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EFIS breaks Comm squelch

PostPosted: Wed May 21, 2014 12:18 am
by JimB
I have dual Sport HS EFIS. Have been installed for several years. Have always had a problem that the comm squelch on my GNS430 breaks for no reason. Have adjusted the sensitivity of the comm squelch to no avail. Today I experimented and found if I have the 430 powered up and then turn on the EFIS, the squelch breaks. Also if I have the EFIS powered up and the comm squelch breaks, powering off the EFIS restores the squelch. So apparently the EFIS is causing the squelch to break.

I have dual HS Sports, one a S100 MFD and the other a S200 PFD. The S100 MFD is mounted directly above the GNS430. The S200 PFD is above and to the left of the GNS430. I have an ARINC module which is wired to the GNS430 with shielded wire (I think the RS232 from the ARINC to the S200 is unshielded). The magnetometer is wired to the S200 with shielded wire. The GPS serial output from the 430 is wired to the EFIS with shielded wire. The only unshielded connections are the interdisplay RS232, EIS RS232, encoding alt RS232 and RS232 to ARINC. XM weather is wired to the S100 with shielded wire.

The installation is in a Europa which is a composite airframe and instrument panel. I have a ground wire from the S200 chassis to my common ground point. I don't have a similar ground on the S100, but depend on the interconnect wiring for that.

Looking for suggestions to solve the squelch breaking problem. Maybe shielded wires for interdisplay link, EIS input, encoding output and connection to ARINC module?

Jim Butcher
Europa XS

Re: EFIS breaks Comm squelch

PostPosted: Wed May 21, 2014 12:33 am
by Bobturner
I would start by giving the S100 its own ground wire.

Re: EFIS breaks Comm squelch

PostPosted: Thu Jun 26, 2014 8:06 pm
by JimB
Have finally found the problem. I have XM weather which uses a WxWorx reveiver and remote GRT processor. Turns out the WxWorx receiver is creating the noise. It is on its way to them for installation of shielding. I found that booting the EFIS with the power to the WxWorx removed there was no noise. Then insert the power cable to the WxWorx and noise occurred. Very repeatable. Many thanks to Carlos who remembered this being a past problem.

Jim Butcher