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

"Bill Turner" wrote in message
...
On Mon, 07 Feb 2005 11:00:46 GMT, "Highland Ham"
wrote:

For much higher power levels a metal enclosure will be better.
__________________________________________________ _________

May I ask why would metal be better than wood?
=====================================
At 1000 -1500 Watts RF it is better to keep thing within metal walls.

As I understand it ,in the USA any amateur radio station operating at an RF
power level in excess of 50 Watts needs to make a 'antenna radiation
assessment'
Although an antenna matching unit is not an antenna , sitting close to a
non-screened matching unit with air inductors operating at 1000 -1500 Watts
RF output ,seems to me rather too close for comfort.
For the same reason RF power amplifiers (even when home brewed ) are no
doubt inside a metal enclosure.

Frank GM0CSZ / KN6WH

sitting close to a
non-screened matching unit with air inductors operating at 1000 -1500
Watts
RF output ,seems to me rather too close for comfort.
Frank GM0CSZ / KN6WH

==========================

The problem lies mainly in the imagination. What measurable harm can befall
you?

A coil of wire in a tuner radiates hardly more than a straight length of
wire of about the same length as the coil former.

Radiation is negligible in comparison with the field from the nearby
antenna, even from the back of a beam, which nobody worries about.
----
Reg.

Reg Edwards wrote:
The problem lies mainly in the imagination. What measurable harm can befall
you?

Well, I can certainly imagine being zapped by high RF voltages!

Of course, that's not the real subject of this thread, but it's
certainly a reasonable practical consideration.

I wonder, if there's a solid material, suitable for construction of an
enclosure, whose electrical properties are more similar to that of air
than those of metal or wood?
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Reg Edwards wrote:
The problem lies mainly in the imagination. What measurable harm can
befall
you?

Well, I can certainly imagine being zapped by high RF voltages!

Of course, that's not the real subject of this thread, but it's
certainly a reasonable practical consideration.

I wonder, if there's a solid material, suitable for construction of an
enclosure, whose electrical properties are more similar to that of air
than those of metal or wood?
--
Doug Smith W9WI
========================

If you insist on an enclosure, next to wind, why not try glass?

Then you can view the roller and capacitor settings without the
inconvenience of taking all the screws out of the cover. It's also easy to
show a next door neighbour the works, calm him down, just after you've
cleared his TVI.

There's only roughly 1000 volts, its RF not DC, around a 1 KW tuner. Fairly
harmless stuff. You can't call yourself a real ham unless you've ever had to
quickly remove the tip of your forefinger from a hot spot.

But don't make a habit of kissing capacitor vanes, attractive as they are,
because they look beautiful in motion!
----
Reg, G4FGQ

Reg Edwards wrote:
There's only roughly 1000 volts, its RF not DC, around a 1 KW tuner. Fairly
harmless stuff. You can't call yourself a real ham unless you've ever had to
quickly remove the tip of your forefinger from a hot spot.

Having got a thumb on 400 volts RF... let me assure you, I'm prepared
to sacrifice some efficiency to prevent it from happening again!
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com