Re: NEC-LIST:Modelling of a radiating coaxial "probe"

Odd you should ask.

In one of the Allerton Antenna Conference proceedings there is a
description of a dipole probe made using semi-rigid coax. Two lengths
of coax are connected to the delta ports, run parallel to each for a
while, and the coax formed into a dipole by two right angle kinks in
opposite directions. The outer is stripped back in the way you
describe. The parallel length is soldered. The one port is
terminated in 50 ohms, and the receiver sees a pretty constant
impedance at the other port as I recall.

There should also be a description of a standard coax probe, which as
I think originated at NBS in Boulder. The outer as I recall is
connected to one or two "bazooka baluns" to reduce current on the coax
screen itself.

There are descriptions in the literature of small shielded loop probes
used by Mo"nich in Germany to model shipboard DF antennas. These
loops terminated in a non-inductive 50 ohm resistor, and had a slit at
the top of the loop. Two small ferrite beads were placed on the two
halves of the loop thus formed to further reduce unwanted shield
currents. (G Mo"nich, "Antenna elements for improved shipboard HF
direction-finding," Proc IEE Vol. 134, Pt F, pp 609-614, 1987, also
"Prediction of bearing errors of vehicular DF antennas by fast
measurements on models," Third International Conference on Antennas
and Propagation, Conf Publ. IEE 219, pp. 101-104, 1983)

Russell, Prof Mo"nich graciously sent me more information, which I am
sure I can track down if you are interested.

Duncan Baker.

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