PPt pushed gauges peg (ground)

Gentleman,
When I have the motor running and electricity running through the gauges. When I push the PTT button on both pilots the amp, the EGG and HTG needle peg. Know that it is grounding the gauge needle, when I release PTT the gauges will return to the right position, the gauges are hooked up properly per van instructions, and the PPT is wired properly . All wiring to my Dynon , Icom radio and intercom was pre-wired by APPROACH. everything works except this proplem

If you have a solution, please drop me a line

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Bev Long

A lot more information is needed. Is it an EMS or separate gauges? What equipment manufacturer? DYNON, GARMIN, MGL, JPI, etc?

Step 1: Repeat the test with the com radio turned off. Then you will know if it?s a wiring issue, or an RF getting where it doesn?t belong issue.

BobTurner said:

Step 1: Repeat the test with the com radio turned off. Then you will know if it?s a wiring issue, or an RF getting where it doesn?t belong issue.

Click to expand...

What Bob said.

If problem disappears, look at antenna feedline/connnections/grounding.

If problem remains, look at ground paths.

THE GAUGES ARE SEPARATE. thE RADIO IS A icOM 200. THE INTERCOM IS A ICOM. THE wiring harness was put together by APPROACH. what else do you need to know?

bubba

Bubba

thank you for all your help. Any other Ideas?

bubba

You're getting transmit energy from the VHF coupling into the wiring for your engine gauges. Ammeter and EGT/CHT are very small signals - in the millivolt range; the leakage from the coax is simply coupling far more energy into those wires than the amount of signal that would be generated to drive full scale deflection on the gauge. This is why the gauges peg when you key up the VHF. This is a common scenario in amateur-built aircraft, but it has a very simple and effective solution.

Your VHF comm coax is too close to those small signal wires or to the gauges themselves. Pull the coax out of its current bundle/routing and re-route as far away as possible from those sensitive gauges/wires.

Energy from wires can couple into other wires through the magic of electromagnetism, especially if they are running alongside / parallel to each other. Less chance for coupling exists when the wires cross perpendicularly. Keep this in mind, especially when routing coax. Also, if the coax is the old black-sheathed RG-58, give consideration to replacing it with the new beige/gold coloured RG400. The RG400 stuff has better shielding, so less of the VHF transmit energy escapes through the braid of the coax.

In our aircraft I made three separate bundles running in three separate paths in the aircraft. Audio and other low power / sensitive wiring down the left side, high power circuits down the right side, coax down the middle. Following a technique like this will minimize the likelihood of interference between systems. Keep the coax cables from transmitters (VHF comm, transponder, DME) away from small signal wires and your world will be a happier place.