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