OK, I take that answer...now, why did the FCC go with an ERP as that
would require calculation rather than a measurement. Hard to measure
ERP as far as I know...

Oh well, go figure!

Scott
N0EDV

Dave wrote:

Scott wrote:

So, hows does an armchair operator (one who doesn't have $10K worth of
test equipment) determine the efficiency of the antenna?

Scott
N0EDV

SNIPPED

There are two easy methods and one rule of thumb method that will get
you into the ballpark.

1) As Cecil replied, divide the radiation resistance by the feedpoint
resistance. EZNEC will give a reasonable value for radiation resistance
and an MFJ 259B [~$250] will give a measure of the feedpoint resistance.

2) A freeware program, mobile antenna, will also calculate the efficiency.

3) [Rule of thumb] The gain is proportional to the effective aperture in
square wavelengths. So, as mentioned in another reply, approximately,
the ratio of length of the mobile antenna [~8 feet] to the length of a
1/2 wavelength antenna for 60 meters [~93 feet] yields 8.6% efficiency.
So, 100 watts from an IC-706 [series] yields ~9 watts effective radiated
power. Conclusion, 50 watts ERP on 60 meters with a 9% efficient antenna
would require 555 watts into the antenna.

/s/ DD