This type of coupler is intended to match random-length radiators such as whips and long-wires to 50Ω resistive. To increase the matching range, the network can be switched from a Π to an L topology by switching out the output shunt capacitance. The input is connected via a 50Ω feedline to the transceiver, and the output via a short single-wire feeder to the feed-point of the radiator. Its matching range is usually limited to a maximum VSWR excursion of 3:1 (16 ~ 150Ω resistive) to 50Ω resistive, although it can be extended by switching in additional L and C values.Ģ.2 The Π/L-network automatic coupler: This type of tuner consists of a switchable Π-network with capacitive shunt arms and an inductive series arm. The T-network autotuner normally has a coaxial input and output, and is designed for connection to a coaxial feedline.
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