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| - | ====== "L" Network vs "T" Network ====== | ||
| - | **From Ten Tec Reflector June 5, 1998** | ||
| - | There is a reason why the T network tuner has enjoyed more popularity than an L network tuner like the #238 2KW roller inductor tuner that we presently build. | ||
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| - | First, the advantage to an L network tuner as opposed to a T: | ||
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| - | Because there are only two variable components, there is only one setting of each which will provide a perfect match to a given load | ||
| - | impedance, and this unique setting automatically provides the lowest network Q possible. Low Q means low circulating currents, hence low loss, and it also provides the widest frequency bandwidth of operation before re-tuning is necessary. | ||
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| - | Since the inductor is always parallel, the L network always provides a two-pole lowpass response to provide harmonic rejection. | ||
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| - | In English: You can more easily achieve a 1:1 SWR with an tuner other than an L network, but is more likely you're dissipating RF | ||
| - | output within the tuner itself. The T network is not as broadbanded as an L network. | ||
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| - | The reason the L network, despite its' distinct superiority to a T match, does not enjoy wider use is this: The L network requires | ||
| - | two configurations to match all possible antenna loads. One, for impedances greater than 50 ohms, requires the capacitor to be | ||
| - | across the antenna. The other, for load impedance of less than 50 ohms, requires that the capacitor be placed across the transmitter. Keeping in mind that any SWR other than a perfect 1:1 match indicates a load impedance that could be either above or below 50 ohms, you will need a switching system to reverse the configuration of the tuner (which is used in the #238). | ||
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| - | The T network is more widely used due to a misconception about what constitutes an efficient match between transmitter and antenna. | ||
| - | An SWR of 1:1 is meaningless if there is no efficient transfer of RF energy to the antenna system. The T provides easy matching | ||
| - | capabilities, and is a simple circuit to construct and use. | ||
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| - | The switching system we use in the #238, in concert with fixed capacitance, allows 5 different tuner configurations. We refer to the #238 as a "modified L" for this reason. Our web site has a picture of the tuner, simple schematics of the configuration possibilities, and a more detailed description as well. Between the #229 and its' newer brother #238, we have been manufacturing this "modified L" tuner for 18 years and are well satisfied with the performance. | ||
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| - | I've said this before and I will say it again: No antenna tuner, ours or anyone else's, will match 'any' load impedance on 'any' band at 'any' power output. The important decision, when purchasing an antenna tuner, is to accurately assess your needs and to have an idea of what value of load you are trying to match. A little reading in the ARRL Handbook or the ARRL Antenna Book will give a wealth of information for this. | ||
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| - | Sincerely, | ||
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| - | Scott E. Robbins, W4PA | ||
| - | Amateur Radio Product Manager | ||
