rampil wrote:
>
> Come now Ron,
>
> Don't you remember the total lack of noise on my radios also?
> I have a Whelan comet flash too.
Because of the discussion about strobe noise, I got slightly worried so
I decided to test my setup, which was just finished. I was particularly
worried since I have a high power strobe, with one strobe bulb on the
fin, just a short distance away from the antenna...
So, today was strobe testing day.
I have an AVI-PAK strobe power supply, probably the most powerfull
strobe unit available (51.5 joules / 70 Watts).
Mounted under the ceiling just behind the D-panel.
I have three strobes: one on the fin, and two at the wingtips. The one
on the fin gets the most power, it alternates with the wingtip strobes
which share the power together.
Radio is a Garmin (Apollo) SL-30, plus a Vertex handheld.
Antenna is home-built, mounted in the fin, quite similar to the
Europa-antenna, but just a little bit more broadband.
The wiring for the strobes: From the strobe power supply directly via
the top to the fin. For the wingtips, the wiring goes via the back of
the doors to the rear wing pin, where I have installed a connector.
The rest of the cables of the airplane (including coax) are located on
the bottom.
Results:
Strobes at full power did not break the squelch. Neither on the Garmin
SL-30, neither on the Vertex handheld radio.
Next test was with squelch open. Strobe system was not audible at all.
NAV system (VOR and glidescope) could not be tested as there is no VOR
within receiving distance.
So far I'm happy with the result. :-D
I think the key of all this is:
1) Proper shielding of the cables. All strobe lines are shielded at the
housing of the strobe power supply, and nowhere else (also not at the
end near the strobe bulbs).
2) Keeping the setup symmetrical (hence the location underneath the
center of the top).
3) Keep coax and strobe cables as far as possible separated.
4) Ground and power leads for the strobe are not shared with anything
else. Even the navigation lamps (same housing as strobes) have their own
power leads, which follow a different routing than the strobe cables.
5) Make sure the antenna is tuned properly, and the coax cable properly
RF-decoupled.
About the latter: I have the coax cable run through torroids near the
antenna, and near the rear bulkhead I have some of the cable tightly
coiled up (ten turns) on a lightweight 5cm plastic tube. This to block
any RF travelling on the outer part of the coax. This blocks radiation
inside the airplane, and also reduces sensitivity for noise generated
inside the airplane. I think decoupling near the antenna is not enough,
as the coax will pick up RF again just behind the torroids because of
its close distance to the antenna. Hence the additional coil near the
rear bulkhead.
--
Frans Veldman
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