HF antenna tuner 80-10m without range switching
With this antenna tuner almost the entire SW range can be covered without range switching. It need to tune so only the two rotary capacitors be operated, you must therefore no area switch more actuated. However, the rotary capacitors must be dual designs, such as those earlier were f.e. used in broadcast receiver constructions. It should be noted that the one capacitor must be mounted isolated from the chassis. For this I used insulating nipples as they are used for the mounting of TO-3 power transistors on heat sinks. This can be seen on the last picture, wich shows the bottom of the device.
The circuit goes back to the building proposals of PA0FRI, which he published as FRI-Match on his website. I have extended the circuit by the three-step switch. With this input and output can be reversed, furthermore, the entire tuner can be switched off with it. As variable capacitors I used brand new specimens from Chinese production, each with a maximum capacity of 2x 365 pF. The coil (13 + 6 + 6 + 6 turns) is wound with insulated 1mm installation cable on a piece of 16 mm diameter PVC conduit (type EN16). For the taps, the plastic insulation of the coil wire is melted away in the corresponding places, for what e.g. a worn soldering tip is suitable.
Immediately after commissioning the circuit, I was surprised by the ease of use and the good features of the circuit. PA0FRI has by no means promised too much on his website. At all amateur bands in the range of 80m to 10m I managed to match almost any different wires to the transmitter output of my transceiver. The tuner can be easily pre-tuned by first setting to maximum noise when receiving. By alternately adjusting the capacitors, the VSWR can almost always be set to values of 1.5 and better. If this is not possible in the standard position of the switch (low impedance), the switch position with reversed input and output (high impedance) quickly helps to achieve good VSWR values. Incidentally, in this mode, with appropriate antenna wire lengths, better radiation can be achieved, as with the often propagated and widely used combination of antenna tuner and 1: 9 transformer (so-called Unun), without the latter being required. That would only bring in additional losses anyway.
For example, with this tuner I can also use my 10m groundplane on the longer wave SW bands. Below the 20m band, I achieve the clearly better results, if I separate the shield of the coaxial cable by unscrewing the PL connector from the antenna connector of the tuner, so that virtually acts as an additional long wire antenna. For this purpose, the shield should not be grounded. This does not affect the function of the antenna on 10m, as known the electromagnetic ground are here the Radials. When screwed PL connector, I can make 2m operation in switching position bypass with likewise good SWR with the same antenna. The 10m antenna then acts as a λ-5/4 radiator.