On Sat, 17 Dec 2005 23:38:13 -0500, "J. Mc Laughlin"
wrote:

I have dealt with approximations of the subject device. In each case,
an extremely high input impedance amplifying device is placed at the base of
the antenna that has a known voltage amplification and a 50 ohm output
impedance. Knowing that a close approximation of the open circuit voltage
is amplified by a known amount, a calibrated, tuned voltmeter (at 50 ohms)
is able to measure the size of vertically polarized E (with the usual
uncertainties). (and a bit of arithmetic)

Hi Mac,

I too, will jump in with alternatives to this short, thin rod feeding
an infinite Z. It makes for a simple specification, but when the
frequency begins to climb such is not very practical. Input Z's tend
to be dominated with strays and that "short" rod begins to become
enormous. Such artifacts of the MF era are quickly discarded.

The NIST methods (NIST technical note numbers 1309 and 1098) employ
resonant sized dipoles feeding a DC Hi R (and hence AC Hi Z load) at
the gap of the elements. By DC Hi R, the detector filter employs
50KOhm components in a balanced cascading filter that in turn feeds a
Hi R voltmeter through 250KOhm leads (carbon impregnated plastic
conductors to decouple both loading and induction).

Uncertainty, worst case, is 1dB.

Schelkunoff's algorithm is used to find the length of the dipole (no
real surprise here for halfwave length). The effective length is not
half, but rather closer to 62 - 63%.

73's
Richard Clark, KB7QHC