TO: ALL WOOD COUNTY ARES MEMBERS (OFFICIAL)
ALL ARES AND NON-ARES AMATEURS ANYWHERE (INFORMATION)
FROM: KEN HARRIS WA8LLM ARRL DISTRICT 3
EMERGENCY COORDINATOR WOOD COUNTY EMERGENCY COMMUNICATIONS INC.
WOOD COUNTY ARES BULLETIN NR 18.27 DATE: July 8, 2018
SUBJECT: EMERGENCY COMMUNICATIONS AND TUNERS
Duping emergencies, as emergency communicators, we may be required to use the High Frequency or HF Amateur Bands for national, state, or even local communications. For those who have HF capabilities or intend to have them, you should consider owning an antenna tuner. Without a doubt, using an antenna that is resonant on the frequency of operation is the best, but it is almost impossible to cover, with ease, the entire portion of every band without one.
Contrary to the fashionable misconception, a tuner is not used to "BLOCK" high SWR or Standing Wave from entering the output stage of a transmitter and "Blowing the finals". The tuner is designed to transform the impedance mismatch between the antenna system and the output of the radio caused by the reactive components that exist in the antenna system. It is this mismatch in impedance, caused by the reactive elements resulting in high SWR on the line between the transmitter and antenna that causes possible damage to the output stage of a transmitter.
One myth that will not go away is the thought that all reflected power is lost and that antenna radiation efficiency is determined solely by the value of the SWR. This is not true, all reflected power is returned by the antenna tuner back to the load antenna. The only reflected power lost is due to line attenuation and this loss is usually insignificant on the HF bands. The antenna efficiency is determined by the two variables of mismatch and line attenuation. To determine efficiency based only on SWR is meaningless.
The use and explanation of an antenna tuner is based upon sound scientific calculations. If one must insist upon a tag, yes, the tuner does fool the transmitter into thinking it is connected to a good antenna. In the days before solid-state, all transmitters employed an antenna tuner built as a necessary part of the transmitter. Only in recent times has the tuner been removed from the transmitter and now is termed as an "accessory". During emergencies these much needed accessories will make a significant difference in our operating capabilities.
Ken Harris WA8LLM
Wood County WV