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 BULLETIN NR 16.42 DATE: October 16, 2016
SUBJECT: EMERGENCY COMMUNICATIONS AND TUNERS
During emergencies, as RACES or ARES operators, we may be required to use the 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 virtually impossible to cover, the entire portion of every band without one.
Contrary to the mis-conception, a tuner is not used to "BLOCK" high VSWR (or Standing Wave) from entering the output stage of a radio and "Blowing the finals". The tuner is designed to transform the impedance mis-match between the load (antenna) and the output of the radio caused by the reactive components that exist in the antenna system. It is this mis-match in impedance, caused by the reactive elements resulting in high VSWR on the line between the transmitter and antenna that causes possible damage to the output stage.
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 VSWR. This is not true, all reflected power is returned by the antenna tuner 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 mis-match and line attenuation. To determine efficiency based only on VSWR 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 radio into thinking it sees a perfect load. 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
WCEC
Wood County WV