On 01/11/2011 10:34 AM, Richard Lamprey wrote:
> Greetings from Kenya. I've saved up a few questions for the network,
> perhaps someone out there can help.
>
> 1. New regulations here dictate that we must now all fly with 406
> ELT, and especially recommended is the Artex 406 (PLBs will not do
> here). This requires that for composite aircraft, the skin of the
> aircraft must have radial metallic strips, 1 inch wide, in the shape
> of a 6-point star, extending out for 24 inches in all directions.
> Seems a bit excessive for a Europa, where can we find that space?
> Behind bagage bay is obvious best bet. Will alumnium strips work (I
> have sticky aluminium tape, 2" wide). Has anyone fitted this arrangement?
I had the Artex 406 ELT fitted in my aircraft (until an adaption of the
regulation made the use of a certain PLB possible, and I replaced the
Artex by a PLB).
The Artex was working fine though. I had it placed on an aluminium mount
directly behind the bagage bay D-panel, with the antenna inside the
fuselage on top of the Artex-unit itself, connected via a short coax cable.
It took some work to get the mount to double duty as a ground plane for
the antenna. I had to install ONE(!) radial which I tuned on 121.500
MHz. The radial is a 1/2 inch strip of aluminium with drilled holes in
it. The whole setup is sturdy but light weight.
(For the technically interested reader: the tuned radial is an
acceptable trick. Instead of a ground plane of random dimension, you can
use ONE thin straight "ground plane" strip, provided you tune it to a
specific length. As seen through the eyes of the Artex, the antenna is
now no longer a 1/4 wave on a ground plane, but a center fed 1/2 wave.
Although it looks very different to the human eye, technically it is
similar to the COM antenna in the tail, which is also a center fed 1/2
wave without ground plane. I used the original Artex antenna for this
setup as one "half" of the antenna. The Artex sees a 50 ohms impedance
and is perfectly happy with it, as its diagnostic test indicates. To be
even more correct, the antenna also needs to be in tune at 406 MHz. This
is achieved by giving one leg of the mount the correct resonance length
for 406 MHz.)
I think this is the best solution. The aluminium mount works as a "shock
absorber", and by mounting the antenna on the unit itself, it gives the
best chances that in a fuselage scattering crash the unit and the
antenna don't get separated.
If you are interested, I have the mount still lying on my bench, and I'm
willing to ship it if you care for the shipping costs. I can also
photograph it, but to fit the thing in the curved fuselage I had to
shape everything to fit, and it is hard to describe exactly the angles
and curves of the aluminium, and if you reproduce it chances are that it
won't work unless you have the tuning tools and experience yourself (but
in that case you weren't asking about it anyway).
One final comment: The installation calls for a switch with an
indicator, and a connection to a power supply. The external power supply
is ONLY used for feeding the diagnostic LED. It is a shame that this
external power is mandatory, as it requires a non-switched "life" wire,
something you not exactly desire if you are lying in a puddle of fuel
after the crash.
So solve this matter, I installed a resistor of 1K in series with the
power supply. This limits the current to 12 mA, not sufficient to burn
anything or even cause a spark, but enough to lit the LED and make the
authorities happy.
Frans
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