Radio antenna flashing warning beacons do not simply flash on and off. This would be too similar to ground clutter that pilots see all the time, such as flashing red stop lights at four-way stop intersections. To differentiate the radio antenna flashing warning beacon, it has a unique flashing pattern. The light is on for three seconds, then fades towards off for one second, then repeats.
Simple blinking LEDs blink at a 50% duty-cycle - half on, half off - and blink much too fast, usually once per second. Most flashing circuits don't provide the option for anything other than a 50% duty-cycle, even if the rate is adjustable. So both of these are inappropriate for use to realistically model radio antenna flashing warning beacons. These also leave the fading issue unresolved.
To use MasterFlasher to model a realistic radio antenna flashing warning beacon, we first need to adjust the rate of the MasterFlasher to the proper rate. We want the unit to repeat on a four second cycle, so we need to set the Base Rate Jumpers to 1110, for a period of 240 sixtieths of a second, as shown in Table 2 from the MasterFlasher article.
Next we need to get a 75% duty cycle. We can get the proper duty cycle by combining two outputs at different rates. If we use output jumper 16 for one positive output, and output jumper 8 for the second positive output, we get the first two outputs below. If we then add them using 1N4001 diodes, we will get the third waveform below, which has a 75% duty-cycle, just what we need.
Finally, we need to add the fading during the off period. We can do this by using a capacitor to hold some voltage to light the LED during the fading period. As we want the LED to fade slowly, a large cap, together with the LED current limiting resistor, will form a simple RC circuit and do this for us very easily. With a VLED = 5 volts and a current limiting resistor of 150 ohms, we find that a 1000 uF capacitor provides the proper fading characteristic. Combining all this, we get the following circuit, which provides a very realistic simulation of a radio antenna flashing warning beacon.
Try it! You'll be amazed how much more realistic it looks than a flashing LED.