ordekalo Posted July 23 Report Posted July 23 Hi everyone, I’m in the process of supporting a KNS 80 NAV System installation and wanted to consult the collective wisdom of the Mooney community regarding best practices for shielding and grounding the P801 wiring, specifically for the various NAV/DEV/FLAG lines. I've reviewed the original manuals and wiring diagrams, but a number of points remain ambiguous. I’m hoping some of you have practical experience or updated recommendations for compliance with modern EMI/RFI requirements. Specific questions: NAV FLAG + (Pin 1) & +LEFT DEV (Pin 5): Is there a best-practice for shielding these specific lines? Should the shields be grounded at the equipment, the indicator, or both? Should these lines be routed as shielded twisted pairs or is there a preferred configuration? Other NAV/DEV/FLAG/GS lines on P801: Is individual shielding for each signal line preferred, or can a multi-core shielded cable be used? For those who have done modern avionics retrofits, what routing and shield termination has proven most effective for noise immunity? General KNS 80 integration tips: Any lessons learned, “gotchas”, or recommendations for integrating the KNS 80 into a legacy or glass panel? Are there known issues with certain CDI/HSI models and signal wiring? I’ve attached an extract of the P801 pinout for reference (see below/attached). Your real-world experience and advice would be invaluable and much appreciated!
EricJ Posted July 23 Report Posted July 23 Generally in aviation applications the shield gets grounded on both ends. Do whatever the installation diagrams show, though. Solder sleeves with pigtails, and you can buy them pre-built-in, are often used to provide a fly-wire to ground the shield. It's an easy way to do it and as far as I've seen that's how most people do it these days.
skykrawler Posted July 24 Report Posted July 24 Looking at a diagram, flag connections on a KX155 are not shielded. The deviation signals are a lower level voltage than the flags. Flags are basically discretes (lo/hi) that operate a solenoid.
Mark89114 Posted July 24 Report Posted July 24 16 hours ago, MikeOH said: KNS80??? Someone is missing their doorstop Or boat anchors. I remember using one 40 years ago and thought it was the cats meow....beat using paper and plotter. 1
Slick Nick Posted July 24 Report Posted July 24 Don’t knock it, old stuff can be a great way to upgrade your planes capability for very low cost. With the prevalence of moving map iPads for situational awareness, you don’t need a panel-mounted unit that has a fancy display anymore. I’m still getting around fine IFR on my KLN-89B! Honeywell provides database updates.
MikeOH Posted July 24 Report Posted July 24 5 hours ago, Slick Nick said: Don’t knock it, old stuff can be a great way to upgrade your planes capability for very low cost. With the prevalence of moving map iPads for situational awareness, you don’t need a panel-mounted unit that has a fancy display anymore. I’m still getting around fine IFR on my KLN-89B! Honeywell provides database updates. Fair comment about 'old stuff'. But the KNS-80 (VOR based) is a whole 'nother animal than a KLN-89B (GPS based)! The FAA is shutting down many (most?) VORs. Even the MON (Minimum Operational Network) is a bit of a joke; the POM VOR has been OTS for over a year! And, it is supposed to be part of the MON!! Does it really make sense to spend any money and effort to set up a KNS-80 without much of a VOR network? 1
GeeBee Posted July 25 Report Posted July 25 At the price Garmin 430W and 530W can be had, even with the factory no longer supporting them, they are waaaay better. 1
TaildraggerPilot Posted July 25 Report Posted July 25 10 hours ago, GeeBee said: At the price Garmin 430W and 530W can be had, even with the factory no longer supporting them, they are waaaay better. The GNS-530(W) will be supported for a good while. There’s more money in them for Garmin most likely. 1
TaildraggerPilot Posted July 25 Report Posted July 25 On 7/23/2025 at 5:10 PM, EricJ said: Generally in aviation applications the shield gets grounded on both ends. Do whatever the installation diagrams show, though. Solder sleeves with pigtails, and you can buy them pre-built-in, are often used to provide a fly-wire to ground the shield. It's an easy way to do it and as far as I've seen that's how most people do it these days. There is a huge caveat to that grounding “rule”: audio panel harness shielding.
N201MKTurbo Posted July 25 Report Posted July 25 Your flag and left right signals are low impedance, low power, slow outputs. Shielding is not very important. Shielding is more important on high impedance inputs and high power outputs. These signals are neither. Just a bundle of unshielded wires would work fine if they are going to an indicator where they are driving analog meter movements. If you are running them to some input on some box that will process them for display, it would be good to shield them, because they are going to high impedance inputs. 1
Pinecone Posted July 25 Report Posted July 25 1 hour ago, TaildraggerPilot said: The GNS-530(W) will be supported for a good while. There’s more money in them for Garmin most likely. No, they just still have displays for them. The displays are no longer made and there is not enough demand to start making a batch of 25 year old tech displays.
Slick Nick Posted July 25 Report Posted July 25 19 hours ago, MikeOH said: Fair comment about 'old stuff'. But the KNS-80 (VOR based) is a whole 'nother animal than a KLN-89B (GPS based)! The FAA is shutting down many (most?) VORs. Even the MON (Minimum Operational Network) is a bit of a joke; the POM VOR has been OTS for over a year! And, it is supposed to be part of the MON!! Does it really make sense to spend any money and effort to set up a KNS-80 without much of a VOR network? Oh I thought it was a GPS. My mistake!
Recommended Posts