First you must decide what kind of broadcast are you going to do, a taped broadcast is always the easiest method however live broadcasting could be possible.
Where will you be doing the broadcast and how will you get there? Most mobile set ups are from a remote location in a car or van. You can also broadcast from a tent, out house, airplane, boat, etc. Use your imagination but be sure to consider the following objectives.
1. You must have an adequate power supply for your equipment. Choose an area that has access to AC power, or use a battery operated tape player and a transmitter equipped for 12 volt DC car battery power. If your transmitter won't run from 12 volts DC, then you can buy a DC to AC inverter that hooks to your cars' battery, be sure it can handle the amps required by your radio (some older tube-type radios require up to 500 amps!). Inverters can be purchased from RV dealers and camping retailers. When running from your car battery, be sure to keep the motor running! Radio equipment will drain your battery very quickly. You may find that your equipment will not operate from your cars' DC output.This may mean that your cars' alternator does not produce the amps required, this can be remedied by installing a new, more powerful alternator, but it is expensive.
2. Find a location that you can safely set up your station. This means don't trespass, and avoid locations that will arouse suspicion. The terrain can also play an important role, if you are in a valley your signal may not get out as well as you would like.
3. Make sure you have a safe place to erect an antenna, Avoid stringing wires near power lines! You can use one of the popular HAM radio automobile antennas or you can erect your own dipole or other antenna if you have available supports. If you have a tree nearby you can use it for a very effective support for your antenna. A good way to get the wires into the trees is to use a sling shot to launch a weight tied to 50lb test fishing line across the top of the tree, the line can then be tied to the antenna and pulled to the top of the tree.
4. Provide a good ground for your equipment This may require going to the location in advance and pounding a copper rod into the ground.
5. Set up your station in a manner that will allow you a quick exit if needed. Choose a place that provides a good view of the entrance and at least two exits so you will be able to spot trouble and escape before it arrives.