It uses 100 watts as an example.
Go down the left column and find the gain of your antenna.
This would be 6 db in our example.
Read across to get the watts multiplier....4.....in this example.
Read across to the right of the column and find your answer of 400 watts ERP!
These figures are assuming that you are getting 100 watts to the antenna from the end of your feedlilne and do not reflect any loses in it or the antenna and you know the gain figures for the antenna.

You should see that with every 3db increase, your effectively doubling the ERP.


You can calculate any power input to your antenna by just using the watts multiplier to get your answer.

HERE'S ANOTHER GOOD...... SIMPLE EXAMPLE (With a bit of Ham Humor thrown in)

10 watts into a 3db gain, 2 meter 5/8 wave mag mount on the roof of your mobile.
 
It's a Ford, built in 1994, V8 engine, automatic transmission with 198,000 miles on it and you still owe 18 payments of $287.57 after refinancing a year ago.

The oil needs changing and it has 4 new tires and you discover the battery is dead!

To Calculate the correct ERP answer you had better replace that battery first so can check your power output into your antenna with your watt meter to make sure your rig is putting out that 10 watt signal to the antenna.

During the process of finding and replacing the battery, you have spent 4 hours finding a ride, getting past the crowds at Wally World, buying the battery, getting back home, finding the right tools and you can't find them because you loaned them to your teenage son for bike repair, disturbing your neighbor to borrow the tools, helping him take his grill outside, opening the hood, bursting the water hose, destroying the battery clamps, cutting your fingers, asking your neighbor to take you back to Wally World to get new clamps, water hose, and antifreeze, discovering that you spent all your cash for the new battery, going to the bank, back to Wally World, getting the new parts, installing them, cranking the Ford only to discover that the XYL ran it out of gas, borrowing a gas can from your neighbor, walking to the gas station around the corner, putting the gas in, starting the car, closing the hood and discovering that you did not tighten the hose, antifreeze spewing all over the new battery, smoke pours out of the alternator, sparks fly and the engine dies!

You throw up your hands, call a wrecker, tow it to your friendly auto repair shop and after a grand total of $487.50 later, not counting the cost of the battery, parts and gas..... you get the car, fire up the rig,
key the microphone.............no output!
Is Ham Radio Fun or What!
 
NOW BACK TO THAT SIMPLE EXAMPLE
10 watts verified on a repaired 2 meter rig ($187.50)Antenna gain (on the F-o-r-d) of 3 db..........
Read down the chart in left column, find 3db.........
Get multiplier of 2.1 in next column to right...........
Multiply 2.1 times your 10 watts going to that 3db gain antenna sitting on top of that............Ford!
2.1 x 10 = 21 watts ERP!
Just think about how much gain that would have been on a Chevy!

Editors Note: Use caution while on Hamuniverse due to our Humor Filter Malfunctions from time to time! Have fun!