effective radiated power

Just show him the calculator on this site

Should do the job.

Arfa

Lenny-

Charles' method should work for you. If a customer asks, you need to know more about the antenna's gain - is it compared to an isotropic antenna (dBi) or compared to a dipole (dBd)? Note that 0 dBd = 2.1 dbi. An antenna with isotropic gain of 8 dBi would have a gain of 5.9 dB with respect to a dipole.

The isotropic gain is useful for calculating field strength at a distance, but gain with respect to a dipole is easier to measure!

Fred

The calculator that I pointed Lenny at does it for dBi and dBd. A lot easier to just show your customer something that goes ahead and does the job, rather than faffing about in front of him with a calculator, working with a formula and numbers that you're not totally easy with ...

Arfa

That is true, but I assumed that he asked this such that he could re-familiarise himself with the math so that he would be able to demonstrate to his customer how to work it out. Based on my many years of dealing with customers, and making myself look dumb on occasion by trying to explain something that I was not properly familiar with, I just felt that it might look slicker to the customer to be able to just enter the figures and see the results, for both comparison schemes, instantly shown. If he really wants to go down the route of doing it all himself, Google will turn up many hits if he just enters " Antenna ERP " as the search string.

Arfa