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Speedy11(at)aol.com
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 Posted: Sun Oct 25, 2009 10:08 pm Post subject: Confusing |
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Hey guys -
I have a puzzling question for you. At least it's puzzling to me.
I'm studying my downloaded engine monitor data and it appears that when I transmit on the radio that I get an amperage spike and a simultaneous voltage drop. That makes sense - but, at the same time my OAT readings drop several degrees F and then recover to normal after the transmission.
The OAT probe is in a NACA duct on the bottom of the wing and it is exposed to the bent wire radio antenna.
Is it possible that the signal from the radio antenna is affecting the OAT readings when the radio signal hits the OAT probe?
Confused in Daytona Beach,
Stan Sutterfield
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Mon Oct 26, 2009 12:39 pm Post subject: Confusing |
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At 01:04 AM 10/26/2009, you wrote:
| Quote: | Hey guys -
I have a puzzling question for you. At least it's puzzling to me.
I'm studying my downloaded engine monitor data and it appears that when I transmit on the radio that I get an amperage spike and a simultaneous voltage drop. That makes sense - but, at the same time my OAT readings drop several degrees F and then recover to normal after the transmission.
The OAT probe is in a NACA duct on the bottom of the wing and it is exposed to the bent wire radio antenna.
Is it possible that the signal from the radio antenna is affecting the OAT readings when the radio signal hits the OAT probe? |
Sounds like a susceptibility problem with
the instrumentation system. The offending
stimulus (comm transmitter) gets into the
instrumentation electronics via ship's wiring.
Systems destined for installation in TC aircraft
are tested for this effect and filters sufficient
to the task are included inside the instrument
enclosure.
Try putting a dummy load on your antenna coax
AT THE ANTENNA. See:
http://aeroelectric.com/Pictures/Tools/RF_Antenna_Test_Tools/DummyLoad.jpg
if the problem goes away with the dummy load
attached, then you need to add filtering to
the instrumentation system or see if moving the
antenna further way does the job. If the problem
does NOT go away, then you've got a shield ground
open in the feedline between radio and antenna.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
[quote][b]
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