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-   -   PTT causes EGT displays to change ... ??? (http://www.vansairforce.com/community/showthread.php?t=153252)

Rupester 09-11-2017 05:55 PM

PTT causes EGT displays to change ... ???
 
The other day I noticed for the first time that when transmitted on the comm frequency, the EGTs all changed. Huh? When I let up on the PTT button, all the EGTs returned to their former temps. I don't know if this has been happening for awhile and I just never noticed before ( I'm nearly always looking outside when I talk to ATC, not at the engine data.), or if this is a new phenomenon.
When running LOP with EGTs in the -40 range, they all go to around -50 if the PTT button is depressed briefly. They go to around -60 and seem to top out there when I hold the PTT down longer.
Upon landing, when my EGTs were all showing about 400 degrees on the rich side, the numbers also get bigger on PTT and still about the same 10 to 20 degrees.
CHTs do not change, nor does any other engine data that I can see.

A search of these Forums didn't produce anything. Anybody got an idea of why this might occur?

Bevan 09-11-2017 07:18 PM

It's probably always been happening but you've not noticed it yet. Your eyes have been outside and that's a good thing.

My fuel pressure fluctuates too when I push PTT. It likely has to do with RF getting into the sender or associated wires bringing that signal into the engine monitor or whatever you're using to display the info.

I never noticed it until one day I moved a comm antenna which included extending the feed line. Then the fuel pressure value increased (on PTT) to the point where it tripped my high fuel pressure alarm. That has since been deleted. I suspect the addition of the connectors to lengthen the feed line has caused some leakage or reflection back to the radio causing more RF to be present in the cockpit.

Bevan.

Bevan 09-11-2017 07:22 PM

It's probably always been happening but you've not noticed it yet. Your eyes have been outside and that's a good thing.

My fuel pressure fluctuates when I push PTT. It likely has to do with RF getting into the sender or associated wires bringing that signal into the engine monitor or whatever you're using to display the info.

I never noticed it until one day I moved a comm antenna which included extending the feed line. Then the fuel pressure value increased (on PTT) to the point where it tripped my high fuel pressure alarm. That has since been deleted. I suspect the addition of the connectors to lengthen the feed line has caused some leakage or reflection back to the radio causing more RF to be present in the cockpit.

Bevan.

Rupester 09-11-2017 07:40 PM

Thanks for the info Bevan .... very interesting. I too have GRT gear - 4000 Engine Monitor and dual Sport displays. For comm I use an SL-30. What you say makes sense (.... well, as much sense as you can make with electrical stuff to a mechanical engineer. ;)
The puzzling part is why the CHTs also wouldn't reflect that interference.... those leads run in a bundle with the EGTs. Hmmmmmm.

Mich48041 09-11-2017 07:46 PM

Check all ground wires, especially going to the engine. The engine mount should NOT be used as part of the grounding circuit.

Aluminum 09-11-2017 07:51 PM

Quote:

Originally Posted by Rupester (Post 1203329)
when transmitted on the comm frequency, the EGTs all changed. Huh?

My Dynon SkyView EMS does this too. I have a FL760 mounted inches away from the EMS module. All the RF wiring is very well shielded so I suspect something to do with grounding, or leakage from the radio body itself. I don't worry about it.

airguy 09-11-2017 08:10 PM

Dynon EMS did this on the early units - they came up with a filter to solve the problem but the EMS box had to go back to them to install it, no charge. It's RF power getting into the EGT/CHT sensor loop.

tim2542 09-11-2017 08:12 PM

These little guys fixed the same problem for me:
https://tinyurl.com/y9cpowho
Both my comms on certain channels caused fuel pressure and egt to move. I'm confident it's RF getting into the senders or wires. Anyway, the chokes fixed it nicely. One small one over the fuel pressure wires, and one large one over the entire CHT/EGT harness just before the D-sub connector.
GRT 4000 EIS.
Tim Andres

esco 09-11-2017 08:53 PM

"Oh... that happens to all of them"
 
What I was told when I reported the issue to an "expert"

This with an all steam-gauge panel, years ago...

bruceh 09-11-2017 09:10 PM

Quote:

Originally Posted by airguy (Post 1203382)
Dynon EMS did this on the early units - they came up with a filter to solve the problem but the EMS box had to go back to them to install it, no charge. It's RF power getting into the EGT/CHT sensor loop.

I had this issue also with the Dynon Skyview EMS. Sent it back and they added the filtering and it has been fixed for good. No rewiring needed.


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