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toaster73(at)embarqmail.c
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 Posted: Fri Nov 30, 2012 6:39 am Post subject: RF interference on GRT fuel pressure with PTT |
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As you may have seen I posted a problem related to RF interference on my fuel pressure reading provided by GRT EIS 6000 in an RV-10. The pressure would rise to about 45 psi from zero when PTT on the SL30 radio.
Below is what I did thus far.
First thing I did was play with the coax routing from the SL30 to its antenna which is a Bob Archer in the left wingtip. I moved the routing around inside the cabin only. I wonder if this means something about my coax connections or antenna, …anyway I was initially getting about 45 psi rise max from zero with the PTT held in. After moving the coax wire around I get about 23 psi rise.
The coax originally ran from the SL-30 pigtail at panel center along the back of the RV-10 sub panel but kind of out in space then turned to go down the side of the fuselage and then out into the wing. It passed behind the EIS box by about a 10 inches along that sub panel route. As it turned to go down the left fuselage wall it passed by fuel pressure wires coming through the firewall.
The re-route just has it going along the firewall (interior) instead of the subpanel which moves it further from the EIS. It shares some ground wire bundles and is not out in space.
The next thing I did was put the larger (coax size) radio shack ferrite choke around the wires coming out of the sender with a loop around the choke so the wires go through twice. I had bought two smaller chokes (they come 2 to a pack) and I put them just outside the d-sub going into the back of the EIS. I looped the 12 volt regulated supply through one and the signal wire was looped through the second choke. With all that I am down to about 5 psi rise from zero. The funny thing is I had also noticed a movement of -1 or -2 amps with PTT also but didn’t really care about that. But with the 2 smaller chokes around the 12V power and the signal now my amps and fuel pressure move -5 amps and fuel pressure to +5 and they track together. So probably have some trials to do with those chokes such as one or the other or whatever, maybe a third loop. And also check the coax run to the antenna and SWR when I can.
Since I need to get the plane up in the next several days I am calling it good for now. Of course all this could change when I crank up and go fly, but I think I made some headway. At least the high fuel pressure warning probably will not light up now.
-Chris Lucas
N919AR
RV-10 in first conditional inspection
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tim2542(at)sbcglobal.net
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| Posted: Fri Nov 30, 2012 8:26 am Post subject: RF interference on GRT fuel pressure with PTT |
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If it makes you feel better I have the same problem. On mine it only occurs when on the upper end of the band, like center frequencies above 130 MHz, and happens when I key either the 430W or Icom A210 on those upper frequencies.
I spoke to Carlos at GRT about this and he suggested the split ferrite that you have tried. I have not attempted to fix it yet and was about to ask the group what specs I need when I buy it.
I wonder if a small capacitor could be used to drain off the RF since the torrid didn't work. It could be installed inside the D-sub between the fuel sensor pin and ground. Can anyone here tell if this might work and if so what cap to use?
Thanks,
Tim
Sent from my iPad
On Nov 30, 2012, at 6:39 AM, Chris <toaster73(at)embarqmail.com> wrote:
| Quote: |
As you may have seen I posted a problem related to RF interference on my fuel pressure reading provided by GRT EIS 6000 in an RV-10. The pressure would rise to about 45 psi from zero when PTT on the SL30 radio.
Below is what I did thus far.
First thing I did was play with the coax routing from the SL30 to its antenna which is a Bob Archer in the left wingtip. I moved the routing around inside the cabin only. I wonder if this means something about my coax connections or antenna, …anyway I was initially getting about 45 psi rise max from zero with the PTT held in. After moving the coax wire around I get about 23 psi rise.
The coax originally ran from the SL-30 pigtail at panel center along the back of the RV-10 sub panel but kind of out in space then turned to go down the side of the fuselage and then out into the wing. It passed behind the EIS box by about a 10 inches along that sub panel route. As it turned to go down the left fuselage wall it passed by fuel pressure wires coming through the firewall.
The re-route just has it going along the firewall (interior) instead of the subpanel which moves it further from the EIS. It shares some ground wire bundles and is not out in space.
The next thing I did was put the larger (coax size) radio shack ferrite choke around the wires coming out of the sender with a loop around the choke so the wires go through twice. I had bought two smaller chokes (they come 2 to a pack) and I put them just outside the d-sub going into the back of the EIS. I looped the 12 volt regulated supply through one and the signal wire was looped through the second choke. With all that I am down to about 5 psi rise from zero. The funny thing is I had also noticed a movement of -1 or -2 amps with PTT also but didn’t really care about that. But with the 2 smaller chokes around the 12V power and the signal now my amps and fuel pressure move -5 amps and fuel pressure to +5 and they track together. So probably have some trials to do with those chokes such as one or the other or whatever, maybe a third loop. And also check the coax run to the antenna and SWR when I can.
Since I need to get the plane up in the next several days I am calling it good for now. Of course all this could change when I crank up and go fly, but I think I made some headway. At least the high fuel pressure warning probably will not light up now.
-Chris Lucas
N919AR
RV-10 in first conditional inspection
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