TO: ALL ARES OPERATORS IN DISTRICT 3 (OFFICIAL)
ALL AMATEURS IN WEST VIRGINIA (INFORMATION)
FROM: WOOD COUNTY EMERGENCY COMMUNICATIONS INCORPORATED AND WOOD
COUNTY AMATEUR RADIO EMERGENCY SERVICES (ARES)
ARES DISTRICT 3 BULLETIN NR 07.31 DATE: August 5, 2007
SUBJECT: EMERGENCY COMMUNICATIONS AND TUNERS
During emergencies, we 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 virtually 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 VSWR from entering the output stage of a radio and "Blowing the finals". The tuner is designed to transform the impedance mismatch between the load, which is the antenna and transmission line, 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 Standing Wave, on the line between the transmitter and antenna which could cause possible damage to the transmitter's 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 mismatch 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, they do fool the radio into thinking it is seeing a perfect 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.
Reprinted, with modifications of, Wood County RACES Bulletin NR 92.06, By Duane Jones, N8LDM)
Ken Harris WA8LLM
Wood County WV
WV ARES Assistant Section Coordinator
WV ARES District 3 Emergency Coordinator