nuckolls.bob(at)aeroelect
Guest
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 Posted: Sat Oct 22, 2022 10:29 am Post subject: ****SPAM**** Analogue Engine instruments near VHF radio. |
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At 07:38 AM 10/22/2022, you wrote:
| Quote: | It depends…
Becker comms do not consume much current when not transmitting so are unlikely to cause a problem until the PTT is pressed, if at all. |
90% of time, Comm Tx interference to panel
accessories is due to deficiency in accessory
design . . . not the fault of the transceiver.
I've tested a number of steam guages that
were affected by expected RF energy
sources. Some were affected by extra
strong signals like hand held transceivers
and bubble canopy a/c with an antenna laid
up inside the canopy behind the pilot's
head.
I've seen a couple of instances where a comm
system with satisfactory service history suddenly
becomes a strong antagonist to panel accessories.
Both cases involved the shield connection to
coax connector at the back of the radio becoming
disconnected. This turns the coax feedline
into an antenna that illuminates wiring behind
the panel with strong RF.
| Quote: | The Van’s manifold pressure gauge I had was very susceptible to EMI and would read zero when the PTT was pressed, even with the antenna in the back of the aeroplane.
Some of the other gauges were less sensitive but I suspected the were not well shielded. |
Agreed.
| Quote: | The only real way to find out is suck it and see.
A good grounding scheme will always help along. |
System ground have virtually no influence
on RF interference issues.
| Quote: | | Some manufacturers recommend twisting the power wires, but I’m not convinced that helps and it always assumes the power and ground points are close together which is often not the case. |
A mythical practice not supported in demonstrable
physics.
| Quote: | | Is there any issue placing conventional electric VDO guages very close to the " round hole" Becker comm? |
Vulnerability of the panel accessory can be roughly
evaluated on the bench. Hook it to a power supply
and use a hand-held vhf ratio to check for effects.
If there are no observable effects with the handheld
a foot or so away, the instrument is probably well
designed for such issues. I've seem some Van's
gages go crazy with the radio 2 feet away.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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