(5) If you want to turn the receiver oft before the programmed off time, push the TIMER CLEAR button.
To set the sleep timer, proceed as fellows:
(1) Turn the POWER switch OFF, and set the function switch to the SLEEP position.
(2) Push the MINUTE switch once. This will cause the sleep time to count back from the 59 minute mark by one minute. Holding the MINUTE button down will cause the time to change rapidly, in the same manner as described earlier. If you set the display to 40, the receiver will stay on for 40 minutes, then shut off.
(3) If you want to turn the receiver off before the programmed off time, push the TIMER CLEAR button.
While a complete discussion of the physics of shortwave radio signal propagation is will beyond the scope of this manual, some guidelines are presented below to help the shortwave listener to choose the optimum listening frequency for the time of day and the time of year in which you are operating. This discussion will also help you when you are reading the schedules of overseas broadcast stations; you will soon be able to know instantly why you cannot expect to hear Tokyo on 3.9 MHz at 1 :00 in the afternoon.
Shortwave signals are transmitted 6y huge stations running many thousands of watts of power. Their antenna systems are elaborate and expensive. But all of this equipment would be useless were it not for a property of the ionosphere (a layer of the atmosphere high above the earth) which causes signals to be reflected back to earth when they strike the ionosphere.
Depending on several factors, including the time of day, the time of year, and the current state of solar activity (determined primarily by "sunspots"), the optimum frequency for reflection over a particular distance will change. Another aspect that can be noted is that, for s particular frequency on which you are operating, the distance over which signals will be propagated will change. Thus, in order to hear stations 12,000 km away over a long period of time on a particular day, you will likely have to change your operating frequency (consistent with the broadcast station schedules!) in order to take advantage of changing propagation conditions.