RadioBanter - View Single Post

March 10th 04, 11:11 AM

On Tue, 9 Mar 2004 14:46:46 -0600 (CST),
(Richard Harrison) wrote:
There is no requirement on how small the spacing of a transmission line
can be as long as it doesn`t short where you don`t want it to short.
There is no abrupt minimum spacing for the small dimension of a
waveguide either. As in the longer dimension of the waveguide
cross-section, the attenuation rises as the guide narrows, but it does
not cut off propagation down the guide at 1/4 wavelength as the longer
dimension does at 1/2-wavelength.

I don`t have a catalog at hand but it seems to me that rectangular
guides are about twice as wide as they are tall. This ratio has proved
to work very well.

Tnx a lot for your reply Richard

I have no in-depth knowledge of the physics/mathematics involved but I
think I have gathered by now a meaningfull understanding of how wave
guides work and the importance of their dimensions.

So my problem is really mostly that I am trying to guess how close the
tip of the 1/4 wavelength probe / antenne rod can be to the opposite
wall of the wave guide - without "detuning" the probe / affecting the
SWR in a detrimental way.

As I wrote I have no measuring equipment. I just disassembled the
dipole antenna of a 30-Euro Belkin Wireless USB adapter and inserted
the 1/4 stub into a cardboard/aluminium-foil horn antenna. That way I
do not have to solder anything and there is no extra transmission wire
loss. Crude electronics? I dare say it is. But it helps me share an
internet connection with a friend living half a block away. And it is,
of course, kind of interesting for an old radio amateur...

Jeppe