Final Measurements:

I added 8 more radials this evening for a total of 16.

Radials 2:1 Fo 2:1 BW Z VSWR @ Fo

8 3460 3564 3801 341 40,0 1.2 (at antenna)

16 3524 3580 3800 276 31,0 1.7 (at antenna)

Fo is the resonant freq, 2:1 are the lower and upper 2:1 vswr frequency
points.
BW is the 2:1 SWR Bandwidth in Khz.
Z is the R +/- j impedance read from an MFJ-269 antenna analyzer at the
feedpoint.

Since the radiation resistance of the antenna is known to be 25.4 ohms:

Efficiency with 8 radials: 25.4/40 = 63.5% or ground loss = 1.97 dB
Efficiency with 16 radials: 25.4/31 =81.9% or ground loss = 0.86 dB

Additional info, 2:1 VSWR Bandwidth in Khz:

0 Radials = 580 khz
8 Radials = 341 khz
16 Radials = 275 khz

So, both "traditional" considerations of a 1/4 wave vertical have now been
satisfied:

Increasing the number of radials decreased the feedpoint Z, approaching the
nominal 25.4 ohms radiation resistance of the antenna.

Increasing the number of radials from 0 to 8 to 16, narrowed the bandwidth
from 580 to 341 to 276 khz respectively.

The SWR at resonance is worse with 16 radials than with 0 radials (higher
ground losses mask the reactance at the feedpoint)

16 Radials over very good Iowa black loam yields an efficiency of
approximately 82%, and I see no reason to further increase the number of
radials to recover .86 dB...and of course, it would probably require
doubling the radial number yet again, to 32 to get half way there.

I'm now satisfied that the antenna behaves as expected and that the numbers
are credible, but not absolute.

Time to play on the air some more. So far it is getting out very well.

Thanks to all of you for your input, I've learned a lot by playing. The TLE
on-line calculator is a jewel! EZNEC 4.1 got me in the ballpark. The three
most valuable lessons learned: beware of an unintentional 1/4 wave
transformer (coax); Reg's clever formula for calculating radiation
resistance of an inverted L, using simple trig functions, and 16 radials on
80m are quite sufficient OVER MY TYPE OF SOIL.

....hasan, N0AN

"Reg Edwards" wrote in message
...
Hasan,

If you download program ENDFEED and insert details of your antenna and
ground radials system, you will find the impedances closely agee with
what you actually get. (I'm always very happy when this happens.)