User manual LDG ELECTRONICS AT-897 VERSION 1.1

[. . . ] Press the Tune button on the front panel of your AT-897 tuner until the red LED comes on, then immediately release. You're ready to transmit 3 Features · · · · · · Automatically matches antennas from 6 ­ 800 ohms impedance, or a 10:1 SWR Very low current consumption: 300 mA during turning, less than one microamp in standby, or can be turned off completely. Uses latching relays, to retain tuned setting indefinitely even when power is completely removed Powered by the FT-897 through the CAT cable (provided); no external power source required CAT port access provided Tunes in less than 8 seconds, usually around 4 seconds Specifications · · · · · · · · · · · · · · · Microprocessor controlled, switched L tuning network Antenna impedance: 6 to 800 Ohms (Approximately up to 10:1 SWR) Continuous coverage 1. 8 to 54 MHz 200 fast memories Latching Relays hold tuned setting indefinitely, even when power is removed Tunes nearly any coax fed or unbalanced input antenna. Use optional Balun for long wires or balanced input antennas Mounts directly on the side of the Yaesu FT-897, provides side feet attachment Dual function tune control button ­ Tune or Bypass Power rating HF: 0. 1 to 100 Watts Provides CAT port access Tuning time: 1 to 8 seconds, 4 average Power requirements: 10 to 15 volts DC @ 300 mA during tune Operating voltage supplied via the FT-897 CAT/Linear Port (cable supplied with tuner) Enclosure sizes: 11. 5" x 3. 25" x 1. 5" Weight: 2 pounds 4 Getting to know your AT-897 Your AT-897 is a quality, precision instrument that will give you many years of outstanding service; take a few minutes to get to know it. [. . . ] The tuner will switch to bypass; RF from your FT-897 transceiver will go directly to the antenna with no matching. A word about tuning etiquette Be sure to pick a vacant frequency to tune. However, do your best to avoid interfering with other hams as you tune. Your AT-897's very short tuning cycle, usually only a few seconds or so, minimizes the impact of your tuning transmissions. 9 Theory of Operation Some basic ideas about impedance The theory underlying antennas and transmission lines is fairly complex, and in fact employs a mathematical notation called "complex numbers" that have "real" and "imaginary" parts1. It is beyond the scope of this manual to present a tutorial on this subject, but a little background will help you understand what your AT-897 is doing, and how it does it. In simple DC circuits, the wire resists the current flow, converting some of it into heat. The relationship between voltage, current and resistance is described by the elegant and well-known "Ohm's Law", named for Sir George Simon Ohm of England, who first described it in 1826. In RF circuits, an analogous but far more complicated relationship exists. However, the presence of capacitive and inductive elements cause the voltage in the circuit to lead or lag the current, respectively. In RF circuits this resistance to the flow of electricity is called "impedance", and can include all three elements: resistive, capacitive, and inductive. Capacitive Reactance Inductive Reactance The output circuit of your transmitter consists of inductors and capacitors, usually in a series/parallel configuration called a "pi network". The transmission line can be thought of as a long string of capacitors and inductors in series/parallel, and the antenna is a kind of resonant circuit. At any given RF frequency, each of these can exhibit resistance, and impedance in the form of capacitive or inductive "reactance". Transmitters, transmission lines, antennas and impedance The output circuit of your transmitter, the transmission line, and the antenna all have a characteristic impedance. For reasons too complicated to go into here, the standard impedance is about 50 ohms resistive, with zero capacitive and inductive components. When all three parts of the system have the same impedance, the system is said to be "matched", and maximum transfer of power from the transmitter to the antenna occurs. While the transmitter output circuit and transmission line are of fixed, carefully designed impedance, the antenna presents a 50-ohm, non-reactive load only at its natural resonant frequencies. At other frequencies, it will exhibit capacitive or inductive reactance, causing it to have impedance different from 50 ohms. When the impedance of the antenna is different from that of the transmitter and transmission line, a "mismatch" is said to exist. In this case, some of the RF energy from the transmitter is reflected from the antenna back down the transmission line, and into the transmitter. If this reflected energy is strong enough it can damage the transmitter's output circuits. The LDG design uses banks of fixed capacitors and inductors, switched in and out of the circuit by relays under microprocessor control. A builtin SWR sensor provides feedback; the microprocessor searches the capacitor and inductor banks, seeking the lowest possible SWR. [. . . ] All returns must be shipped to us pre-paid; we will not accept units with postage due. Please fill out and print the return form from our web site under Support/Manual, then Tech Support-Warranty. If you need to return your unit to us for service, package it carefully, keeping in mind that we will re-use your packaging to return the unit to you. Include a full description of the problem, along with your name, address and a phone number or e-mail address on the web form. [. . . ]