![]() ![]() Please note - this table is only a rough guide and includes capacitors and all other components. Table 1 - Recommended minimum voltage separation for given power levels ![]() This is not just some absolute value but includes an unknown quantity of reactance but, in general, the voltage across the input capacitor will be somewhere near the output voltage. The maximum voltage will also depend on what impedance you are going to match. On the other hand, making the coil out of 6mm copper tube is a good idea at any power level but that doesn't mean the voltage separation will allow more than a few watts. The voltage separation may be 300kV but if the coil is made of 0.5mm wire, it will handle only a few watts. The power the tuner will handle is only relevant in terms of the voltage separation and coil resistance (current carrying capability). (Into a dummmy load.) This is less than if a 4:1 voltage balun is used. Overall, insertion loss in tuner MK2 is between 0.1 and 0.15db on 10 metres matching roughly 500 ohms and less on the lower bands using such a setup. Since this tuner does all the impedance matching needed, nothing more than a simple 1:1 current balun is required and strongly recommended. The major power loss in the units described here is by resistance in the wire that the coil is made out of although there will be others. Neither coils nor capacitors consume power so, provided resistive components are kept small, there should be very little loss. Whether you use a T match, Z match or any other kind of matching network doesn't really matter much. If you really must use a long wire referenced to ground, a simple way of using the same output terminals is decribed below. IT IS STRONGLY RECOMMENDED TO KEEP IT SIMPLE STUPID. All of these complications introduce possible losses and possible problems. In the end, the thing stays connected to one amplifier or radio and to one antenna or type of antenna. ![]() Many build tuners and consider a thousand places they can use them and design for all of them. Using coax with a tuner will gain you nothing except a happier radio. The losses are too great using a tuner with coax so it is recommended to include a simple balun (details below). ![]() I have tuned my HF antenna to 70cm but only as a test. Normal use will be HF and perhaps some circumstances in VHF bands. Things to look out for - possible problems identified in design variation. Very brief description giving only the basic idea. Now that a number of people have built them and provided feedback, several things to look out for have been identified. By comparing them, you should be able to construct a tuner to your own particular requirements. This page details several T-match tuners. But if the antenna is too short (resonates above your desired frequency) then it's a little more trouble to add wire to each leg to bring down its frequency of resonance where you want it.VK5AJL - Make your own HF-VHF antenna tuner.Note: To avoid cutting the wire, I usually just fold back each end of the antenna wire on itself and tape it tight if it's insulated wire - or twist it back on itself if you are using bare wire. If the antenna is too long (resonates below your desired frequency) then it's not a problem: you just trim each leg a little at a time until you reach lowest SWR.NOTE: if you start by giving the calculator your *desired* frequency of operation, the inverted V - when installed in its final position - may be still end up too short or too long, depending on the environmental conditions mentioned above. The influence of the ground conductivity and dielectric constant becomes an increasing factor.The resonant frequency of the inverted V is lowered (see the theory behind this at the bottom of this page).As the two sections of the dipole are lowered below the feed point, the angle between the two legs decreases: The angle below the two sections of a horizontal dipole is 180 degrees. In the case of the inverted V we must add - to the list of environmental variables influencing the half-wave dipole - the angle between the two legs of the inverted V. It is adjusted to take into account the special characteristics of the inverted V. The formula used by the calculator to compute the wire lengths for the inverted V is based on the formula for a half-wave dipole. Will give you some leeway to trim the wire ends back if the inverted V resonates too low for your purpose when installed in its final position. Than that of a dipole at the same desired frequency of operation. Calculator above will give you a wire length for the inverted 'V' which will be about 4% shorter ![]()
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