On Mon, 08 Mar 2004 17:02:07 GMT, Richard Clark
wrote:

For the unbalanced probe, the throat cross section should show
1 by 0.5 wavelength dimension.
The mouth cross section should show
2 by 2 wavelengths.

The probe is situated on the face of the wider dimension, thus its tip
penetrates to the middle (where two diagonals would cross). The
illustrations are clear to this matter even though the dimensional
description is a bit rocky.

tnx f ur reply kb7ghc

0.5 wavelenght seems like a intuitively reasonable choice for the
smaller dimension of cross section of the throat / waveguide part. If
the tip of the probe (=1/4 wavelenght antenne rod?) is very close to
the opposite wall it is hard to imagine that it would not affect the
function and the SWR (which, unfortunately, I lack equipment to
measure)

But are you sure that 1 wavelenght is the optimum value for the other
dimension of the cross section? That is more than in the examples I
have seen on the net.

Is there some reason for choosing a 2 : 1 ratio of the two dimensions?

I may add that in the first horn I made, the dimensions were 0.36 x
0.72 wave. It worked, but probably not quite optimallly (I lack real
measuring equipment.) I then tried to put the antenne rod
perpendicular to the SMALLER side instead, but that did not work at
all (very weak signal).

73

Jeppe (former OZ3FV, hav'n't renewed my licence for about 30 years :-(