What is a Remote Antenna Tuner in Amateur Radio?
What is a Remote Antenna Tuner in Amateur Radio?
Antenna tuners are used to match the output impedance of the radio to that of the antenna. Most modern radios have built in automatic antenna tuners. But the range to which these built in antenna tuners work is often limited and if there is a high VSWR (voltage standing wave ratio) you may need an external antenna tuner with a higher tuning range. Modern radios have a protective mechanism by which the power output is cut down automatically to reduce damage when the VSWR is high. External antenna tuners are useful when there is no internal antenna tuner or when some types of antennas like G5RV or end fed Inverted L Multi-Band Antennas are being deployed.
Most of the hams use an external antenna tuner directly before the radio as it is quite convenient and can be kept indoors. But an important drawback of an antenna tuner near the radio is that even though the VSWR between the radio and the tuner is low, that between the antenna tuner and the antenna can be high. This becomes quite significant when there is a long feedline, more so at higher bands, when the feedline VSWR is high. An often quoted example is that a 20m feedline which gives a 0.6 dB loss at 7 MHz, can cause 11.6 dB loss at 28 MHz! But the loss on 21 MHz which is an odd harmonic of 7MHz, may be only 1.6 dB.
An obvious solution is to have a remote antenna tuner near the antenna so that it can lower the VSWR in the feedline between the antenna tuner and the antenna. But the drawback is that you to have it high up near the antenna, which would mean that it has to be weatherproof and obviously much more costlier! An additional power line needs to go all the way up to the antenna. There are sophisticated remote antenna tuners with digital controllers to be kept in the shack. You may find remote antenna tuners being mentioned on the qrz.com pages of many hams. But the high power versions may cost almost like your radio while the external antenna tuners to be kept in the radio shack will be cheaper.