12VDC @ 100ft from source

[jeeep]

I need to light a cluster of leds at varying distances; 50ft, 75ft, 100ft. The cluster of leds would be atop of an antenna and at the bottom would be several switches that controls the cluster. Idealistically, I would like to have 24VDC at the bottom of the antenna and then step the power down to 12VDC at the top to power the leds. But I know with these varying distances the higher up the power runs the lower the voltage will be (is this a correct assumption?). So what would be the best way to supply a constant 12VDC at the top of the antenna?

[Omni]

Obviously, you have enough voltage at the base (24V) and the length to the LEDs (100') max is well within the tolerance of your supply voltage.
Consider using an adequate guage wire (16AWG) and place a small regulator circuit at each interval (length).
Using a regulator at each node 50', 75' & 100' will regulate the voltage to the desired amount required by the LEDs.
The regulator does not need to be too technical, a simple Zener (1W) along with a proper sized load resistor will work.
Furthermore, perform a test on the ground to make sure your interval regulators will operate properly.

Example:

Stretch the max length of wire on the ground and at each interval place a regulator, the latter will allow an easy painless way of testing your setup.
Twist the wire for more integrity along with a clean installation and use a decent wire (teflon coated/silver).

Remember, the NEC does not even begin to calculate a voltage drop until 100' in reached.
However, in your case the max would actually be 200' since you must also factor in the return length.
Furthermore, a calculation is not really necessary since you are 100% above the required voltage at maximum length.

Footnote:
I remember awhile back designing advanced accelerators for the Trans-Atlantic cable.
Most common people believe solid state amplifiers are placed on the ocean floor to amplify the communication signals since the length is extremely long.
In truth the latest engineering design consisted of specifically placed 3 meter lengths of doped Rare Earth erbium (fiber optic) that would continually accelerate the transmission.
Rare Earth Erbium is located deep within the Earth and when doped with the proper elements is highly light sensitive!

[jeeep]

Omni, thank you very much for your post. It contained everything a perfect reply should consist of: an explained solution, an example with insite, and a interesting/relevant footnote.

[hotwaterwizard]

Have you ever seen low voltage lighting in someones yard?
They run over 100 feet and they do not use regulators at each junction.
They use a large wire. You could ground the negitive to the tower and run one wire up to the lights.

Voltage Drop Calculator

http://www.powerstream.com/Wire_Size.htm

http://www.csgnetwork.com/voltagedropcalc.html


LED info
http://www.quickar.com/ledbasics.htm