Hi, I am looking for information on a concept I am writing software for. Since I don't know much about EE, I though I'd get suggestions. I wanted to know that best setup I could use for a short range point to multipoint broadcast. The example I have is go-cart racing. Suppose you are racing around a track with 2 other drivers. You wanted to be warned when someone was in proximity to you. If you were leading in the 'red' car and the 'green' car came withing 1000 feet (arbitrary) of you, a dash light (green in this case) would light up. When the 'green' driver moves out of range, the light goes out. If the 'blue' driver moves in range then the blue dash light comes on. If they are both close, both lights are on. I assumed at first the simple fix would be to use 3 different waves (bands), one for each driver (assuming you the red car were behind the others), but that could end up requiring an unreasonable amount of hardware. I instead will use the device as a carrier wave for code that will identify the car behind. (much like a garage door opener is coded) For starters, I wanted to know: What band range do I need to work in assuming the distance is less than half a mile or so? What do I need to keep the signal from being omnidirectional? (I wanted it to be a relatively focused forward beam.) That's all for starters. I have more questions, but they will be based on the solutions given. I have attached a drawing (forgive me, I am not trying to insult your intelligence, I just thought it would be clearer) Thank you so very much.