What are the collectives thoughts on the type of material to use for a
homebrew ATU enclosure, should it be aluminium to reduce unwanted RF
radiation or plastic to reduce coupling effects possibly caused by an
aluminium enclosure.

Regards Simon.

Simon,
Why worry about the extremely minute amount of radiation from small tuner
coils and components when this is hopelessly swamped by radiation from the
nearby antenna, even from the back of a beam, and there's always some
significant amount from the feedline.

Think in terms of relative magnitudes.

The amount of radiation depends only on one dimension, ie., the physical
LENGTH of what may be imagined to be radiating. Imagination is the keyword.

There is hardly any significant difference in radiation from a tuner between
a plastic box, a metal box, and no box at all.

I prefer no box. Stray capacitance is smaller. A metal box behaves as a
shorted-turn around the coils and results in power loss. And it's nice to
be able to see the position of the roller coaster and the tuning capacitors
without the tedium of unscrewing all the screws in the cover.

There may, of course, be a slight advantage of a box, metal or plastic, in a
dusty atmosphere or if you are, like me, a nicotine addict.

Alcohol addicts will automatically ignore this mild advice anyway.
----
Reg, G4FGQ

On Sun, 06 Feb 2005 15:23:44 +0000, Reg Edwards wrote:

Simon,
Why worry about the extremely minute amount of radiation from small tuner
coils and components when this is hopelessly swamped by radiation from the
nearby antenna, even from the back of a beam, and there's always some
significant amount from the feedline.

[snip]

Exactly. Well said Reg. I have seen a beautifully working 1KW antenna
tuner constructed on a breadboard. Completely open and very nice to look
at also. No TVI. No interference. Save yourself the hassle and expense and
build it without an enclosure at all (as long as your pet cat doesn't like
to wander around your shack while you operate!).

Larry VE7EA

On Sun, 06 Feb 2005 08:25:38 -0800, Larry Gagnon wrote:
On Sun, 06 Feb 2005 15:23:44 +0000, Reg Edwards wrote:

Simon,
Why worry about the extremely minute amount of radiation from small tuner
coils and components when this is hopelessly swamped by radiation from the
nearby antenna, even from the back of a beam, and there's always some
significant amount from the feedline.

[snip]

Exactly. Well said Reg. I have seen a beautifully working 1KW antenna
tuner constructed on a breadboard. Completely open and very nice to look
at also. No TVI. No interference. Save yourself the hassle and expense and
build it without an enclosure at all (as long as your pet cat doesn't like
to wander around your shack while you operate!).

Well, the OP did not specify whether it'd be installed at the shack
or at the antenna.

Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK

What are the collectives thoughts on the type of material to use for a
homebrew ATU enclosure, should it be aluminium to reduce unwanted RF
radiation or plastic to reduce coupling effects possibly caused by an
aluminium enclosure.
====================
For QRP power levels it could be best fitted in a wooden box , simple and
easy .
For much higher power levels a metal enclosure will be better.
However ,in order not to influence inductances by the metal cabinet , a rule
of thumb says that (air) inductors should be free form any metal keeping a
distance of their diameter
Example : With a fixed air or roller inductor of say 100 mm (4 inches)
,you need an enclosure of at least 300 mm (12 inches) such that the inductor
is not less than 100mm from any metal surface.

For this reason many homebrew antenna matching units are fitted inside
non-metallic enclosures often made of perspex (plexy glass)

Frank GM0CSZ / KN6WH