TO: ALL WOOD COUNTY EMERGENCY COMMUNICATIONS AMATEURS
ALL NON-WOOD COUNTY EMERGENCY COMMUNICATIONS AMATEURS
FROM: KEN HARRIS WA8LLM
WOOD COUNTY EMERGENCY COMMUNICATIONS INCORPORATED
WOOD COUNTY BULLETIN NR 14.28 DATE: July 13, 2014
SUBJECT: EMERGENCY COMMUNICATIONS AND TUNERS
During emergencies, as emergency communicators, we may be required to use the HF Amateur Bands for national, state, or even local communication. 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 mis-conception, a tuner is not used to "BLOCK" high SWR from entering the output stage of a radio and "Blowing the finals". The tuner is designed to transform the impedance mis-match between the 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 SWR 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 SWR. 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 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, they do fool the radio into thinking it is putting its signal in to 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 is now 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