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chinesespaceman
Joined: 18 May 2011
Posts: 3
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 Posted: Thu May 26, 2011 10:29 am Post subject: More Strobe Noise |
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Guys, I've been trying for months to get rid of strobe noise, having searched on this site for guidance. If I describe symptoms and cures tried maybe someone can offer a thought?
System is a 2 head Skyflash, with strobes mounted top and bottom of fuselage. Top strobe head is only 18 inches in front of the radio antenna.
I get a crack 2 cracks through the headset each time either of the heads fires. Wiring to the strobe heads is now shielded with the shields from each wire joined and run back to a clean earth.
The noise is not coming through the intercom, only the radio and not on all channels - just the ones I commonly use.......
If I hold a handheld close to the aircraft I can just about hear the strobes firing. Was unable to check the handheld when using my aircraft antenna as different connections.
If I unplug my antenna connection from the rear of the radio I get silence, so deducted that I had RFI that was coming into the radio from either the coax or the core. I ran a temporary wire from my antenna groundplane to a clean earth. Doing this, I got the first 3 cracks, then the noise reduced to a hardly detectable level. Job done, I thought. SO I made this wiring permanent and tested again, same result; job done I thought, so closed everything up.
Flight tested and found it back to it's normal levels - to the point where I won't turn the strobes on unless visibility really requires it.
Is there a filter available to go in line with my coax and the radio?
Should I change the coax to a known high grade and re-route?
Any suggestions welcomed as this is driving me mad.
P.S. I have fitted a forest of earth to this wooden aircraft and run every ground down to this, then it connects through the firewall with a brass bolt to a good earth point on the engine. Aircraft is negative earth.
Thanks in advance
Gavin
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nuckolls.bob(at)aeroelect
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| Posted: Fri May 27, 2011 10:55 am Post subject: More Strobe Noise |
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| Quote: | If I unplug my antenna connection from the rear of the radio I get
silence, so deducted that I had RFI that was coming into the radio
from either the coax or the core. I ran a temporary wire from my
antenna groundplane to a clean earth. Doing this, I got the first 3
cracks, then the noise reduced to a hardly detectable level. Job
done, I thought. SO I made this wiring permanent and tested again,
same result; job done I thought, so closed everything up.
Flight tested and found it back to it's normal levels - to the point
where I won't turn the strobes on unless visibility really requires it.
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Yup. Been there, done that.
When Cessna started looking at white, tip and tail strobes
for the single engine line, we discovered that the flash
tubes themselves are strong radiators of electromagnetic
chaos every time they fire.
I was only peripherally aware of the studies going on
in another area of engineering so I don't know what the
final outcome was. I do recall seeing some strobe tube
heads surrounded by a a fine screen of material grounded
to the head-shell . . . no doubt an experiment to see
if sufficient attenuation of the noise can be achieved.
Eventually, the tip and tail tubes did make it to our
products as a option to replace the legacy rotating beacon.
I don't know what change to design made them acceptable.
This was before DO-160 was being generally applied to all
electro-whizzies on the airplane. All radios were getting
the once-over but it was pretty much up to the installers
at the factory to be system integrators for fans, motors,
and . . . strobes.
| Quote: | Is there a filter available to go in line with my coax and the radio?
Should I change the coax to a known high grade and re-route?
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No, no and no. I suspect that if you conduct yet
another experiment and signal-up your radio from a
an antenna on a long coax and located further from
the airplane, you'll find that the noise goes away.
There's a square-law in general effect here that
says every doubling the distance between victim and antagonist
reduces effects to 1/4.
This is an instance where the 'shielding/filtering' effort
needs to take place at the source. Grounded fine wire mesh
dome or cylinder over the tubes? I wish I could be more
encouraging. Perhaps someone associated more closely
with the early Wheelan/Garmin crowd will recall what
ultimately made these products airplane friendly.
I was outside that loop looking in.
Bob . . .
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