Richard Harrison wrote:
Page 345 gives the surge impedance in ohms for a balanced antenna as:

Zo = 276 log 1/P

Bailey`s graph on page 345 gives dipole impedances from 70 ohms to 680
ohms for rod peripheries from 1 wavelength down to 0.00001 wavelength

Is the graph impedance looking into 1/2 of the dipole?
276 log 1/0.00001 = 1380 ohms, just about double the 680 ohm value.
--
73, Cecil, http://www.qsl.net/w5dxp

Cecil, W5DXP wrote:
"Is the graph impedance looking into 1/2 of the dipole?"

I only quoted from the plot for tthe whole dipole in free-space.

The graph on page 345 has two traces:

Zo, or antenna average surge impedance, ZA, for a balanced, center-fed
dipole in free-space, which is found to be a function of the antenna
thickness=

ZA = 276 log 1/P

The other formula is also plotted. It is for a vertical rod against
ground. It has exactly 1/2 the resistance of the dipole.

For peripheries larger than 0.25 wavelength, Bailey notes that surge
impedance departs from the formula. For smaller peripheries, the plots
are almost straight lines on the scale used. Peripheries are plotted
with log spacings. Impedances are plotted with linear spacings.

Best regards, Richard Harrison, KB5WZI