So you will find that we have now gone from 7 pages of instructions to 32+ pages (with some helpful hints). When I set out, I decided to photograph everything, as well as re-write the instructions. Now if you have arrived on this Website looking for some decent instructions, then you have come to the right place. It does work and due to space restrictions, I am using a 21m resonant Dipole with an 80m 3watt Transceiver and achieving 1:1.3 SWR with this tuner. I am glad I did as I learnt some things on the way. Now I have had my say and I will state that I took it as a challenge to complete the project and get it working. In fact I think I got more fun out of trying to work out the original words or sentence meanings than building the kit. I say almost non-existent, as in most cases, there are no instructions from most suppliers, you have to do a lot of googling to find the instructions, and when you do, you get about 7 pages, mainly written in Google Translated Chinese to English. What lets this kit down however is some of the errors in the kit parts, and the almost non-existent instructions. It is in effect a T-Topology Antenna tuner. The design is actually quite simple, building on some existing designs and reference documents such as. The price ranges from $8.00 through to $60 (discounted □ for the same group of components. This little QRP (low power) Antenna tuner has been around for a while and it is sold as a Kit from Aliexpress, Amazon, Ebay, Banggood to name a few. QRP Manual DIY Antenna Tuner Kit 1 -30Mhz QRP Manual Days Antenna Tune Tuner DIY Kit 1-30Mhz I also did not incorporate an SWR indicator, since I normally monitor forward and reverse power in my station with a dual-section Bird wattmeter.Īlthough this antenna tuner has served me well for many years, I am replacing it with a homebrewed microprocessor-controlled autotuner with expanded (160 meter) frequency coverage. In the version shown here, I used a tapped inductor (instead of a roller inductor) to facilitate rapid bandswitching. Thousands of homebrew antenna tuners have been based on the Ultimate Transmatch design. However, computer simulations have shown that the T-match must be used carefully, since for low impedance loads, especially, it can absorb large fractions of the transmitter power. The T-match is an extremely versatile circuit, capable of matching almost anything (hence the "ultimate" in the name). The 4:1 output toroid inductor is mounted just behind the tapped inductor, and is switched into the circuit by the Jennings RB2 vacuum relay, which is mounted on a bracket to the rear panel. This interior view shows the dual split-stator (250 pF/section) Millen 16250 capacitor on the left, and the 200 pF Millen 16520A capacitor on the right. This improvement results in less voltage stress on the toroidal transformer since it always sees 50 ohms at its input, although it has the disadvantage that it is in the circuit at all times, even with unbalanced loads. (In the tuner shown here, a Jennings RB2 vacuum relay accomplishes this task.)Īlthough legions of commercial antenna tuners have copied the output toroid idea, the ARRL is now recommendaing a different design (introduced in the 1999 ARRL Handbook), in which the toroid is placed at the input of the network. The user ordinarily strapped the toroid to the unbalanced output of the tuner. The other innovation in the design was the use of a 4:1 toroidal balun for open-wire transmission lines. Subsequent experimentation showed that the split-stator design was not really necessary, and in later designs it was replaced with an ordinary single-stator capacitor. The "Ultimate Transmatch" was based on a variation of the simple T-match, with the input RF fed to the mid-point of a split-stator capacitor. The insulators are spaced for six-inch 600 ohm feeders. This rear view of the antenna tuner shows the RF input SO-239 connector, the output SO-239 for unbalanced (coax fed) antennas, and two high-voltage ceramic feedthrough insulators for open-wire transmission lines. The two indicator lights are controlled by the main station switching console and show whether the tuner is on-line or using open-wire transmission line. The only controls on the tuner are the tapped inductor switch and the two tuning capacitors. Other references can be found in November 1973 QST (page 11), and the 1973 ARRL Handbook (page 583). The circuit proved so popular that it was also featured in generations of the ARRL Handbook from the 1970s. The Ultimate Transmatch was described in the "Beginner and Novice" section of the July 1970 QST (). This homebrew legal-limit antenna tuner is based on the famous "Ultimate Transmatch" introduced by the late Lew McCoy, W1ICP.
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