Radio wattage vs range

Discussion in 'General Electronics Chat' started by Razor Concepts, Oct 31, 2012.

  1. Razor Concepts

    Thread Starter Senior Member

    Oct 7, 2008
    What is the relationship between the output power of the radio and the range of the signal?

    Say I have a 1 watt transmitter that has a reliable range of 1 mile. Now upgrade it to 10 watts, by what factor should the range be increased by?
  2. bertus


    Apr 5, 2008
  3. russ_hensel

    Distinguished Member

    Jan 11, 2009
    But if you use the inverse square law you should not be far off in most cases.
  4. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    RF data link range (greater than LOS) is a complex subject because it's involves more than just the ERP of the transmitter. The receiver ,antenna, modulation type, propagation and background noise are more important than absolute power. That said we did have some 40kW HF transmitters and directional arrays to burn a signal path off the ionosphere when needed.
  5. Papabravo


    Feb 24, 2006
    On some days my signal goes a few hundred miles. On other days it takes the long path to the other side of the world. I don't think you can come up with a simple calculation that covers it. On the 6M band in the summertime I have a pipeline to Florida and Texas courtesy of Sporadic E-skip which is among the least understood propagation modes. I'm also getting into FSK441 Meteor Scatter propagation - talk about hit or miss communications.

    I spend more time building and using directional resonant antennas than I spend building large amplifiers. Does that give you a clue about bang for the buck?
  6. KJ6EAD

    Senior Member

    Apr 30, 2011
    3.16 according to the inverse square law but that's an ideal without consideration of the many practical factors.
  7. K7GUH


    Jan 28, 2011
    Measure it and see.
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Depends on the antennas involved. I remember reading the transmitter from the lunar module was like 25 Watts and could go from moon to earth, but the antenna array picking up the signal was massive.
  9. JMW

    Active Member

    Nov 21, 2011
    I had a 6watt transmitter with 40 feet of 7/8 heliax connected to a 12 db gain antenna. transmitted to a geo synchronous satellite with no problems. The Voyager series of satellites beat this on a regular basis.
  10. WBahn


    Mar 31, 2012
    If the ONLY variable that is at play is output power, then in many situations the inverse square law should provide a useful guide. But there are many other factors that can nullify that. For instance, if your signal is propagating through a duct of some kind, increasing the power won't increase the length of the duct in any meaningful way. But since you are talking about distances on the order of a mile, these other factors should be much at play for you.
  11. JMW

    Active Member

    Nov 21, 2011
    If you are referring to the little "family" series of radios, you MAY find a small difference between 1 watt and 5 watts. The VHF series have 1 watt the UHF 2. If you were to buy a commercial 5 watt VHF, you may get to 3 miles. Again all depends on many variables. Power line noise, open field or water vs urban NYC environment. Weather conditions such as fog or heavy rain or snow will influence UHF. A useful analogy would be to place a 2 watt night light bulb in a window. If you can see the light, you can probably talk. Windows, and wood frame homes are transparent. Concrete may act as a mirror, or more probably a blanket.
    However the USCG states that they can receive a 1 watt signal on Channel 16, 25 miles at sea. And these are "nautical" 6000 foot miles.