How do I determine how much power to input to a dipole antenna, when I know the range? I've heard 1/4 watt can transmit for a mile, but how do you get that without practical experimenting?

 

Learn to use a Path Loss Calculator like this one.

You have to consider frequency, TX and RX antenna gains, coax losses, TX power, RX sensitivity, and distance for starters

 

And there are other variables including time of day, season of the year, and position in the 11-year sunspot cycle. Right now we are supposed to be at the Solar Max, but sadly ole Sol is not cooperating.

 

Thanks Mike, you seem to know a lot about radio and you've been a huge help to me lately! Another question though, as far as transmission lines go. If I have a transmitter circuit, running at 900MHz, that leads straight to the antenna, should I take the output of the circuit and connect it to an RG8X coax cable? What kind of connector do I need at 900 MHz? Should I use a different type of cable?

 

Usually there is at least a short length of coax between a transmitter or receiver and its associated antenna. At 900MHz, I would be looking at BNC,TNC or SMA connectors.

Don't forget that an antenna needs to approximate a center-fed 1/2 wavelength dipole; a 1/4 wavelength monopole without a ground plane (or the other 1/4 wavelength of the dipole) is a crappy antenna.

 

Thanks a million Mike! You're a huge help