I fried a $400 GPS antenna by plugging it in wrong

Working on a King Air at our hangar in Wichita last month, I swapped a GPS antenna without double checking the cable impedance and smoked the receiver on power up. Turned out the old antenna used 50 ohm cable and the replacement was 75 ohm, which I didn't catch until after the magic smoke came out. Anyone else ever mix up coax types and blow something expensive?

2 comments

2 Comments

carter.gavin1mo ago

Man you fried a $400 antenna just from a cable mismatch? That hurts to even read. I always thought impedance was more of a radio frequency thing that only mattered if you were running long cable runs or high power. Never crossed my mind that plugging in the wrong coax on a GPS antenna could actually kill it like that. Guess I've been lucky slapping mismatched cables on stuff without thinking about it too hard.

veraj531mo ago

Oh geez yeah its not just a long cable thing at all. The active GPS antennas have a built in LNA that needs DC bias voltage sent up the coax and if you plug in a cable that shorts that voltage or drops it too much it can pop the little chip right then and there. A lot of those antennas pull like 5 volts through the center conductor and if your cable has a different impedance the voltage drop can get weird and fry the regulator. Ive seen guys kill LNBs on satellite dishes the same way just swapping cables around without checking. Its one of those lessons you only learn once the hard way.